Android源码解析之（九）-->SystemServer进程启动流程

转载请标明出处：一片枫叶的专栏

上面一文中我们讲过Android系统中比较重要的几个进程：init进程，Zygote进程，SystemServer进程已经各种应用进程，其中Zygote进程是整个android系统的根进程，包含SystemServer进程已经各种应用进程在内的进程都是通过Zygote进程fork出来的，具体可参见： android源码解析之（八）–>Zygote进程启动流程

整个系统的android framework进程启动流程如下：

• init进程 –> Zygote进程 –> SystemServer进程 –>各种应用进程

那么SystemServer进程是做什么用的呢？

其实SystemServer进程主要的作用是启动各种系统服务，比如ActivityManagerService，PackageManagerService，WindowManagerService等服务，我们平时熟知的各种系统性的服务其实都是在SystemServer进程中启动的，而当我们的应用需要使用各种系统服务的时候其实也是通过与SystemServer进程通讯获取各种服务对象的句柄的进而执行相应的操作的。

由上一篇文章我们知道SystemServer进程其实也是由Zygote进程fork出来的，并且执行其main方法，那么这里我们以android23的源码为例，看一下SystemServer的main方法的执行逻辑：

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">main</span>(String[] args) {
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> SystemServer().run();
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

这里比较简单，只是new出一个SystemServer对象并执行其run方法，查看SystemServer类的定义我们知道其实final类型的，所以我们不能重写或者继承SystemServer。

然后我们查看SystemServer.run方法的实现：

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() {
        ...
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (System.currentTimeMillis() < EARLIEST_SUPPORTED_TIME) {
            Slog.w(TAG, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"System clock is before 1970; setting to 1970."</span>);
            SystemClock.setCurrentTimeMillis(EARLIEST_SUPPORTED_TIME);
        }

        ...
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!SystemProperties.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">get</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"persist.sys.language"</span>).isEmpty()) {
            final String languageTag = Locale.getDefault().toLanguageTag();

            SystemProperties.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">set</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"persist.sys.locale"</span>, languageTag);
            SystemProperties.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">set</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"persist.sys.language"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">""</span>);
            SystemProperties.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">set</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"persist.sys.country"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">""</span>);
            SystemProperties.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">set</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"persist.sys.localevar"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">""</span>);
        }

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Here we go!</span>
        Slog.i(TAG, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Entered the Android system server!"</span>);
        EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_SYSTEM_RUN, SystemClock.uptimeMillis());

        ...
        SystemProperties.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">set</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"persist.sys.dalvik.vm.lib.2"</span>, VMRuntime.getRuntime().vmLibrary());

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Enable the sampling profiler.</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (SamplingProfilerIntegration.isEnabled()) {
            SamplingProfilerIntegration.start();
            mProfilerSnapshotTimer = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Timer();
            mProfilerSnapshotTimer.schedule(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> TimerTask() {
                @Override
                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() {
                    SamplingProfilerIntegration.writeSnapshot(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"system_server"</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>);
                }
            }, SNAPSHOT_INTERVAL, SNAPSHOT_INTERVAL);
        }

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Mmmmmm... more memory!</span>
        VMRuntime.getRuntime().clearGrowthLimit();

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// The system server has to run all of the time, so it needs to be</span>
        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// as efficient as possible with its memory usage.</span>
        VMRuntime.getRuntime().setTargetHeapUtilization(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0.8</span>f);

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Some devices rely on runtime fingerprint generation, so make sure</span>
        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// we've defined it before booting further.</span>
        Build.ensureFingerprintProperty();

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Within the system server, it is an error to access Environment paths without</span>
        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// explicitly specifying a user.</span>
        Environment.setUserRequired(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>);

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Ensure binder calls into the system always run at foreground priority.</span>
        BinderInternal.disableBackgroundScheduling(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>);

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Prepare the main looper thread (this thread).</span>
        android.os.Process.setThreadPriority(
                android.os.Process.THREAD_PRIORITY_FOREGROUND);
        android.os.Process.setCanSelfBackground(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>);
        Looper.prepareMainLooper();

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Initialize native services.</span>
        System.loadLibrary(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"android_servers"</span>);

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Check whether we failed to shut down last time we tried.</span>
        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// This call may not return.</span>
        performPendingShutdown();

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Initialize the system context.</span>
        createSystemContext();

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Create the system service manager.</span>
        mSystemServiceManager = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> SystemServiceManager(mSystemContext);
        LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Start services.</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
            startBootstrapServices();
            startCoreServices();
            startOtherServices();
        } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (Throwable ex) {
            Slog.e(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"System"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"******************************************"</span>);
            Slog.e(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"System"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"************ Failure starting system services"</span>, ex);
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> ex;
        }

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// For debug builds, log event loop stalls to dropbox for analysis.</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (StrictMode.conditionallyEnableDebugLogging()) {
            Slog.i(TAG, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Enabled StrictMode for system server main thread."</span>);
        }

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Loop forever.</span>
        Looper.loop();
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> RuntimeException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Main thread loop unexpectedly exited"</span>);
    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; 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padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li><li style="box-sizing: border-box; padding: 0px 5px;">82</li><li style="box-sizing: border-box; padding: 0px 5px;">83</li><li style="box-sizing: border-box; padding: 0px 5px;">84</li><li style="box-sizing: border-box; padding: 0px 5px;">85</li><li style="box-sizing: border-box; padding: 0px 5px;">86</li><li style="box-sizing: border-box; padding: 0px 5px;">87</li><li style="box-sizing: border-box; padding: 0px 5px;">88</li><li style="box-sizing: border-box; padding: 0px 5px;">89</li><li style="box-sizing: border-box; padding: 0px 5px;">90</li><li style="box-sizing: border-box; padding: 0px 5px;">91</li><li style="box-sizing: border-box; padding: 0px 5px;">92</li><li style="box-sizing: border-box; padding: 0px 5px;">93</li><li style="box-sizing: border-box; padding: 0px 5px;">94</li></ul>

好吧，代码比较多，慢慢看，先看一下第一段逻辑：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">if (System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.currentTimeMillis</span>() < EARLIEST_SUPPORTED_TIME) {
            Slog<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.w</span>(TAG, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"System clock is before 1970; setting to 1970."</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
            SystemClock<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setCurrentTimeMillis</span>(EARLIEST_SUPPORTED_TIME)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
        }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

首先判断系统当前时间，若当前时间小于1970年1月1日，则一些初始化操作可能会处所，所以当系统的当前时间小于1970年1月1日的时候，设置系统当前时间为该时间点。

然后下面的代码：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">if (!SystemProperties<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.get</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"persist.sys.language"</span>)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.isEmpty</span>()) {
            final String languageTag = Locale<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.getDefault</span>()<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.toLanguageTag</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

            SystemProperties<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.set</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"persist.sys.locale"</span>, languageTag)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
            SystemProperties<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.set</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"persist.sys.language"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">""</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
            SystemProperties<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.set</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"persist.sys.country"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">""</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
            SystemProperties<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.set</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"persist.sys.localevar"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">""</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
        }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>

主要是设置系统的语言环境等； 
下面的主要是设置虚拟机运行内存，加载运行库，设置SystemServer的异步消息，具体的异步消息机制可参见： android源码解析之（二）–>异步消息机制

然后下面的代码首先调用createSystemContext()方法：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">private void createSystemContext() {
        ActivityThread activityThread = ActivityThread<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.systemMain</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
        mSystemContext = activityThread<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.getSystemContext</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
        mSystemContext<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setTheme</span>(android<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.R</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.style</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Theme</span>_DeviceDefault_Light_DarkActionBar)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

可以看到在SystemServer进程中也存在着Context对象，并且是通过ActivityThread.systemMain方法创建context的，这一部分的逻辑以后会通过介绍Activity的启动流程来介绍，这里就不在扩展，这里我们只知道在SystemServer进程中也需要创建Context对象。

然后通过SystemServiceManager的构造方法创建了一个新的SystemServiceManager对象，我们知道SystemServer进程主要是用来构建系统各种service服务的，而SystemServiceManager就是这些服务的管理对象。

然后调用：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">LocalServices<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.addService</span>(SystemServiceManager<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.class</span>, mSystemServiceManager)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

是将SystemServiceManager对象保存SystemServer进程中的一个数据结构中。

最后开始执行：

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Start services.</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
            startBootstrapServices();
            startCoreServices();
            startOtherServices();
        } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (Throwable ex) {
            Slog.e(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"System"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"******************************************"</span>);
            Slog.e(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"System"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"************ Failure starting system services"</span>, ex);
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> ex;
        }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

里面主要涉及了是三个方法： 
startBootstrapServices() 主要用于启动系统Boot级服务 
startCoreServices() 主要用于启动系统核心的服务 
startOtherServices() 主要用于启动一些非紧要或者是非需要及时启动的服务

下面我们重点介绍这三个启动服务的方法，包括启动那些系统服务已经如何启动系统服务等。

首先看一下startBootstrapServices方法：

<code class="hljs lasso has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">void</span> startBootstrapServices() {
        Installer installer <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> mSystemServiceManager<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>startService(Installer<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>class);

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Activity manager runs the show.</span>
        mActivityManagerService <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> mSystemServiceManager<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>startService(
                ActivityManagerService<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>Lifecycle<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>class)<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>getService();
        mActivityManagerService<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>setSystemServiceManager(mSystemServiceManager);
        mActivityManagerService<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>setInstaller(installer);

        mPowerManagerService <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> mSystemServiceManager<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>startService(PowerManagerService<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>class);

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Now that the power manager has been started, let the activity manager</span>
        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// initialize power management features.</span>
        mActivityManagerService<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>initPowerManagement();

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Manages LEDs and display backlight so we need it to bring up the display.</span>
        mSystemServiceManager<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>startService(LightsService<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>class);

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Display manager is needed to provide display metrics before package manager</span>
        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// starts up.</span>
        mDisplayManagerService <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> mSystemServiceManager<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>startService(DisplayManagerService<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>class);

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// We need the default display before we can initialize the package manager.</span>
        mSystemServiceManager<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>startBootPhase(SystemService<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>PHASE_WAIT_FOR_DEFAULT_DISPLAY);

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Only run "core" apps if we're encrypting the device.</span>
        <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">String</span> cryptState <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> SystemProperties<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>get(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"vold.decrypt"</span>);
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (ENCRYPTING_STATE<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">equals</span>(cryptState)) {
            Slog<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>w(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">TAG</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Detected encryption in progress - only parsing core apps"</span>);
            mOnlyCore <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">true</span>;
        } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (ENCRYPTED_STATE<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">equals</span>(cryptState)) {
            Slog<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>w(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">TAG</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Device encrypted - only parsing core apps"</span>);
            mOnlyCore <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">true</span>;
        }

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Start the package manager.</span>
        Slog<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>i(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">TAG</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Package Manager"</span>);
        mPackageManagerService <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> PackageManagerService<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>main(mSystemContext, installer,
                mFactoryTestMode <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">!=</span> FactoryTest<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>FACTORY_TEST_OFF, mOnlyCore);
        mFirstBoot <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> mPackageManagerService<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>isFirstBoot();
        mPackageManager <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> mSystemContext<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>getPackageManager();

        Slog<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>i(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">TAG</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"User Service"</span>);
        ServiceManager<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>addService(Context<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>USER_SERVICE, UserManagerService<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>getInstance());

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Initialize attribute cache used to cache resources from packages.</span>
        AttributeCache<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>init(mSystemContext);

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Set up the Application instance for the system process and get started.</span>
        mActivityManagerService<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>setSystemProcess();

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// The sensor service needs access to package manager service, app ops</span>
        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// service, and permissions service, therefore we start it after them.</span>
        startSensorService();
    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li></ul>

首先执行：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">Installer installer = mSystemServiceManager<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.startService</span>(Installer<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.class</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

mSystemServiceManager是系统服务管理对象，在main方法中已经创建完成，这里我们看一下其startService方法的具体实现：

<code class="hljs actionscript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <T <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> SystemService> T startService(Class<T> serviceClass) {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> String name = serviceClass.getName();
        Slog.i(TAG, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Starting "</span> + name);

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Create the service.</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!SystemService.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span>.isAssignableFrom(serviceClass)) {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> RuntimeException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Failed to create "</span> + name
                    + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">": service must extend "</span> + SystemService.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span>.getName());
        }
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> T service;
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
            Constructor<T> constructor = serviceClass.getConstructor(Context.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span>);
            service = constructor.newInstance(mContext);
        } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (InstantiationException ex) {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> RuntimeException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Failed to create service "</span> + name
                    + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">": service could not be instantiated"</span>, ex);
        } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (IllegalAccessException ex) {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> RuntimeException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Failed to create service "</span> + name
                    + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">": service must have a public constructor with a Context argument"</span>, ex);
        } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (NoSuchMethodException ex) {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> RuntimeException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Failed to create service "</span> + name
                    + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">": service must have a public constructor with a Context argument"</span>, ex);
        } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (InvocationTargetException ex) {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> RuntimeException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Failed to create service "</span> + name
                    + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">": service constructor threw an exception"</span>, ex);
        }

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Register it.</span>
        mServices.add(service);

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Start it.</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
            service.onStart();
        } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (RuntimeException ex) {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> RuntimeException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Failed to start service "</span> + name
                    + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">": onStart threw an exception"</span>, ex);
        }
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> service;
    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li></ul>

可以看到我们通过反射器构造方法创建出服务类，然后添加到SystemServiceManager的服务列表数据中，最后调用了service.onStart()方法，因为我们传递的是Installer.class，我们这里我们查看一下Installer的onStart方法：

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onStart</span>() {
        Slog.i(TAG, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Waiting for installd to be ready."</span>);
        mInstaller.waitForConnection();
    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

很简单就是执行了mInstaller的waitForConnection方法，这里简单介绍一下Installer类，该类是系统安装apk时的一个服务类，继承SystemService（系统服务的一个抽象接口），我们需要在启动完成Installer服务之后才能启动其他的系统服务。 
然后查看waitForConnection（）方法：

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">waitForConnection</span>() {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (;;) {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (execute(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"ping"</span>) >= <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) {
                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span>;
            }
            Slog.w(TAG, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"installd not ready"</span>);
            SystemClock.sleep(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1000</span>);
        }
    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

通过追踪代码可以发现，其在不断的通过ping命令连接Zygote进程（SystemServer和Zygote进程通过socket方式通讯，其他进程通过Binder方式通讯）；

总结： 
在开始执行启动服务之前总是会先尝试通过socket方式连接Zygote进程，在成功连接之后才会开始启动其他服务。

继续来看startBootstrapServices方法：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">// Activity manager runs the show.
        mActivityManagerService = mSystemServiceManager<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.startService</span>(
                ActivityManagerService<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Lifecycle</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.class</span>)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.getService</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
        mActivityManagerService<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setSystemServiceManager</span>(mSystemServiceManager)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
        mActivityManagerService<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setInstaller</span>(installer)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

这段代码主要是用于启动ActivityManagerService服务，并为其设置SysServiceManager和Installer。ActivityManagerService是系统中一个非常重要的服务，Activity，service，Broadcast，contentProvider都需要通过其余系统交互。

首先看一下Lifecycle类的定义：

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Lifecycle</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">SystemService</span> {</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> ActivityManagerService mService;

        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">Lifecycle</span>(Context context) {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>(context);
            mService = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ActivityManagerService(context);
        }

        <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onStart</span>() {
            mService.start();
        }

        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> ActivityManagerService <span class="hljs-title" style="box-sizing: border-box;">getService</span>() {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> mService;
        }
    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul>

可以看到其实ActivityManagerService的一个静态内部类，在其构造方法中会创建一个ActivityManagerService，通过刚刚对Installer服务的分析我们知道，SystemServiceManager的startService方法会调用服务的onStart()方法，而在Lifecycle类的定义中我们看到其onStart（）方法直接调用了mService.start()方法，mService是Lifecycle类中对ActivityManagerService的引用，所以我们可以看一下ActivityManagerService的start方法的实现：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">private void start() {
        Process<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.removeAllProcessGroups</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
        mProcessCpuThread<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.start</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

        mBatteryStatsService<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.publish</span>(mContext)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
        mAppOpsService<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.publish</span>(mContext)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
        Slog<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.d</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"AppOps"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"AppOpsService published"</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
        LocalServices<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.addService</span>(ActivityManagerInternal<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.class</span>, new LocalService())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

由于ActivityManagerService的创建过程比较复杂这里不做过多的分析了，主要是在其构造方法中初始化了一些变量。

然后是启动PowerManagerService服务：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">mPowerManagerService = mSystemServiceManager<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.startService</span>(PowerManagerService<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.class</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

启动方式跟上面的ActivityManagerService服务相似都会调用其构造方法和onStart方法，PowerManagerService主要用于计算系统中和Power相关的计算，然后决策系统应该如何反应。同时协调Power如何与系统其它模块的交互，比如没有用户活动时，屏幕变暗等等。

然后是启动LightsService服务

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">mSystemServiceManager<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.startService</span>(LightsService<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.class</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

主要是手机中关于闪光灯，LED等相关的服务；也是会调用LightsService的构造方法和onStart方法；

然后是启动DisplayManagerService服务

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">mDisplayManagerService = mSystemServiceManager<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.startService</span>(DisplayManagerService<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.class</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

主要是手机显示方面的服务；

然后是启动PackageManagerService，该服务也是android系统中一个比较重要的服务，包括多apk文件的安装，解析，删除，卸载等等操作。

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">Slog<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.i</span>(TAG, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Package Manager"</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
        mPackageManagerService = PackageManagerService<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.main</span>(mSystemContext, installer,
                mFactoryTestMode != FactoryTest<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.FACTORY</span>_TEST_OFF, mOnlyCore)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
        mFirstBoot = mPackageManagerService<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.isFirstBoot</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
        mPackageManager = mSystemContext<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.getPackageManager</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

可以看到PackageManagerService服务的启动方式与其他服务的启动方式有一些区别，直接调用了PackageManagerService的静态main方法，这里我们看一下其main方法的具体实现：

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> PackageManagerService <span class="hljs-title" style="box-sizing: border-box;">main</span>(Context context, Installer installer,
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> factoryTest, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> onlyCore) {
        PackageManagerService m = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> PackageManagerService(context, installer,
                factoryTest, onlyCore);
        ServiceManager.addService(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"package"</span>, m);
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> m;
    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>

可以看到也是直接使用new的方式创建了一个PackageManagerService对象，并在其构造方法中初始化相关变量，最后调用了ServiceManager.addService方法，主要是通过Binder机制与JNI层交互，这里不再扩展。

然后启动UserManagerService和SensorService，至此startBootstrapServices方法执行完成。

然后查看startCoreServices方法：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">private void startCoreServices() {
        // Tracks the battery level.  Requires LightService.
        mSystemServiceManager<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.startService</span>(BatteryService<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.class</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

        // Tracks application usage stats.
        mSystemServiceManager<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.startService</span>(UsageStatsService<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.class</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
        mActivityManagerService<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setUsageStatsManager</span>(
                LocalServices<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.getService</span>(UsageStatsManagerInternal<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.class</span>))<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
        // Update after UsageStatsService is available, needed before performBootDexOpt.
        mPackageManagerService<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.getUsageStatsIfNoPackageUsageInfo</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

        // Tracks whether the updatable WebView is <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> a ready state <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">and</span> watches for update installs.
        mSystemServiceManager<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.startService</span>(WebViewUpdateService<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.class</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li></ul>

可以看到这里启动了BatteryService（电池相关服务），UsageStatsService，WebViewUpdateService服务等。

最后看一下startOtherServices方法，主要用于启动系统中其他的服务，代码很多，这里就不贴代码了，启动的流程和ActivityManagerService的流程类似，会调用服务的构造方法与onStart方法初始化变量。

总结：

• SystemServer进程是android中一个很重要的进程由Zygote进程启动；

• SystemServer进程主要用于启动系统中的服务；

• SystemServer进程启动服务的启动函数为main函数；

• SystemServer在执行过程中首先会初始化一些系统变量，加载类库，创建Context对象，创建SystemServiceManager对象等之后才开始启动系统服务；

• SystemServer进程将系统服务分为三类：boot服务，core服务和other服务，并逐步启动

• SertemServer进程在尝试启动服务之前会首先尝试与Zygote建立socket通讯，只有通讯成功之后才会开始尝试启动服务；

• 创建的系统服务过程中主要通过SystemServiceManager对象来管理，通过调用服务对象的构造方法和onStart方法初始化服务的相关变量；

• 服务对象都有自己的异步消息对象，并运行在单独的线程中；

另外对android源码解析方法感兴趣的可参考我的： 
android源码解析之（一）–>android项目构建过程 
android源码解析之（二）–>异步消息机制 
android源码解析之（三）–>异步任务AsyncTask 
android源码解析之（四）–>HandlerThread 
android源码解析之（五）–>IntentService 
android源码解析之（六）–>Log日志 
android源码解析之（七）–>LruCache 
android源码解析之（八）–>Zygote进程启动流程

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本文以同步至github中：https://github.com/yipianfengye/androidSource，欢迎star和follow