安卓高手之路之ClassLoader(二)

安卓高手之路之ClassLoader(二) - 修补C++ - ITeye技术网站

因为ClassLoader一定与虚拟机的启动有关系，那么必须从Zygote的启动开始看代码。下面就分析一下这些代码，行数不多:

Cpp代码  

1. int main(int argc, const char* const argv[])  
2. {  
3.     // These are global variables in ProcessState.cpp  
4.     //ProcessState.cpp中可能要用到一些main函数。  
5.     mArgC = argc;  
6.     mArgV = argv;  
7.   
8.     mArgLen = 0;  
9.     for (int i=0; i<argc; i++) {  
10.         mArgLen += strlen(argv[i]) + 1;  
11.     }  
12.     mArgLen--;  
13.   
14.     AppRuntime runtime;  
15.     const char* argv0 = argv[0];  
16.   
17.     // Process command line arguments  
18.     // ignore argv[0]  
19.     argc--;  
20.     argv++;  
21.   
22.     // Everything up to '--' or first non '-' arg goes to the vm  
23.   
24.     int i = runtime.addVmArguments(argc, argv);  
25.   
26.     // Parse runtime arguments.  Stop at first unrecognized option.  
27.     bool zygote = false;  
28.     bool startSystemServer = false;  
29.     bool application = false;  
30.     const char* parentDir = NULL;  
31.     const char* niceName = NULL;  
32.     const char* className = NULL;  
33.     while (i < argc) {  
34.         const char* arg = argv[i++];  
35.         if (!parentDir) {  
36.             parentDir = arg;  
37.         } else if (strcmp(arg, "--zygote") == 0) {  
38.             zygote = true;  
39.             niceName = "zygote";  
40.         } else if (strcmp(arg, "--start-system-server") == 0) {  
41.             startSystemServer = true;  
42.         } else if (strcmp(arg, "--application") == 0) {  
43.             application = true;  
44.         } else if (strncmp(arg, "--nice-name=", 12) == 0) {  
45.             niceName = arg + 12;  
46.         } else {  
47.             className = arg;  
48.             break;  
49.         }  
50.     }  
51.   
52.     if (niceName && *niceName) {  
53.         setArgv0(argv0, niceName);  
54.         set_process_name(niceName);  
55.     }  
56.   
57.     runtime.mParentDir = parentDir;  
58.   
59.     if (zygote) {  
60.         runtime.start("com.android.internal.os.ZygoteInit",  
61.                 startSystemServer ? "start-system-server" : "");  
62.     } else if (className) {  
63.         // Remainder of args get passed to startup class main()  
64.         runtime.mClassName = className;  
65.         runtime.mArgC = argc - i;  
66.         runtime.mArgV = argv + i;  
67.         runtime.start("com.android.internal.os.RuntimeInit",  
68.                 application ? "application" : "tool");  
69.     } else {  
70.         fprintf(stderr, "Error: no class name or --zygote supplied.\n");  
71.         app_usage();  
72.         LOG_ALWAYS_FATAL("app_process: no class name or --zygote supplied.");  
73.         return 10;  
74.     }  
75. }  

int main(int argc, const char* const argv[])
{
    // These are global variables in ProcessState.cpp
    //ProcessState.cpp中可能要用到一些main函数。
    mArgC = argc;
    mArgV = argv;

    mArgLen = 0;
    for (int i=0; i<argc; i++) {
        mArgLen += strlen(argv[i]) + 1;
    }
    mArgLen--;

    AppRuntime runtime;
    const char* argv0 = argv[0];

    // Process command line arguments
    // ignore argv[0]
    argc--;
    argv++;

    // Everything up to '--' or first non '-' arg goes to the vm

    int i = runtime.addVmArguments(argc, argv);

    // Parse runtime arguments.  Stop at first unrecognized option.
    bool zygote = false;
    bool startSystemServer = false;
    bool application = false;
    const char* parentDir = NULL;
    const char* niceName = NULL;
    const char* className = NULL;
    while (i < argc) {
        const char* arg = argv[i++];
        if (!parentDir) {
            parentDir = arg;
        } else if (strcmp(arg, "--zygote") == 0) {
            zygote = true;
            niceName = "zygote";
        } else if (strcmp(arg, "--start-system-server") == 0) {
            startSystemServer = true;
        } else if (strcmp(arg, "--application") == 0) {
            application = true;
        } else if (strncmp(arg, "--nice-name=", 12) == 0) {
            niceName = arg + 12;
        } else {
            className = arg;
            break;
        }
    }

    if (niceName && *niceName) {
        setArgv0(argv0, niceName);
        set_process_name(niceName);
    }

    runtime.mParentDir = parentDir;

    if (zygote) {
        runtime.start("com.android.internal.os.ZygoteInit",
                startSystemServer ? "start-system-server" : "");
    } else if (className) {
        // Remainder of args get passed to startup class main()
        runtime.mClassName = className;
        runtime.mArgC = argc - i;
        runtime.mArgV = argv + i;
        runtime.start("com.android.internal.os.RuntimeInit",
                application ? "application" : "tool");
    } else {
        fprintf(stderr, "Error: no class name or --zygote supplied.\n");
        app_usage();
        LOG_ALWAYS_FATAL("app_process: no class name or --zygote supplied.");
        return 10;
    }
}

 分析完之后发现如下参数规律：

 

    1. argv[0]：用这个修改了进程名称。

    2. 虚拟机参数：前面的选项参数都是以“-”打头。被放入了runtime。这些参数被称为是虚拟机参数。

    3.“--”打头的参数是zygote参数。有如下几种，排列顺序如下：

          -runtimearg[0]

         -runtimearg[1]

         。。。。

          parentDir //这个也是runtime使用的，也就是VM使用的。

          className//这个也是runtime使用的，也就是VM使用的。

 

          --zygote

          --start-system-server

          --application

          --nice-name=

 

然后，如果是zygote，那么进入下面这句话

    

C代码  

1. runtime.start("com.android.internal.os.ZygoteInit",  
2.              startSystemServer ? "start-system-server" : "");  

   runtime.start("com.android.internal.os.ZygoteInit",
                startSystemServer ? "start-system-server" : "");

 

 

如果有类名，那么进入下面这句话：

   

C代码  

1. runtime.mClassName = className;  
2.    runtime.mArgC = argc - i; //className，包括className以后的参数个数。  
3.  runtime.mArgV = argv + i; //截止到className的参数个数  
4. runtime.start("com.android.internal.os.RuntimeInit",  
5.               application ? "application" : "tool");  

  runtime.mClassName = className;
     runtime.mArgC = argc - i; //className，包括className以后的参数个数。
   runtime.mArgV = argv + i; //截止到className的参数个数
  runtime.start("com.android.internal.os.RuntimeInit",
                application ? "application" : "tool");

 

 

第一部分：那么开机第一次启动的就一定是，

  

Java代码  

1. runtime.start("com.android.internal.os.ZygoteInit", startSystemServer ? "start-system-server" : "");  

runtime.start("com.android.internal.os.ZygoteInit", startSystemServer ? "start-system-server" : "");

 其中startSystemServer 由init.rc指定，在目录android40\system\core\rootdir中的init.rc.

   service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server
    class main
    socket zygote stream 660 root system
    onrestart write /sys/android_power/request_state wake
    onrestart write /sys/power/state on
    onrestart restart media
    onrestart restart netd

 

第二部分：从ActivityManagerService可以看出，--application并没有指定，这句话也就相当于：

C代码  

1. runtime.start("com.android.internal.os.RuntimeInit", "tool");  

runtime.start("com.android.internal.os.RuntimeInit", "tool");

 现在代码分成了两部分。

 

那么先分析第一部分。

那么zygote启动到底配置了那些参数呢，我们就看一看：

   service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server

根据上面说的参数序列图，可以看出。

   runtime.mParentDir  为/system/bin

   runtime的一个arg为-Xzygote

那么这个这个start函数就变成：

C代码  

1. runtime.start("com.android.internal.os.ZygoteInit",  "start-system-server");  

runtime.start("com.android.internal.os.ZygoteInit",  "start-system-server");

 

 

代码进入到base/core/jni目录的AndroidRuntime.cpp里面。这个函数还不算长，就直接贴出来看一下，注意注释，由此可以看出这个就是启动虚拟机的代码所在啊。那么既然Zygote进程也是这么启动的，那么我们就有理由断定Zygote也是个Dalvik虚拟机！事情是不是这样呢？那么就带着这个疑问去分析一下：

 

Cpp代码  

1. /* 
2.  * Start the Android runtime.  This involves starting the virtual machine 
3.  * and calling the "static void main(String[] args)" method in the class 
4.  * named by "className". 
5.  * 
6.  * Passes the main function two arguments, the class name and the specified 
7.  * options string. 
8.  */  
9. void AndroidRuntime::start(const char* className, const char* options)  
10. {  
11.     LOGD("\n>>>>>> AndroidRuntime START %s <<<<<<\n",  
12.             className != NULL ? className : "(unknown)");  
13.   
14.     blockSigpipe();  
15.   
16.     /* 
17.      * 'startSystemServer == true' means runtime is obsolete and not run from 
18.      * init.rc anymore, so we print out the boot start event here. 
19.      */  
20.     if (strcmp(options, "start-system-server") == 0) {  
21.         /* track our progress through the boot sequence */  
22.         const int LOG_BOOT_PROGRESS_START = 3000;  
23.         LOG_EVENT_LONG(LOG_BOOT_PROGRESS_START,  
24.                        ns2ms(systemTime(SYSTEM_TIME_MONOTONIC)));  
25.     }  
26.   
27.     const char* rootDir = getenv("ANDROID_ROOT");  
28.     if (rootDir == NULL) {  
29.         rootDir = "/system";  
30.         if (!hasDir("/system")) {  
31.             LOG_FATAL("No root directory specified, and /android does not exist.");  
32.             return;  
33.         }  
34.         setenv("ANDROID_ROOT", rootDir, 1);  
35.     }  
36.   
37.     //const char* kernelHack = getenv("LD_ASSUME_KERNEL");  
38.     //LOGD("Found LD_ASSUME_KERNEL='%s'\n", kernelHack);  
39.   
40.     /* start the virtual machine */  
41.     JNIEnv* env;  
42.     if (startVm(&mJavaVM, &env) != 0) {  
43.         return;  
44.     }  
45.     onVmCreated(env);  
46.   
47.     /* 
48.      * Register android functions. 
49.      */  
50.     if (startReg(env) < 0) {  
51.         LOGE("Unable to register all android natives\n");  
52.         return;  
53.     }  
54.   
55.     /* 
56.      * We want to call main() with a String array with arguments in it. 
57.      * At present we have two arguments, the class name and an option string. 
58.      * Create an array to hold them. 
59.      */  
60.     jclass stringClass;  
61.     jobjectArray strArray;  
62.     jstring classNameStr;  
63.     jstring optionsStr;  
64.   
65.     stringClass = env->FindClass("java/lang/String");  
66.     assert(stringClass != NULL);  
67.     strArray = env->NewObjectArray(2, stringClass, NULL);  
68.     assert(strArray != NULL);  
69.     classNameStr = env->NewStringUTF(className);  
70.     assert(classNameStr != NULL);  
71.     env->SetObjectArrayElement(strArray, 0, classNameStr);  
72.     optionsStr = env->NewStringUTF(options);  
73.     env->SetObjectArrayElement(strArray, 1, optionsStr);  
74.   
75.     /* 
76.      * Start VM.  This thread becomes the main thread of the VM, and will 
77.      * not return until the VM exits. 
78.      */  
79.     char* slashClassName = toSlashClassName(className);  
80.     jclass startClass = env->FindClass(slashClassName);  
81.     if (startClass == NULL) {  
82.         LOGE("JavaVM unable to locate class '%s'\n", slashClassName);  
83.         /* keep going */  
84.     } else {  
85.         jmethodID startMeth = env->GetStaticMethodID(startClass, "main",  
86.             "([Ljava/lang/String;)V");  
87.         if (startMeth == NULL) {  
88.             LOGE("JavaVM unable to find main() in '%s'\n", className);  
89.             /* keep going */  
90.         } else {  
91.             env->CallStaticVoidMethod(startClass, startMeth, strArray);  
92.   
93. #if 0  
94.             if (env->ExceptionCheck())  
95.                 threadExitUncaughtException(env);  
96. #endif  
97.         }  
98.     }  
99.     free(slashClassName);  
100.   
101.     LOGD("Shutting down VM\n");  
102.     if (mJavaVM->DetachCurrentThread() != JNI_OK)  
103.         LOGW("Warning: unable to detach main thread\n");  
104.     if (mJavaVM->DestroyJavaVM() != 0)  
105.         LOGW("Warning: VM did not shut down cleanly\n");  
106. }  

/*
 * Start the Android runtime.  This involves starting the virtual machine
 * and calling the "static void main(String[] args)" method in the class
 * named by "className".
 *
 * Passes the main function two arguments, the class name and the specified
 * options string.
 */
void AndroidRuntime::start(const char* className, const char* options)
{
    LOGD("\n>>>>>> AndroidRuntime START %s <<<<<<\n",
            className != NULL ? className : "(unknown)");

    blockSigpipe();

    /*
     * 'startSystemServer == true' means runtime is obsolete and not run from
     * init.rc anymore, so we print out the boot start event here.
     */
    if (strcmp(options, "start-system-server") == 0) {
        /* track our progress through the boot sequence */
        const int LOG_BOOT_PROGRESS_START = 3000;
        LOG_EVENT_LONG(LOG_BOOT_PROGRESS_START,
                       ns2ms(systemTime(SYSTEM_TIME_MONOTONIC)));
    }

    const char* rootDir = getenv("ANDROID_ROOT");
    if (rootDir == NULL) {
        rootDir = "/system";
        if (!hasDir("/system")) {
            LOG_FATAL("No root directory specified, and /android does not exist.");
            return;
        }
        setenv("ANDROID_ROOT", rootDir, 1);
    }

    //const char* kernelHack = getenv("LD_ASSUME_KERNEL");
    //LOGD("Found LD_ASSUME_KERNEL='%s'\n", kernelHack);

    /* start the virtual machine */
    JNIEnv* env;
    if (startVm(&mJavaVM, &env) != 0) {
        return;
    }
    onVmCreated(env);

    /*
     * Register android functions.
     */
    if (startReg(env) < 0) {
        LOGE("Unable to register all android natives\n");
        return;
    }

    /*
     * We want to call main() with a String array with arguments in it.
     * At present we have two arguments, the class name and an option string.
     * Create an array to hold them.
     */
    jclass stringClass;
    jobjectArray strArray;
    jstring classNameStr;
    jstring optionsStr;

    stringClass = env->FindClass("java/lang/String");
    assert(stringClass != NULL);
    strArray = env->NewObjectArray(2, stringClass, NULL);
    assert(strArray != NULL);
    classNameStr = env->NewStringUTF(className);
    assert(classNameStr != NULL);
    env->SetObjectArrayElement(strArray, 0, classNameStr);
    optionsStr = env->NewStringUTF(options);
    env->SetObjectArrayElement(strArray, 1, optionsStr);

    /*
     * Start VM.  This thread becomes the main thread of the VM, and will
     * not return until the VM exits.
     */
    char* slashClassName = toSlashClassName(className);
    jclass startClass = env->FindClass(slashClassName);
    if (startClass == NULL) {
        LOGE("JavaVM unable to locate class '%s'\n", slashClassName);
        /* keep going */
    } else {
        jmethodID startMeth = env->GetStaticMethodID(startClass, "main",
            "([Ljava/lang/String;)V");
        if (startMeth == NULL) {
            LOGE("JavaVM unable to find main() in '%s'\n", className);
            /* keep going */
        } else {
            env->CallStaticVoidMethod(startClass, startMeth, strArray);

#if 0
            if (env->ExceptionCheck())
                threadExitUncaughtException(env);
#endif
        }
    }
    free(slashClassName);

    LOGD("Shutting down VM\n");
    if (mJavaVM->DetachCurrentThread() != JNI_OK)
        LOGW("Warning: unable to detach main thread\n");
    if (mJavaVM->DestroyJavaVM() != 0)
        LOGW("Warning: VM did not shut down cleanly\n");
}

 

linux的POSIX (Portable Operating System Interface of Unix)我不懂。但是从直观上看，可能是一种禁止打断进程的方法：

 

Cpp代码  

1. LOGD("\n>>>>>> AndroidRuntime START %s <<<<<<\n",  
2.         className != NULL ? className : "(unknown)");  
3.   
4. blockSigpipe();  

    LOGD("\n>>>>>> AndroidRuntime START %s <<<<<<\n",
            className != NULL ? className : "(unknown)");

    blockSigpipe();

 下面这句话毫无意义，就是打印log

  

Cpp代码  

1. if (strcmp(options, "start-system-server") == 0) {  
2.         /* track our progress through the boot sequence */  
3.         const int LOG_BOOT_PROGRESS_START = 3000;  
4.         LOG_EVENT_LONG(LOG_BOOT_PROGRESS_START,  
5.                        ns2ms(systemTime(SYSTEM_TIME_MONOTONIC)));  
6.     }  

if (strcmp(options, "start-system-server") == 0) {
        /* track our progress through the boot sequence */
        const int LOG_BOOT_PROGRESS_START = 3000;
        LOG_EVENT_LONG(LOG_BOOT_PROGRESS_START,
                       ns2ms(systemTime(SYSTEM_TIME_MONOTONIC)));
    }

 下面这句话定义androidroot的目录

 

  

Java代码  

1. const char* rootDir = getenv("ANDROID_ROOT");  
2.  if (rootDir == NULL) {  
3.      rootDir = "/system";  
4.      if (!hasDir("/system")) {  
5.          LOG_FATAL("No root directory specified, and /android does not exist.");  
6.          return;  
7.      }  
8.      setenv("ANDROID_ROOT", rootDir, 1);  
9.  }  

   const char* rootDir = getenv("ANDROID_ROOT");
    if (rootDir == NULL) {
        rootDir = "/system";
        if (!hasDir("/system")) {
            LOG_FATAL("No root directory specified, and /android does not exist.");
            return;
        }
        setenv("ANDROID_ROOT", rootDir, 1);
    }

 对照init.rc可以知道，就是/system

 

 

Python代码  

1. # setup the global environment  
2.     export PATH /sbin:/vendor/bin:/system/sbin:/system/bin:/system/xbin  
3.     export LD_LIBRARY_PATH /vendor/lib:/system/lib  
4.     export ANDROID_BOOTLOGO 1  
5.     export ANDROID_ROOT /system  
6.     export ANDROID_ASSETS /system/app  
7.     export ANDROID_DATA /data  
8.     export ASEC_MOUNTPOINT /mnt/asec  
9.     export LOOP_MOUNTPOINT /mnt/obb  
10.     export BOOTCLASSPATH /system/framework/core.jar:/system/framework/core-junit.jar:/system/framework/bouncycastle.jar:/system/framework/ext.jar:/system/framework/framework.jar:/system/framework/android.policy.jar:/system/framework/services.jar:/system/framework/apache-xml.jar:/system/framework/filterfw.jar  

# setup the global environment
    export PATH /sbin:/vendor/bin:/system/sbin:/system/bin:/system/xbin
    export LD_LIBRARY_PATH /vendor/lib:/system/lib
    export ANDROID_BOOTLOGO 1
    export ANDROID_ROOT /system
    export ANDROID_ASSETS /system/app
    export ANDROID_DATA /data
    export ASEC_MOUNTPOINT /mnt/asec
    export LOOP_MOUNTPOINT /mnt/obb
    export BOOTCLASSPATH /system/framework/core.jar:/system/framework/core-junit.jar:/system/framework/bouncycastle.jar:/system/framework/ext.jar:/system/framework/framework.jar:/system/framework/android.policy.jar:/system/framework/services.jar:/system/framework/apache-xml.jar:/system/framework/filterfw.jar

 

主要是下面这两句话

 

Java代码  

1. /* start the virtual machine */  
2.   JNIEnv* env;  
3.   if (startVm(&mJavaVM, &env) != 0) {  
4.       return;  
5.   }  
6.   onVmCreated(env);  
7.   
8.   /* 
9.    * Register android functions. 
10.    */  
11.   if (startReg(env) < 0) {  
12.       LOGE("Unable to register all android natives\n");  
13.       return;  
14.   }  

  /* start the virtual machine */
    JNIEnv* env;
    if (startVm(&mJavaVM, &env) != 0) {
        return;
    }
    onVmCreated(env);

    /*
     * Register android functions.
     */
    if (startReg(env) < 0) {
        LOGE("Unable to register all android natives\n");
        return;
    }

 

 

 一个启动虚拟机，一个启动注册安卓本地方法。虚拟机的启动流程，最终调用的是

JNI_CreateJavaVM 在framework/base/core/jni/AndroidRuntime.cpp下。JNI_CreateJavaVM 调用的是：

 然后调用dalvik/vm/Jni.cpp的JNI_CreateJavaVM 方法：

 

Cpp代码  

1. jint JNI_CreateJavaVM(JavaVM** p_vm, JNIEnv** p_env, void* vm_args) {  
2.     const JavaVMInitArgs* args = (JavaVMInitArgs*) vm_args;  
3.     if (args->version < JNI_VERSION_1_2) {  
4.         return JNI_EVERSION;  
5.     }  
6.   
7.     // TODO: don't allow creation of multiple VMs -- one per customer for now  
8.   
9.     /* zero globals; not strictly necessary the first time a VM is started */  
10.     memset(&gDvm, 0, sizeof(gDvm));  
11.   
12.     /* 
13.      * Set up structures for JNIEnv and VM. 
14.      */  
15.     JavaVMExt* pVM = (JavaVMExt*) malloc(sizeof(JavaVMExt));  
16.     memset(pVM, 0, sizeof(JavaVMExt));  
17.     pVM->funcTable = &gInvokeInterface;  
18.     pVM->envList = NULL;  
19.     dvmInitMutex(&pVM->envListLock);  
20.   
21.     UniquePtr<const char*[]> argv(new const char*[args->nOptions]);  
22.     memset(argv.get(), 0, sizeof(char*) * (args->nOptions));  
23.   
24.     /* 
25.      * Convert JNI args to argv. 
26.      * 
27.      * We have to pull out vfprintf/exit/abort, because they use the 
28.      * "extraInfo" field to pass function pointer "hooks" in.  We also 
29.      * look for the -Xcheck:jni stuff here. 
30.      */  
31.     int argc = 0;  
32.     for (int i = 0; i < args->nOptions; i++) {  
33.         const char* optStr = args->options[i].optionString;  
34.         if (optStr == NULL) {  
35.             dvmFprintf(stderr, "ERROR: CreateJavaVM failed: argument %d was NULL\n", i);  
36.             return JNI_ERR;  
37.         } else if (strcmp(optStr, "vfprintf") == 0) {  
38.             gDvm.vfprintfHook = (int (*)(FILE *, const char*, va_list))args->options[i].extraInfo;  
39.         } else if (strcmp(optStr, "exit") == 0) {  
40.             gDvm.exitHook = (void (*)(int)) args->options[i].extraInfo;  
41.         } else if (strcmp(optStr, "abort") == 0) {  
42.             gDvm.abortHook = (void (*)(void))args->options[i].extraInfo;  
43.         } else if (strcmp(optStr, "sensitiveThread") == 0) {  
44.             gDvm.isSensitiveThreadHook = (bool (*)(void))args->options[i].extraInfo;  
45.         } else if (strcmp(optStr, "-Xcheck:jni") == 0) {  
46.             gDvmJni.useCheckJni = true;  
47.         } else if (strncmp(optStr, "-Xjniopts:", 10) == 0) {  
48.             char* jniOpts = strdup(optStr + 10);  
49.             size_t jniOptCount = 1;  
50.             for (char* p = jniOpts; *p != 0; ++p) {  
51.                 if (*p == ',') {  
52.                     ++jniOptCount;  
53.                     *p = 0;  
54.                 }  
55.             }  
56.             char* jniOpt = jniOpts;  
57.             for (size_t i = 0; i < jniOptCount; ++i) {  
58.                 if (strcmp(jniOpt, "warnonly") == 0) {  
59.                     gDvmJni.warnOnly = true;  
60.                 } else if (strcmp(jniOpt, "forcecopy") == 0) {  
61.                     gDvmJni.forceCopy = true;  
62.                 } else if (strcmp(jniOpt, "logThirdPartyJni") == 0) {  
63.                     gDvmJni.logThirdPartyJni = true;  
64.                 } else {  
65.                     dvmFprintf(stderr, "ERROR: CreateJavaVM failed: unknown -Xjniopts option '%s'\n",  
66.                             jniOpt);  
67.                     return JNI_ERR;  
68.                 }  
69.                 jniOpt += strlen(jniOpt) + 1;  
70.             }  
71.             free(jniOpts);  
72.         } else {  
73.             /* regular option */  
74.             argv[argc++] = optStr;  
75.         }  
76.     }  
77.   
78.     if (gDvmJni.useCheckJni) {  
79.         dvmUseCheckedJniVm(pVM);  
80.     }  
81.   
82.     if (gDvmJni.jniVm != NULL) {  
83.         dvmFprintf(stderr, "ERROR: Dalvik only supports one VM per process\n");  
84.         return JNI_ERR;  
85.     }  
86.     gDvmJni.jniVm = (JavaVM*) pVM;  
87.   
88.     /* 
89.      * Create a JNIEnv for the main thread.  We need to have something set up 
90.      * here because some of the class initialization we do when starting 
91.      * up the VM will call into native code. 
92.      */  
93.     JNIEnvExt* pEnv = (JNIEnvExt*) dvmCreateJNIEnv(NULL);  
94.   
95.     /* Initialize VM. */  
96.     gDvm.initializing = true;  
97.     std::string status =  
98.             dvmStartup(argc, argv.get(), args->ignoreUnrecognized, (JNIEnv*)pEnv);  
99.     gDvm.initializing = false;  
100.   
101.     if (!status.empty()) {  
102.         free(pEnv);  
103.         free(pVM);  
104.         LOGW("CreateJavaVM failed: %s", status.c_str());  
105.         return JNI_ERR;  
106.     }  
107.   
108.     /* 
109.      * Success!  Return stuff to caller. 
110.      */  
111.     dvmChangeStatus(NULL, THREAD_NATIVE);  
112.     *p_env = (JNIEnv*) pEnv;  
113.     *p_vm = (JavaVM*) pVM;  
114.     LOGV("CreateJavaVM succeeded");  
115.     return JNI_OK;  
116. }  

jint JNI_CreateJavaVM(JavaVM** p_vm, JNIEnv** p_env, void* vm_args) {
    const JavaVMInitArgs* args = (JavaVMInitArgs*) vm_args;
    if (args->version < JNI_VERSION_1_2) {
        return JNI_EVERSION;
    }

    // TODO: don't allow creation of multiple VMs -- one per customer for now

    /* zero globals; not strictly necessary the first time a VM is started */
    memset(&gDvm, 0, sizeof(gDvm));

    /*
     * Set up structures for JNIEnv and VM.
     */
    JavaVMExt* pVM = (JavaVMExt*) malloc(sizeof(JavaVMExt));
    memset(pVM, 0, sizeof(JavaVMExt));
    pVM->funcTable = &gInvokeInterface;
    pVM->envList = NULL;
    dvmInitMutex(&pVM->envListLock);

    UniquePtr<const char*[]> argv(new const char*[args->nOptions]);
    memset(argv.get(), 0, sizeof(char*) * (args->nOptions));

    /*
     * Convert JNI args to argv.
     *
     * We have to pull out vfprintf/exit/abort, because they use the
     * "extraInfo" field to pass function pointer "hooks" in.  We also
     * look for the -Xcheck:jni stuff here.
     */
    int argc = 0;
    for (int i = 0; i < args->nOptions; i++) {
        const char* optStr = args->options[i].optionString;
        if (optStr == NULL) {
            dvmFprintf(stderr, "ERROR: CreateJavaVM failed: argument %d was NULL\n", i);
            return JNI_ERR;
        } else if (strcmp(optStr, "vfprintf") == 0) {
            gDvm.vfprintfHook = (int (*)(FILE *, const char*, va_list))args->options[i].extraInfo;
        } else if (strcmp(optStr, "exit") == 0) {
            gDvm.exitHook = (void (*)(int)) args->options[i].extraInfo;
        } else if (strcmp(optStr, "abort") == 0) {
            gDvm.abortHook = (void (*)(void))args->options[i].extraInfo;
        } else if (strcmp(optStr, "sensitiveThread") == 0) {
            gDvm.isSensitiveThreadHook = (bool (*)(void))args->options[i].extraInfo;
        } else if (strcmp(optStr, "-Xcheck:jni") == 0) {
            gDvmJni.useCheckJni = true;
        } else if (strncmp(optStr, "-Xjniopts:", 10) == 0) {
            char* jniOpts = strdup(optStr + 10);
            size_t jniOptCount = 1;
            for (char* p = jniOpts; *p != 0; ++p) {
                if (*p == ',') {
                    ++jniOptCount;
                    *p = 0;
                }
            }
            char* jniOpt = jniOpts;
            for (size_t i = 0; i < jniOptCount; ++i) {
                if (strcmp(jniOpt, "warnonly") == 0) {
                    gDvmJni.warnOnly = true;
                } else if (strcmp(jniOpt, "forcecopy") == 0) {
                    gDvmJni.forceCopy = true;
                } else if (strcmp(jniOpt, "logThirdPartyJni") == 0) {
                    gDvmJni.logThirdPartyJni = true;
                } else {
                    dvmFprintf(stderr, "ERROR: CreateJavaVM failed: unknown -Xjniopts option '%s'\n",
                            jniOpt);
                    return JNI_ERR;
                }
                jniOpt += strlen(jniOpt) + 1;
            }
            free(jniOpts);
        } else {
            /* regular option */
            argv[argc++] = optStr;
        }
    }

    if (gDvmJni.useCheckJni) {
        dvmUseCheckedJniVm(pVM);
    }

    if (gDvmJni.jniVm != NULL) {
        dvmFprintf(stderr, "ERROR: Dalvik only supports one VM per process\n");
        return JNI_ERR;
    }
    gDvmJni.jniVm = (JavaVM*) pVM;

    /*
     * Create a JNIEnv for the main thread.  We need to have something set up
     * here because some of the class initialization we do when starting
     * up the VM will call into native code.
     */
    JNIEnvExt* pEnv = (JNIEnvExt*) dvmCreateJNIEnv(NULL);

    /* Initialize VM. */
    gDvm.initializing = true;
    std::string status =
            dvmStartup(argc, argv.get(), args->ignoreUnrecognized, (JNIEnv*)pEnv);
    gDvm.initializing = false;

    if (!status.empty()) {
        free(pEnv);
        free(pVM);
        LOGW("CreateJavaVM failed: %s", status.c_str());
        return JNI_ERR;
    }

    /*
     * Success!  Return stuff to caller.
     */
    dvmChangeStatus(NULL, THREAD_NATIVE);
    *p_env = (JNIEnv*) pEnv;
    *p_vm = (JavaVM*) pVM;
    LOGV("CreateJavaVM succeeded");
    return JNI_OK;
}

 

 

  然后调用Jni.cpp中的

 

Java代码  

1. /* 
2.  * Create a new JNIEnv struct and add it to the VM's list. 
3.  * 
4.  * "self" will be NULL for the main thread, since the VM hasn't started 
5.  * yet; the value will be filled in later. 
6.  */  
7. JNIEnv* dvmCreateJNIEnv(Thread* self) {  
8.     JavaVMExt* vm = (JavaVMExt*) gDvmJni.jniVm;  
9.   
10.     //if (self != NULL)  
11.     //    LOGI("Ent CreateJNIEnv: threadid=%d %p", self->threadId, self);  
12.   
13.     assert(vm != NULL);  
14.   
15.     JNIEnvExt* newEnv = (JNIEnvExt*) calloc(1, sizeof(JNIEnvExt));  
16.     newEnv->funcTable = &gNativeInterface;  
17.     if (self != NULL) {  
18.         dvmSetJniEnvThreadId((JNIEnv*) newEnv, self);  
19.         assert(newEnv->envThreadId != 0);  
20.     } else {  
21.         /* make it obvious if we fail to initialize these later */  
22.         newEnv->envThreadId = 0x77777775;  
23.         newEnv->self = (Thread*) 0x77777779;  
24.     }  
25.     if (gDvmJni.useCheckJni) {  
26.         dvmUseCheckedJniEnv(newEnv);  
27.     }  
28.   
29.     ScopedPthreadMutexLock lock(&vm->envListLock);  
30.   
31.     /* insert at head of list */  
32.     newEnv->next = vm->envList;  
33.     assert(newEnv->prev == NULL);  
34.     if (vm->envList == NULL) {  
35.         // rare, but possible  
36.         vm->envList = newEnv;  
37.     } else {  
38.         vm->envList->prev = newEnv;  
39.     }  
40.     vm->envList = newEnv;  
41.   
42.     //if (self != NULL)  
43.     //    LOGI("Xit CreateJNIEnv: threadid=%d %p", self->threadId, self);  
44.     return (JNIEnv*) newEnv;  
45. }  

/*
 * Create a new JNIEnv struct and add it to the VM's list.
 *
 * "self" will be NULL for the main thread, since the VM hasn't started
 * yet; the value will be filled in later.
 */
JNIEnv* dvmCreateJNIEnv(Thread* self) {
    JavaVMExt* vm = (JavaVMExt*) gDvmJni.jniVm;

    //if (self != NULL)
    //    LOGI("Ent CreateJNIEnv: threadid=%d %p", self->threadId, self);

    assert(vm != NULL);

    JNIEnvExt* newEnv = (JNIEnvExt*) calloc(1, sizeof(JNIEnvExt));
    newEnv->funcTable = &gNativeInterface;
    if (self != NULL) {
        dvmSetJniEnvThreadId((JNIEnv*) newEnv, self);
        assert(newEnv->envThreadId != 0);
    } else {
        /* make it obvious if we fail to initialize these later */
        newEnv->envThreadId = 0x77777775;
        newEnv->self = (Thread*) 0x77777779;
    }
    if (gDvmJni.useCheckJni) {
        dvmUseCheckedJniEnv(newEnv);
    }

    ScopedPthreadMutexLock lock(&vm->envListLock);

    /* insert at head of list */
    newEnv->next = vm->envList;
    assert(newEnv->prev == NULL);
    if (vm->envList == NULL) {
        // rare, but possible
        vm->envList = newEnv;
    } else {
        vm->envList->prev = newEnv;
    }
    vm->envList = newEnv;

    //if (self != NULL)
    //    LOGI("Xit CreateJNIEnv: threadid=%d %p", self->threadId, self);
    return (JNIEnv*) newEnv;
}

 

 

   好吧，这些全是些乱七八糟的东西。真正启动的是这句话，Jni.cpp中：

  

Java代码  

1. std::string status =  
2.            dvmStartup(argc, argv.get(), args->ignoreUnrecognized, (JNIEnv*)pEnv);  

 std::string status =
            dvmStartup(argc, argv.get(), args->ignoreUnrecognized, (JNIEnv*)pEnv);

 

 

 在Dalvik/vm/Init.cpp中

Cpp代码  

1. *  
2.  * VM initialization.  Pass in any options provided on the command line.  
3.  * Do not pass in the class name or the options for the class.  
4.  *  
5.  * Returns 0 on success.  
6.  */  
7. std::string dvmStartup(int argc, const char* const argv[],  
8.         bool ignoreUnrecognized, JNIEnv* pEnv)  
9. {  
10.     ScopedShutdown scopedShutdown;  
11.   
12.     assert(gDvm.initializing);  
13.   
14.     LOGV("VM init args (%d):", argc);  
15.     for (int i = 0; i < argc; i++) {  
16.         LOGV("  %d: '%s'", i, argv[i]);  
17.     }  
18.     setCommandLineDefaults();  
19.   
20.     /* 
21.      * Process the option flags (if any). 
22.      */  
23.     int cc = processOptions(argc, argv, ignoreUnrecognized);  
24.     if (cc != 0) {  
25.         if (cc < 0) {  
26.             dvmFprintf(stderr, "\n");  
27.             usage("dalvikvm");  
28.         }  
29.         return "syntax error";  
30.     }  
31.   
32. #if WITH_EXTRA_GC_CHECKS > 1  
33.     /* only "portable" interp has the extra goodies */  
34.     if (gDvm.executionMode != kExecutionModeInterpPortable) {  
35.         LOGI("Switching to 'portable' interpreter for GC checks");  
36.         gDvm.executionMode = kExecutionModeInterpPortable;  
37.     }  
38. #endif  
39.   
40.     /* Configure group scheduling capabilities */  
41.     if (!access("/dev/cpuctl/tasks", F_OK)) {  
42.         LOGV("Using kernel group scheduling");  
43.         gDvm.kernelGroupScheduling = 1;  
44.     } else {  
45.         LOGV("Using kernel scheduler policies");  
46.     }  
47.   
48.     /* configure signal handling */  
49.     if (!gDvm.reduceSignals)  
50.         blockSignals();  
51.   
52.     /* verify system page size */  
53.     if (sysconf(_SC_PAGESIZE) != SYSTEM_PAGE_SIZE) {  
54.         return StringPrintf("expected page size %d, got %d",  
55.                 SYSTEM_PAGE_SIZE, (int) sysconf(_SC_PAGESIZE));  
56.     }  
57.   
58.     /* mterp setup */  
59.     LOGV("Using executionMode %d", gDvm.executionMode);  
60.     dvmCheckAsmConstants();  
61.   
62.     /* 
63.      * Initialize components. 
64.      */  
65.     dvmQuasiAtomicsStartup();  
66.     if (!dvmAllocTrackerStartup()) {  
67.         return "dvmAllocTrackerStartup failed";  
68.     }  
69.     if (!dvmGcStartup()) {  
70.         return "dvmGcStartup failed";  
71.     }  
72.     if (!dvmThreadStartup()) {  
73.         return "dvmThreadStartup failed";  
74.     }  
75.     if (!dvmInlineNativeStartup()) {  
76.         return "dvmInlineNativeStartup";  
77.     }  
78.     if (!dvmRegisterMapStartup()) {  
79.         return "dvmRegisterMapStartup failed";  
80.     }  
81.     if (!dvmInstanceofStartup()) {  
82.         return "dvmInstanceofStartup failed";  
83.     }  
84.     if (!dvmClassStartup()) {  
85.         return "dvmClassStartup failed";  
86.     }  
87.   
88.     /* 
89.      * At this point, the system is guaranteed to be sufficiently 
90.      * initialized that we can look up classes and class members. This 
91.      * call populates the gDvm instance with all the class and member 
92.      * references that the VM wants to use directly. 
93.      */  
94.     if (!dvmFindRequiredClassesAndMembers()) {  
95.         return "dvmFindRequiredClassesAndMembers failed";  
96.     }  
97.   
98.     if (!dvmStringInternStartup()) {  
99.         return "dvmStringInternStartup failed";  
100.     }  
101.     if (!dvmNativeStartup()) {  
102.         return "dvmNativeStartup failed";  
103.     }  
104.     if (!dvmInternalNativeStartup()) {  
105.         return "dvmInternalNativeStartup failed";  
106.     }  
107.     if (!dvmJniStartup()) {  
108.         return "dvmJniStartup failed";  
109.     }  
110.     if (!dvmProfilingStartup()) {  
111.         return "dvmProfilingStartup failed";  
112.     }  
113.   
114.     /* 
115.      * Create a table of methods for which we will substitute an "inline" 
116.      * version for performance. 
117.      */  
118.     if (!dvmCreateInlineSubsTable()) {  
119.         return "dvmCreateInlineSubsTable failed";  
120.     }  
121.   
122.     /* 
123.      * Miscellaneous class library validation. 
124.      */  
125.     if (!dvmValidateBoxClasses()) {  
126.         return "dvmValidateBoxClasses failed";  
127.     }  
128.   
129.     /* 
130.      * Do the last bits of Thread struct initialization we need to allow 
131.      * JNI calls to work. 
132.      */  
133.     if (!dvmPrepMainForJni(pEnv)) {  
134.         return "dvmPrepMainForJni failed";  
135.     }  
136.   
137.     /* 
138.      * Explicitly initialize java.lang.Class.  This doesn't happen 
139.      * automatically because it's allocated specially (it's an instance 
140.      * of itself).  Must happen before registration of system natives, 
141.      * which make some calls that throw assertions if the classes they 
142.      * operate on aren't initialized. 
143.      */  
144.     if (!dvmInitClass(gDvm.classJavaLangClass)) {  
145.         return "couldn't initialized java.lang.Class";  
146.     }  
147.   
148.     /* 
149.      * Register the system native methods, which are registered through JNI. 
150.      */  
151.     if (!registerSystemNatives(pEnv)) {  
152.         return "couldn't register system natives";  
153.     }  
154.   
155.     /* 
156.      * Do some "late" initialization for the memory allocator.  This may 
157.      * allocate storage and initialize classes. 
158.      */  
159.     if (!dvmCreateStockExceptions()) {  
160.         return "dvmCreateStockExceptions failed";  
161.     }  
162.   
163.     /* 
164.      * At this point, the VM is in a pretty good state.  Finish prep on 
165.      * the main thread (specifically, create a java.lang.Thread object to go 
166.      * along with our Thread struct).  Note we will probably be executing 
167.      * some interpreted class initializer code in here. 
168.      */  
169.     if (!dvmPrepMainThread()) {  
170.         return "dvmPrepMainThread failed";  
171.     }  
172.   
173.     /* 
174.      * Make sure we haven't accumulated any tracked references.  The main 
175.      * thread should be starting with a clean slate. 
176.      */  
177.     if (dvmReferenceTableEntries(&dvmThreadSelf()->internalLocalRefTable) != 0)  
178.     {  
179.         LOGW("Warning: tracked references remain post-initialization");  
180.         dvmDumpReferenceTable(&dvmThreadSelf()->internalLocalRefTable, "MAIN");  
181.     }  
182.   
183.     /* general debugging setup */  
184.     if (!dvmDebuggerStartup()) {  
185.         return "dvmDebuggerStartup failed";  
186.     }  
187.   
188.     if (!dvmGcStartupClasses()) {  
189.         return "dvmGcStartupClasses failed";  
190.     }  
191.   
192.     /* 
193.      * Init for either zygote mode or non-zygote mode.  The key difference 
194.      * is that we don't start any additional threads in Zygote mode. 
195.      */  
196.     if (gDvm.zygote) {  
197.         if (!initZygote()) {  
198.             return "initZygote failed";  
199.         }  
200.     } else {  
201.         if (!dvmInitAfterZygote()) {  
202.             return "dvmInitAfterZygote failed";  
203.         }  
204.     }  
205.   
206.   
207. #ifndef NDEBUG  
208.     if (!dvmTestHash())  
209.         LOGE("dvmTestHash FAILED");  
210.     if (false /*noisy!*/ && !dvmTestIndirectRefTable())  
211.         LOGE("dvmTestIndirectRefTable FAILED");  
212. #endif  
213.   
214.     if (dvmCheckException(dvmThreadSelf())) {  
215.         dvmLogExceptionStackTrace();  
216.         return "Exception pending at end of VM initialization";  
217.     }  
218.   
219.     scopedShutdown.disarm();  
220.     return "";  
221. }  

*
 * VM initialization.  Pass in any options provided on the command line.
 * Do not pass in the class name or the options for the class.
 *
 * Returns 0 on success.
 */
std::string dvmStartup(int argc, const char* const argv[],
        bool ignoreUnrecognized, JNIEnv* pEnv)
{
    ScopedShutdown scopedShutdown;

    assert(gDvm.initializing);

    LOGV("VM init args (%d):", argc);
    for (int i = 0; i < argc; i++) {
        LOGV("  %d: '%s'", i, argv[i]);
    }
    setCommandLineDefaults();

    /*
     * Process the option flags (if any).
     */
    int cc = processOptions(argc, argv, ignoreUnrecognized);
    if (cc != 0) {
        if (cc < 0) {
            dvmFprintf(stderr, "\n");
            usage("dalvikvm");
        }
        return "syntax error";
    }

#if WITH_EXTRA_GC_CHECKS > 1
    /* only "portable" interp has the extra goodies */
    if (gDvm.executionMode != kExecutionModeInterpPortable) {
        LOGI("Switching to 'portable' interpreter for GC checks");
        gDvm.executionMode = kExecutionModeInterpPortable;
    }
#endif

    /* Configure group scheduling capabilities */
    if (!access("/dev/cpuctl/tasks", F_OK)) {
        LOGV("Using kernel group scheduling");
        gDvm.kernelGroupScheduling = 1;
    } else {
        LOGV("Using kernel scheduler policies");
    }

    /* configure signal handling */
    if (!gDvm.reduceSignals)
        blockSignals();

    /* verify system page size */
    if (sysconf(_SC_PAGESIZE) != SYSTEM_PAGE_SIZE) {
        return StringPrintf("expected page size %d, got %d",
                SYSTEM_PAGE_SIZE, (int) sysconf(_SC_PAGESIZE));
    }

    /* mterp setup */
    LOGV("Using executionMode %d", gDvm.executionMode);
    dvmCheckAsmConstants();

    /*
     * Initialize components.
     */
    dvmQuasiAtomicsStartup();
    if (!dvmAllocTrackerStartup()) {
        return "dvmAllocTrackerStartup failed";
    }
    if (!dvmGcStartup()) {
        return "dvmGcStartup failed";
    }
    if (!dvmThreadStartup()) {
        return "dvmThreadStartup failed";
    }
    if (!dvmInlineNativeStartup()) {
        return "dvmInlineNativeStartup";
    }
    if (!dvmRegisterMapStartup()) {
        return "dvmRegisterMapStartup failed";
    }
    if (!dvmInstanceofStartup()) {
        return "dvmInstanceofStartup failed";
    }
    if (!dvmClassStartup()) {
        return "dvmClassStartup failed";
    }

    /*
     * At this point, the system is guaranteed to be sufficiently
     * initialized that we can look up classes and class members. This
     * call populates the gDvm instance with all the class and member
     * references that the VM wants to use directly.
     */
    if (!dvmFindRequiredClassesAndMembers()) {
        return "dvmFindRequiredClassesAndMembers failed";
    }

    if (!dvmStringInternStartup()) {
        return "dvmStringInternStartup failed";
    }
    if (!dvmNativeStartup()) {
        return "dvmNativeStartup failed";
    }
    if (!dvmInternalNativeStartup()) {
        return "dvmInternalNativeStartup failed";
    }
    if (!dvmJniStartup()) {
        return "dvmJniStartup failed";
    }
    if (!dvmProfilingStartup()) {
        return "dvmProfilingStartup failed";
    }

    /*
     * Create a table of methods for which we will substitute an "inline"
     * version for performance.
     */
    if (!dvmCreateInlineSubsTable()) {
        return "dvmCreateInlineSubsTable failed";
    }

    /*
     * Miscellaneous class library validation.
     */
    if (!dvmValidateBoxClasses()) {
        return "dvmValidateBoxClasses failed";
    }

    /*
     * Do the last bits of Thread struct initialization we need to allow
     * JNI calls to work.
     */
    if (!dvmPrepMainForJni(pEnv)) {
        return "dvmPrepMainForJni failed";
    }

    /*
     * Explicitly initialize java.lang.Class.  This doesn't happen
     * automatically because it's allocated specially (it's an instance
     * of itself).  Must happen before registration of system natives,
     * which make some calls that throw assertions if the classes they
     * operate on aren't initialized.
     */
    if (!dvmInitClass(gDvm.classJavaLangClass)) {
        return "couldn't initialized java.lang.Class";
    }

    /*
     * Register the system native methods, which are registered through JNI.
     */
    if (!registerSystemNatives(pEnv)) {
        return "couldn't register system natives";
    }

    /*
     * Do some "late" initialization for the memory allocator.  This may
     * allocate storage and initialize classes.
     */
    if (!dvmCreateStockExceptions()) {
        return "dvmCreateStockExceptions failed";
    }

    /*
     * At this point, the VM is in a pretty good state.  Finish prep on
     * the main thread (specifically, create a java.lang.Thread object to go
     * along with our Thread struct).  Note we will probably be executing
     * some interpreted class initializer code in here.
     */
    if (!dvmPrepMainThread()) {
        return "dvmPrepMainThread failed";
    }

    /*
     * Make sure we haven't accumulated any tracked references.  The main
     * thread should be starting with a clean slate.
     */
    if (dvmReferenceTableEntries(&dvmThreadSelf()->internalLocalRefTable) != 0)
    {
        LOGW("Warning: tracked references remain post-initialization");
        dvmDumpReferenceTable(&dvmThreadSelf()->internalLocalRefTable, "MAIN");
    }

    /* general debugging setup */
    if (!dvmDebuggerStartup()) {
        return "dvmDebuggerStartup failed";
    }

    if (!dvmGcStartupClasses()) {
        return "dvmGcStartupClasses failed";
    }

    /*
     * Init for either zygote mode or non-zygote mode.  The key difference
     * is that we don't start any additional threads in Zygote mode.
     */
    if (gDvm.zygote) {
        if (!initZygote()) {
            return "initZygote failed";
        }
    } else {
        if (!dvmInitAfterZygote()) {
            return "dvmInitAfterZygote failed";
        }
    }

#ifndef NDEBUG
    if (!dvmTestHash())
        LOGE("dvmTestHash FAILED");
    if (false /*noisy!*/ && !dvmTestIndirectRefTable())
        LOGE("dvmTestIndirectRefTable FAILED");
#endif

    if (dvmCheckException(dvmThreadSelf())) {
        dvmLogExceptionStackTrace();
        return "Exception pending at end of VM initialization";
    }

    scopedShutdown.disarm();
    return "";
}

 代码真长。寻找其中最具价值的部分

       

插入代码：

 

          

Java代码  

1. if (!dvmAllocTrackerStartup()) {  
2.      return "dvmAllocTrackerStartup failed";  
3.  }  
4.  if (!dvmGcStartup()) {  
5.      return "dvmGcStartup failed";  
6.  }  
7.  if (!dvmThreadStartup()) {  
8.      return "dvmThreadStartup failed";  
9.  }  
10.  if (!dvmInlineNativeStartup()) {  
11.      return "dvmInlineNativeStartup";  
12.  }  
13.  if (!dvmRegisterMapStartup()) {  
14.      return "dvmRegisterMapStartup failed";  
15.  }  
16.  if (!dvmInstanceofStartup()) {  
17.      return "dvmInstanceofStartup failed";  
18.  }  
19.  if (!dvmClassStartup()) {  
20.      return "dvmClassStartup failed";  
21.  }  

   if (!dvmAllocTrackerStartup()) {
        return "dvmAllocTrackerStartup failed";
    }
    if (!dvmGcStartup()) {
        return "dvmGcStartup failed";
    }
    if (!dvmThreadStartup()) {
        return "dvmThreadStartup failed";
    }
    if (!dvmInlineNativeStartup()) {
        return "dvmInlineNativeStartup";
    }
    if (!dvmRegisterMapStartup()) {
        return "dvmRegisterMapStartup failed";
    }
    if (!dvmInstanceofStartup()) {
        return "dvmInstanceofStartup failed";
    }
    if (!dvmClassStartup()) {
        return "dvmClassStartup failed";
    }

 经分析，这些都没有建立gc线程，gc线程的建立是在如下方法：

 

 

Java代码  

1. dvmInitAfterZygote  

dvmInitAfterZygote

 

  由于跟得太深，东西很多，就不一一列举。仅仅跟一下dvmClassStartup，最终调用到了dalvik/vm/oo/Class.cpp中的方法：

 

Java代码  

1. /* 
2.  * Initialize the bootstrap class loader. 
3.  * 
4.  * Call this after the bootclasspath string has been finalized. 
5.  */  
6. bool dvmClassStartup()  
7. {  
8.     /* make this a requirement -- don't currently support dirs in path */  
9.     if (strcmp(gDvm.bootClassPathStr, ".") == 0) {  
10.         LOGE("ERROR: must specify non-'.' bootclasspath");  
11.         return false;  
12.     }  
13.   
14.     gDvm.loadedClasses =  
15.         dvmHashTableCreate(256, (HashFreeFunc) dvmFreeClassInnards);  
16.   
17.     gDvm.pBootLoaderAlloc = dvmLinearAllocCreate(NULL);  
18.     if (gDvm.pBootLoaderAlloc == NULL)  
19.         return false;  
20.   
21.     if (false) {  
22.         linearAllocTests();  
23.         exit(0);  
24.     }  
25.   
26.     /* 
27.      * Class serial number.  We start with a high value to make it distinct 
28.      * in binary dumps (e.g. hprof). 
29.      */  
30.     gDvm.classSerialNumber = INITIAL_CLASS_SERIAL_NUMBER;  
31.   
32.     /* 
33.      * Set up the table we'll use for tracking initiating loaders for 
34.      * early classes. 
35.      * If it's NULL, we just fall back to the InitiatingLoaderList in the 
36.      * ClassObject, so it's not fatal to fail this allocation. 
37.      */  
38.     gDvm.initiatingLoaderList = (InitiatingLoaderList*)  
39.         calloc(ZYGOTE_CLASS_CUTOFF, sizeof(InitiatingLoaderList));  
40.   
41.     /* 
42.      * Create the initial classes. These are the first objects constructed 
43.      * within the nascent VM. 
44.      */  
45.     if (!createInitialClasses()) {  
46.         return false;  
47.     }  
48.   
49.     /* 
50.      * Process the bootstrap class path.  This means opening the specified 
51.      * DEX or Jar files and possibly running them through the optimizer. 
52.      */  
53.     assert(gDvm.bootClassPath == NULL);  
54.     processClassPath(gDvm.bootClassPathStr, true);  
55.   
56.     if (gDvm.bootClassPath == NULL)  
57.         return false;  
58.   
59.     return true;  
60. }  

/*
 * Initialize the bootstrap class loader.
 *
 * Call this after the bootclasspath string has been finalized.
 */
bool dvmClassStartup()
{
    /* make this a requirement -- don't currently support dirs in path */
    if (strcmp(gDvm.bootClassPathStr, ".") == 0) {
        LOGE("ERROR: must specify non-'.' bootclasspath");
        return false;
    }

    gDvm.loadedClasses =
        dvmHashTableCreate(256, (HashFreeFunc) dvmFreeClassInnards);

    gDvm.pBootLoaderAlloc = dvmLinearAllocCreate(NULL);
    if (gDvm.pBootLoaderAlloc == NULL)
        return false;

    if (false) {
        linearAllocTests();
        exit(0);
    }

    /*
     * Class serial number.  We start with a high value to make it distinct
     * in binary dumps (e.g. hprof).
     */
    gDvm.classSerialNumber = INITIAL_CLASS_SERIAL_NUMBER;

    /*
     * Set up the table we'll use for tracking initiating loaders for
     * early classes.
     * If it's NULL, we just fall back to the InitiatingLoaderList in the
     * ClassObject, so it's not fatal to fail this allocation.
     */
    gDvm.initiatingLoaderList = (InitiatingLoaderList*)
        calloc(ZYGOTE_CLASS_CUTOFF, sizeof(InitiatingLoaderList));

    /*
     * Create the initial classes. These are the first objects constructed
     * within the nascent VM.
     */
    if (!createInitialClasses()) {
        return false;
    }

    /*
     * Process the bootstrap class path.  This means opening the specified
     * DEX or Jar files and possibly running them through the optimizer.
     */
    assert(gDvm.bootClassPath == NULL);
    processClassPath(gDvm.bootClassPathStr, true);

    if (gDvm.bootClassPath == NULL)
        return false;

    return true;
}

 根据注释，Initialize the bootstrap class loader.
这个函数告诉我们，他建立了boottrap classloader。

createInitialClasses加载了9大基本类型。而后的processClassPath则建立了基本的classloader。分析过后，比较失望。可能是为后续的boottrapclassloader做一些前期准备工作。

startVM就到这里。

 

好吧。现在又回到了最初的App_main.cpp中。进入了com.android.internal.os.ZygoteInit.java的main

 

Java代码  

1. public static void main(String argv[]) {  
2.     try {  
3.         // Start profiling the zygote initialization.  
4.         SamplingProfilerIntegration.start();  
5.   
6.         registerZygoteSocket();  
7.         EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START,  
8.             SystemClock.uptimeMillis());  
9.         preload();  
10.         EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_END,  
11.             SystemClock.uptimeMillis());  
12.   
13.         // Finish profiling the zygote initialization.  
14.         SamplingProfilerIntegration.writeZygoteSnapshot();  
15.   
16.         // Do an initial gc to clean up after startup  
17.         gc();  
18.   
19.         // If requested, start system server directly from Zygote  
20.         if (argv.length != 2) {  
21.             throw new RuntimeException(argv[0] + USAGE_STRING);  
22.         }  
23.   
24.         if (argv[1].equals("start-system-server")) {  
25.             startSystemServer();  
26.         } else if (!argv[1].equals("")) {  
27.             throw new RuntimeException(argv[0] + USAGE_STRING);  
28.         }  
29.   
30.         Log.i(TAG, "Accepting command socket connections");  
31.   
32.         if (ZYGOTE_FORK_MODE) {  
33.             runForkMode();  
34.         } else {  
35.             runSelectLoopMode();  
36.         }  
37.   
38.         closeServerSocket();  
39.     } catch (MethodAndArgsCaller caller) {  
40.         caller.run();  
41.     } catch (RuntimeException ex) {  
42.         Log.e(TAG, "Zygote died with exception", ex);  
43.         closeServerSocket();  
44.         throw ex;  
45.     }  
46. }  

    public static void main(String argv[]) {
        try {
            // Start profiling the zygote initialization.
            SamplingProfilerIntegration.start();

            registerZygoteSocket();
            EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START,
                SystemClock.uptimeMillis());
            preload();
            EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_END,
                SystemClock.uptimeMillis());

            // Finish profiling the zygote initialization.
            SamplingProfilerIntegration.writeZygoteSnapshot();

            // Do an initial gc to clean up after startup
            gc();

            // If requested, start system server directly from Zygote
            if (argv.length != 2) {
                throw new RuntimeException(argv[0] + USAGE_STRING);
            }

            if (argv[1].equals("start-system-server")) {
                startSystemServer();
            } else if (!argv[1].equals("")) {
                throw new RuntimeException(argv[0] + USAGE_STRING);
            }

            Log.i(TAG, "Accepting command socket connections");

            if (ZYGOTE_FORK_MODE) {
                runForkMode();
            } else {
                runSelectLoopMode();
            }

            closeServerSocket();
        } catch (MethodAndArgsCaller caller) {
            caller.run();
        } catch (RuntimeException ex) {
            Log.e(TAG, "Zygote died with exception", ex);
            closeServerSocket();
            throw ex;
        }
    }

 

 

 回过头来继续看一下ZygoteInit.java这个类是如何初始化的，看如下代码：

Java代码  

1. /* 
2.  * Create a new JNIEnv struct and add it to the VM's list. 
3.  * 
4.  * "self" will be NULL for the main thread, since the VM hasn't started 
5.  * yet; the value will be filled in later. 
6.  */  
7. JNIEnv* dvmCreateJNIEnv(Thread* self) {  
8.     JavaVMExt* vm = (JavaVMExt*) gDvmJni.jniVm;  
9.   
10.     //if (self != NULL)  
11.     //    LOGI("Ent CreateJNIEnv: threadid=%d %p", self->threadId, self);  
12.   
13.     assert(vm != NULL);  
14.   
15.     JNIEnvExt* newEnv = (JNIEnvExt*) calloc(1, sizeof(JNIEnvExt));  
16.     newEnv->funcTable = &gNativeInterface;  
17.     if (self != NULL) {  
18.         dvmSetJniEnvThreadId((JNIEnv*) newEnv, self);  
19.         assert(newEnv->envThreadId != 0);  
20.     } else {  
21.         /* make it obvious if we fail to initialize these later */  
22.         newEnv->envThreadId = 0x77777775;  
23.         newEnv->self = (Thread*) 0x77777779;  
24.     }  
25.     if (gDvmJni.useCheckJni) {  
26.         dvmUseCheckedJniEnv(newEnv);  
27.     }  
28.   
29.     ScopedPthreadMutexLock lock(&vm->envListLock);  
30.   
31.     /* insert at head of list */  
32.     newEnv->next = vm->envList;  
33.     assert(newEnv->prev == NULL);  
34.     if (vm->envList == NULL) {  
35.         // rare, but possible  
36.         vm->envList = newEnv;  
37.     } else {  
38.         vm->envList->prev = newEnv;  
39.     }  
40.     vm->envList = newEnv;  
41.   
42.     //if (self != NULL)  
43.     //    LOGI("Xit CreateJNIEnv: threadid=%d %p", self->threadId, self);  
44.     return (JNIEnv*) newEnv;  
45. }  

/*
 * Create a new JNIEnv struct and add it to the VM's list.
 *
 * "self" will be NULL for the main thread, since the VM hasn't started
 * yet; the value will be filled in later.
 */
JNIEnv* dvmCreateJNIEnv(Thread* self) {
    JavaVMExt* vm = (JavaVMExt*) gDvmJni.jniVm;

    //if (self != NULL)
    //    LOGI("Ent CreateJNIEnv: threadid=%d %p", self->threadId, self);

    assert(vm != NULL);

    JNIEnvExt* newEnv = (JNIEnvExt*) calloc(1, sizeof(JNIEnvExt));
    newEnv->funcTable = &gNativeInterface;
    if (self != NULL) {
        dvmSetJniEnvThreadId((JNIEnv*) newEnv, self);
        assert(newEnv->envThreadId != 0);
    } else {
        /* make it obvious if we fail to initialize these later */
        newEnv->envThreadId = 0x77777775;
        newEnv->self = (Thread*) 0x77777779;
    }
    if (gDvmJni.useCheckJni) {
        dvmUseCheckedJniEnv(newEnv);
    }

    ScopedPthreadMutexLock lock(&vm->envListLock);

    /* insert at head of list */
    newEnv->next = vm->envList;
    assert(newEnv->prev == NULL);
    if (vm->envList == NULL) {
        // rare, but possible
        vm->envList = newEnv;
    } else {
        vm->envList->prev = newEnv;
    }
    vm->envList = newEnv;

    //if (self != NULL)
    //    LOGI("Xit CreateJNIEnv: threadid=%d %p", self->threadId, self);
    return (JNIEnv*) newEnv;
}

 

 

 

 最重要的是gNativeInterface 我们看定义，太长了，我们找到其中的FindClass。

 

Cpp代码  

1. static jclass FindClass(JNIEnv* env, const char* name) {  
2.     ScopedJniThreadState ts(env);  
3.   
4.     const Method* thisMethod = dvmGetCurrentJNIMethod();  
5.     assert(thisMethod != NULL);  
6.   
7.     Object* loader;  
8.     Object* trackedLoader = NULL;  
9.     if (ts.self()->classLoaderOverride != NULL) {  
10.         /* hack for JNI_OnLoad */  
11.         assert(strcmp(thisMethod->name, "nativeLoad") == 0);  
12.         loader = ts.self()->classLoaderOverride;  
13.     } else if (thisMethod == gDvm.methDalvikSystemNativeStart_main ||  
14.                thisMethod == gDvm.methDalvikSystemNativeStart_run) {  
15.         /* start point of invocation interface */  
16.         if (!gDvm.initializing) {  
17.             loader = trackedLoader = dvmGetSystemClassLoader();  
18.         } else {  
19.             loader = NULL;  
20.         }  
21.     } else {  
22.         loader = thisMethod->clazz->classLoader;  
23.     }  
24.   
25.     char* descriptor = dvmNameToDescriptor(name);  
26.     if (descriptor == NULL) {  
27.         return NULL;  
28.     }  
29.     ClassObject* clazz = dvmFindClassNoInit(descriptor, loader);  
30.     free(descriptor);  
31.   
32.     jclass jclazz = (jclass) addLocalReference(ts.self(), (Object*) clazz);  
33.     dvmReleaseTrackedAlloc(trackedLoader, ts.self());  
34.     return jclazz;  
35. }  

static jclass FindClass(JNIEnv* env, const char* name) {
    ScopedJniThreadState ts(env);

    const Method* thisMethod = dvmGetCurrentJNIMethod();
    assert(thisMethod != NULL);

    Object* loader;
    Object* trackedLoader = NULL;
    if (ts.self()->classLoaderOverride != NULL) {
        /* hack for JNI_OnLoad */
        assert(strcmp(thisMethod->name, "nativeLoad") == 0);
        loader = ts.self()->classLoaderOverride;
    } else if (thisMethod == gDvm.methDalvikSystemNativeStart_main ||
               thisMethod == gDvm.methDalvikSystemNativeStart_run) {
        /* start point of invocation interface */
        if (!gDvm.initializing) {
            loader = trackedLoader = dvmGetSystemClassLoader();
        } else {
            loader = NULL;
        }
    } else {
        loader = thisMethod->clazz->classLoader;
    }

    char* descriptor = dvmNameToDescriptor(name);
    if (descriptor == NULL) {
        return NULL;
    }
    ClassObject* clazz = dvmFindClassNoInit(descriptor, loader);
    free(descriptor);

    jclass jclazz = (jclass) addLocalReference(ts.self(), (Object*) clazz);
    dvmReleaseTrackedAlloc(trackedLoader, ts.self());
    return jclazz;
}

 

 

在dalvik/vm/Init.cpp中的方法对gVM的bootpath进行了初始化：

 

 

Java代码  

1. static void setCommandLineDefaults()  
2. {  
3.     const char* envStr = getenv("CLASSPATH");  
4.     if (envStr != NULL) {  
5.         gDvm.classPathStr = strdup(envStr);  
6.     } else {  
7.         gDvm.classPathStr = strdup(".");  
8.     }  
9.     envStr = getenv("BOOTCLASSPATH");  
10.     if (envStr != NULL) {  
11.         gDvm.bootClassPathStr = strdup(envStr);  
12.     } else {  
13.         gDvm.bootClassPathStr = strdup(".");  
14.     }  
15.   
16.     gDvm.properties = new std::vector<std::string>();  
17.   
18.     /* Defaults overridden by -Xms and -Xmx. 
19.      * TODO: base these on a system or application-specific default 
20.      */  
21.     gDvm.heapStartingSize = 2 * 1024 * 1024;  // Spec says 16MB; too big for us.  
22.     gDvm.heapMaximumSize = 16 * 1024 * 1024;  // Spec says 75% physical mem  
23.     gDvm.heapGrowthLimit = 0;  // 0 means no growth limit  
24.     gDvm.stackSize = kDefaultStackSize;  
25.   
26.     gDvm.concurrentMarkSweep = true;  
27.   
28.     /* gDvm.jdwpSuspend = true; */  

static void setCommandLineDefaults()
{
    const char* envStr = getenv("CLASSPATH");
    if (envStr != NULL) {
        gDvm.classPathStr = strdup(envStr);
    } else {
        gDvm.classPathStr = strdup(".");
    }
    envStr = getenv("BOOTCLASSPATH");
    if (envStr != NULL) {
        gDvm.bootClassPathStr = strdup(envStr);
    } else {
        gDvm.bootClassPathStr = strdup(".");
    }

    gDvm.properties = new std::vector<std::string>();

    /* Defaults overridden by -Xms and -Xmx.
     * TODO: base these on a system or application-specific default
     */
    gDvm.heapStartingSize = 2 * 1024 * 1024;  // Spec says 16MB; too big for us.
    gDvm.heapMaximumSize = 16 * 1024 * 1024;  // Spec says 75% physical mem
    gDvm.heapGrowthLimit = 0;  // 0 means no growth limit
    gDvm.stackSize = kDefaultStackSize;

    gDvm.concurrentMarkSweep = true;

    /* gDvm.jdwpSuspend = true; */

 

现在明白了，在init.rc中指定的BOOTCLASSPATH赋值给了gDvm.bootClassPathStr 。

而下面这个地方，则对FindClass进行了初始化。还是在dalvik/vm/Init.cpp中

Cpp代码  

1. */  
2. f (!dvmFindRequiredClassesAndMembers()) {  
3.    return "dvmFindRequiredClassesAndMembers failed";  

     */
    if (!dvmFindRequiredClassesAndMembers()) {
        return "dvmFindRequiredClassesAndMembers failed";
    }

initDirectMethodReferences 把方法gDvm.methDalvikSystemNativeStart_main与NativeStart进行了对应。

Java代码  

1. { &gDvm.methDalvikSystemNativeStart_main, "Ldalvik/system/NativeStart;", "main", "([Ljava/lang/String;)V" },  

 { &gDvm.methDalvikSystemNativeStart_main, "Ldalvik/system/NativeStart;", "main", "([Ljava/lang/String;)V" },

 

主要分析FindClass方法：

 nativeLoad标示从System.loadlibrary加载。那么Zygote的dvmGetCurrentJNIMethod是哪个呢。我猜测，这个一定是没有的，也就是里面的成员变量全为空。哈哈。这意味着，最终调用到了

dvmFindClassNoInit方法中。

然后是ClassObject* dvmFindSystemClassNoInit(const char* descriptor)
{
    return findClassNoInit(descriptor, NULL, NULL);
}
然后是findClassNoInit

ZygoteInit这个类根本是没有ClassLoader的。而是直接从包里面查找得到的。

进入ZygoteInit后。就是java代码了。