Android-Native-Server 启动和注册详细分析
以mediaService为实例来讲解:
mediaService的启动入口 是一个 传统的 main()函数
源码位置E:\src_android\android_4.1.1_r1\android_4.1.1_r1\frameworks\av\media\mediaserver\main_mediaserver.cpp
步骤:、
1.获取ProcessState实例的强引用 proc
2.获取到一个BpServiceManager ServiceManager的代理类
3.初始化服务:AudioFlinger MediaPlayerService CameraService AudioPolicyService
4.开启线程池
int main(int argc, char** argv)
{
//sp 是 strongpointer 是一个强引用指针
//获取ProcessState实例的强引用
sp<ProcessState> proc(ProcessState::self());
//获取到一个BpServiceManager(BpBinder的子类)(servicerManager的代理对象)
sp<IServiceManager> sm = defaultServiceManager();
ALOGI("ServiceManager: %p", sm.get());
//AudioFlinger服务初始化
AudioFlinger::instantiate();
//MediaPlayerService服务初始化
MediaPlayerService::instantiate();
//CameraService服务初始化
CameraService::instantiate();
//AudioPolicyService服务初始化
AudioPolicyService::instantiate();
//Server进程开启线程池 ?
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
}
{
//sp 是 strongpointer 是一个强引用指针
//获取ProcessState实例的强引用
sp<ProcessState> proc(ProcessState::self());
//获取到一个BpServiceManager(BpBinder的子类)(servicerManager的代理对象)
sp<IServiceManager> sm = defaultServiceManager();
ALOGI("ServiceManager: %p", sm.get());
//AudioFlinger服务初始化
AudioFlinger::instantiate();
//MediaPlayerService服务初始化
MediaPlayerService::instantiate();
//CameraService服务初始化
CameraService::instantiate();
//AudioPolicyService服务初始化
AudioPolicyService::instantiate();
//Server进程开启线程池 ?
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
}
2.(callby 1) ProcessState::self()是一个单例模式,第一次调用时,gProcess == null 会出发ProcessState的构造函数
源码位置E:\src_android\android_4.1.1_r1\android_4.1.1_r1\frameworks\native\libs\binder\ProcessState.cpp
sp<ProcessState> ProcessState::self()
{
Mutex::Autolock _l(gProcessMutex);
if (gProcess != NULL) {
return gProcess;
}
gProcess = new ProcessState;
return gProcess;
}
{
Mutex::Autolock _l(gProcessMutex);
if (gProcess != NULL) {
return gProcess;
}
gProcess = new ProcessState;
return gProcess;
}
3.(callby 2) ProcessState的实例化会打开Binder设备并进行内存映射。
源码位置E:\src_android\android_4.1.1_r1\android_4.1.1_r1\frameworks\native\libs\binder\ProcessState.cpp
ProcessState)
{
) {, BINDER_VM_SIZE, PROT_READ, MAP_PRIVATE );
;
}
#;
#endif
}
LOG_ALWAYS_FATAL
{
) {, BINDER_VM_SIZE, PROT_READ, MAP_PRIVATE );
;
}
#;
#endif
}
LOG_ALWAYS_FATAL
4.(callby 3)Binder设备的打开函数。用来打开Binder设备。
源码位置E:\src_android\android_4.1.1_r1\android_4.1.1_r1\frameworks\native\libs\binder\ProcessState.cpp
) {
) {
ALOGE(;
}
;
}
;
result ) {
ALOGE("Binder ioctl to set max threads failed: %s", strerror(errno));
}
} else {
ALOGW("Opening '/dev/binder' failed: %s\n", strerror(errno));
}
return fd;
}
) {
ALOGE(;
}
;
}
;
result ) {
ALOGE("Binder ioctl to set max threads failed: %s", strerror(errno));
}
} else {
ALOGW("Opening '/dev/binder' failed: %s\n", strerror(errno));
}
return fd;
}
5.(callby 1) 返回一个BpServiceMamager.是ServiceManager的代理类。
源码位置:IServiceManager.cpp
interface_cast是一个复杂的宏定义把BpBidner封装成BpServiceManager,BpBidner存储在BpServiceManager父类的 BpRefBase 中的mRemote 中并提供remote()函数来返回BpBidner变量
sp<IServiceManager> defaultServiceManager()
{
if (gDefaultServiceManager != NULL) return gDefaultServiceManager;
{
AutoMutex _l(gDefaultServiceManagerLock);
if (gDefaultServiceManager == NULL) {
gDefaultServiceManager = interface_cast<IServiceManager>(
ProcessState::self()->getContextObject(NULL));
}//ProcessState::self()单例函数调用,getContextObject返回的是一个BpBidner
//interface_cast<IServiceManager> 函数把BpBidner封装成BpServiceManager,BpBidner被放在
//BpServiceManager父类的 BpRefBase 中的mRemote 中并提供remote()函数来返回BpBidner变量
}
return gDefaultServiceManager;
}
{
if (gDefaultServiceManager != NULL) return gDefaultServiceManager;
{
AutoMutex _l(gDefaultServiceManagerLock);
if (gDefaultServiceManager == NULL) {
gDefaultServiceManager = interface_cast<IServiceManager>(
ProcessState::self()->getContextObject(NULL));
}//ProcessState::self()单例函数调用,getContextObject返回的是一个BpBidner
//interface_cast<IServiceManager> 函数把BpBidner封装成BpServiceManager,BpBidner被放在
//BpServiceManager父类的 BpRefBase 中的mRemote 中并提供remote()函数来返回BpBidner变量
}
return gDefaultServiceManager;
}
AudioFlinger::instantiate();这一句是对AudioFlinger的初始化(下面的MediaPlayerService等也是同个道理)
AudioFlinger继承了BinderService<AudioFlinger> 和BnAudioFlinger
Binder<AudioFlinger> 提供了两个静态函数在这里被用到
instantiate 和 publish,publish被instantiate简单调用而已。
源码:BinderService.h
template<typename SERVICE>
class BinderService
{
public:
//调用了IServiceManager的addService方法,实现服务的注册
static status_t publish(bool allowIsolated = false) {
sp<IServiceManager> sm(defaultServiceManager());
return sm->addService(String16(SERVICE::getServiceName()), new SERVICE(), allowIsolated);
}
static void publishAndJoinThreadPool(bool allowIsolated = false) {
sp<IServiceManager> sm(defaultServiceManager());
sm->addService(String16(SERVICE::getServiceName()), new SERVICE(), allowIsolated);
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
}
//简单调用了publish()方法。
static void instantiate() { publish(); }
static status_t shutdown() {
return NO_ERROR;
}
};
class BinderService
{
public:
//调用了IServiceManager的addService方法,实现服务的注册
static status_t publish(bool allowIsolated = false) {
sp<IServiceManager> sm(defaultServiceManager());
return sm->addService(String16(SERVICE::getServiceName()), new SERVICE(), allowIsolated);
}
static void publishAndJoinThreadPool(bool allowIsolated = false) {
sp<IServiceManager> sm(defaultServiceManager());
sm->addService(String16(SERVICE::getServiceName()), new SERVICE(), allowIsolated);
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
}
//简单调用了publish()方法。
static void instantiate() { publish(); }
static status_t shutdown() {
return NO_ERROR;
}
};
publish中调用了人 defaultServiceManager。获取到serviceManager。
在Android的Binder框架中,可以说有三种C/S模式:
1.Client:serviceManager Server: Binder设备驱动
2.Client:AudioFlinger Server: serviceManager
3.Client:用户 Server: AudioFlinger
下面publish是第一种C/S模型,实现了serviceManage和Binder设备驱动的交互。通过 sm - > addService提交事务。
static status_t publish( bool allowIsolated = false ) {
sp < IServiceManager > sm(defaultServiceManager());
return sm - > addService(String16(SERVICE : : getServiceName()), new SERVICE(), allowIsolated);
}
sp < IServiceManager > sm(defaultServiceManager());
return sm - > addService(String16(SERVICE : : getServiceName()), new SERVICE(), allowIsolated);
}
下面是sm->addservice的具体实现:
Parcel是进程之间通信用的数据格式,data是client传给server的数据,reply是存储Server处理后返回的结果数据。
IServiceManager::getInterfaceDescriptor());是由宏实现的,返回的是"android.os.IserviceManager"
name是当前服务名称"media.audio_fligner"
service:是AudioFlinger实例
remote()返回的是BpBinder实例
);
//调用remote()返回一个IBinder对象,在调用BpBinder的事物处理函数transact
//来处理这个事物
status_t err = remote()->transact(ADD_SERVICE_TRANSACTION, data, &reply);
return err == NO_ERROR ? reply.readExceptionCode() : err;
}
//调用remote()返回一个IBinder对象,在调用BpBinder的事物处理函数transact
//来处理这个事物
status_t err = remote()->transact(ADD_SERVICE_TRANSACTION, data, &reply);
return err == NO_ERROR ? reply.readExceptionCode() : err;
}
transact中调用了 IPCThreadState::self()->transact,真正对事务进行处理是在IPCThreadState中进行的。
源码:BpBinder.cpp
status_t BpBinder;
return status;
}
return DEAD_OBJECT;
}
return status;
}
return DEAD_OBJECT;
}
IPCThreadState::transact中有两个重要的函数:
writeTransactionData 和 waitForResponse
writeTransactionData :负责对与Binder设备通讯的数据进行封装。
waitForResponse:负责与Binder设备通讯,还有返回数据的封装。
status_t IPCThreadState ? "READ REPLY" : "ONE WAY");
err = writeTransactionData(BC_TRANSACTION, flags, handle, code, data, NULL);
}
..............
err = writeTransactionData(BC_TRANSACTION, flags, handle, code, data, NULL);
}
..............
........省略部分代码.........
...............
if (reply) {
err = waitForResponse(reply);
} else {
Parcel fakeReply;
err = waitForResponse(&fakeReply);
}
..............
if (reply) {
err = waitForResponse(reply);
} else {
Parcel fakeReply;
err = waitForResponse(&fakeReply);
}
..............
.........省略部分代码.........
...............
return err;
}
return err;
}
writeTransactionData 顾名思义就是写入事务所需要的数据。
与Binder设备进行数据的交互是另外一种数据结构binder_transaction_data,不同于进程之间进行通讯的数据结构Parcel
与Binder设备进行数据的交互是另外一种数据结构binder_transaction_data,不同于进程之间进行通讯的数据结构Parcel
所以在这里就必须把Parcel转换成binder_transaction_data 。
最终是把binder_transaction_data 写进ServiceManager进程在Binder设备申请的内存映射区mOut里面。
上面就把要给Binder设备的数据封装好,放在一个Binder知道的地方。
接下来,就要让Binder去取数据,并做处理。
status_t IPCThreadState;
tr.sender_pid ;
tr.sender_euid ;
;
tr.data.ptr.offsets = NULL;
} else {
return (mLastError = err);
}
mOut.writeInt32(cmd);
mOut.write(&tr, sizeof(tr));
return NO_ERROR;
tr.sender_pid ;
tr.sender_euid ;
;
tr.data.ptr.offsets = NULL;
} else {
return (mLastError = err);
}
mOut.writeInt32(cmd);
mOut.write(&tr, sizeof(tr));
return NO_ERROR;
waitForResponse是另一个重要函数,里面有一个while循环,每次循环的开始都会执行talkWithDriver函数,然后去读取 cmd = mIn.readInt32(); 其返回的是一个command,意思是通过talkWithDriver不断地去访问Binder设备,“催促Binder设备快点处理我的事务”,然后通过mIn.readInt32()得到事务处理结果,再用swich语句来处理,Binder反馈回来的结果,其中case BR_REPLY:是我们最终想要得到的反馈结果,意思是Binder已经对我们的事务做了处理,并有结果了,在这个分支里面,我们把结果写进Parcel *reply,并通过go finish结束函数。
status_t IPCThreadState) {
) ) {
reply->ipcSetDataReference(
reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer),
tr.data_size,
reinterpret_cast<const size_t*>(tr.data.ptr.offsets),
tr.offsets_size/sizeof(size_t),
freeBuffer, this);
} else {
err = *static_cast<const status_t*>(tr.data.ptr.buffer);
freeBuffer(NULL,
reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer),
tr.data_size,
reinterpret_cast<const size_t*>(tr.data.ptr.offsets),
tr.offsets_size/sizeof(size_t), this);
}
} else {
freeBuffer(NULL,
reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer),
tr.data_size,
reinterpret_cast<const size_t*>(tr.data.ptr.offsets),
tr.offsets_size/sizeof(size_t), this);
continue;
}
}
goto finish;
default:
err = executeCommand(cmd);
if (err != NO_ERROR) goto finish;
break;
}
}
finish:
if (err != NO_ERROR) {
if (acquireResult) *acquireResult = err;
if (reply) reply->setError(err);
mLastError = err;
}
return err;
}
) ) {
reply->ipcSetDataReference(
reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer),
tr.data_size,
reinterpret_cast<const size_t*>(tr.data.ptr.offsets),
tr.offsets_size/sizeof(size_t),
freeBuffer, this);
} else {
err = *static_cast<const status_t*>(tr.data.ptr.buffer);
freeBuffer(NULL,
reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer),
tr.data_size,
reinterpret_cast<const size_t*>(tr.data.ptr.offsets),
tr.offsets_size/sizeof(size_t), this);
}
} else {
freeBuffer(NULL,
reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer),
tr.data_size,
reinterpret_cast<const size_t*>(tr.data.ptr.offsets),
tr.offsets_size/sizeof(size_t), this);
continue;
}
}
goto finish;
default:
err = executeCommand(cmd);
if (err != NO_ERROR) goto finish;
break;
}
}
finish:
if (err != NO_ERROR) {
if (acquireResult) *acquireResult = err;
if (reply) reply->setError(err);
mLastError = err;
}
return err;
}
talkWithDriver中进行内核的Binder通信。
关键函数是:ioctl(mProcess->mDriverFD, BINDER_WRITE_READ, &bwr) 进行系统调用。
最后把返回的数据写进 mIn 。
mIn.setDataSize(bwr.read_consumed);
mIn.setDataPosition(0);
mIn.setDataPosition(0);
status_t IPCThreadState, ;
bwr.write_size ;
bwr.read_buffer ;
}
) {
alog ) )) ;
bwr.read_consumed ;
status_t err;
)
err ) {
, bwr.write_consumed);
);
}
) {
mIn.setDataSize(bwr.read_consumed);
mIn.setDataPosition();
}
IF_LOG_COMMANDS() {
TextOutput::Bundle _b(alog);
alog << "Remaining data size: " << mOut.dataSize() << endl;
alog << "Received commands from driver: " << indent;
const void* cmds = mIn.data();
const void* end = mIn.data() + mIn.dataSize();
alog << HexDump(cmds, mIn.dataSize()) << endl;
while (cmds < end) cmds = printReturnCommand(alog, cmds);
alog << dedent;
}
return NO_ERROR;
}
return err;
}
bwr.write_size ;
bwr.read_buffer ;
}
) {
alog ) )) ;
bwr.read_consumed ;
status_t err;
)
err ) {
, bwr.write_consumed);
);
}
) {
mIn.setDataSize(bwr.read_consumed);
mIn.setDataPosition();
}
IF_LOG_COMMANDS() {
TextOutput::Bundle _b(alog);
alog << "Remaining data size: " << mOut.dataSize() << endl;
alog << "Received commands from driver: " << indent;
const void* cmds = mIn.data();
const void* end = mIn.data() + mIn.dataSize();
alog << HexDump(cmds, mIn.dataSize()) << endl;
while (cmds < end) cmds = printReturnCommand(alog, cmds);
alog << dedent;
}
return NO_ERROR;
}
return err;
}
最后是开启线程池:
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
IPCThreadState::self()->joinThreadPool();
startThreadPool:
mThreadPoolStarted = true;设置当前线程池的启动标志。
spawnPooledThread中开启一个新线程sp<Thread> t = new PoolThread(isMain);//PoolThread是Thread的子类。
并执行线程函数来运行线程 t->run(buf);
最后IPCThreadState::self()->joinThreadPool();把主线程也加入了线程池。!!!
void ProcessState::startThreadPool()
{
AutoMutex _l(mLock);
if (!mThreadPoolStarted) {
mThreadPoolStarted = true;
spawnPooledThread(true);
}
}
{
AutoMutex _l(mLock);
if (!mThreadPoolStarted) {
mThreadPoolStarted = true;
spawnPooledThread(true);
}
}
void ProcessState::spawnPooledThread(bool isMain)
{
if (mThreadPoolStarted) {
int32_t s = android_atomic_add(1, &mThreadPoolSeq);
char buf[16];
snprintf(buf, sizeof(buf), "Binder_%X", s);
ALOGV("Spawning new pooled thread, name=%s\n", buf);
sp<Thread> t = new PoolThread(isMain);
t->run(buf);
}
}
上面提到的宏定义及其实现:
#define DECLARE_META_INTERFACE(INTERFACE) \
static const android::String16 descriptor; \
static android::sp<I##INTERFACE> asInterface( \
const android::sp<android::IBinder>& obj); \
virtual const android::String16& getInterfaceDescriptor() const; \
I##INTERFACE(); \
virtual ~I##INTERFACE(); \
#define IMPLEMENT_META_INTERFACE(INTERFACE, NAME) \
const android::String16 I##INTERFACE::descriptor(NAME); \
const android::String16& \
I##INTERFACE::getInterfaceDescriptor() const { \
return I##INTERFACE::descriptor; \
} \
android::sp<I##INTERFACE> I##INTERFACE::asInterface( \
const android::sp<android::IBinder>& obj) \
{ \
android::sp<I##INTERFACE> intr; \
if (obj != NULL) { \
intr = static_cast<I##INTERFACE*>( \
obj->queryLocalInterface( \
I##INTERFACE::descriptor).get()); \
if (intr == NULL) { \
intr = new Bp##INTERFACE(obj); \
} \
} \
return intr; \
} \
I##INTERFACE::I##INTERFACE() { } \
I##INTERFACE::~I##INTERFACE() { } \
#define CHECK_INTERFACE(interface, data, reply) \
if (!data.checkInterface(this)) { return PERMISSION_DENIED; } \
static const android::String16 descriptor; \
static android::sp<I##INTERFACE> asInterface( \
const android::sp<android::IBinder>& obj); \
virtual const android::String16& getInterfaceDescriptor() const; \
I##INTERFACE(); \
virtual ~I##INTERFACE(); \
#define IMPLEMENT_META_INTERFACE(INTERFACE, NAME) \
const android::String16 I##INTERFACE::descriptor(NAME); \
const android::String16& \
I##INTERFACE::getInterfaceDescriptor() const { \
return I##INTERFACE::descriptor; \
} \
android::sp<I##INTERFACE> I##INTERFACE::asInterface( \
const android::sp<android::IBinder>& obj) \
{ \
android::sp<I##INTERFACE> intr; \
if (obj != NULL) { \
intr = static_cast<I##INTERFACE*>( \
obj->queryLocalInterface( \
I##INTERFACE::descriptor).get()); \
if (intr == NULL) { \
intr = new Bp##INTERFACE(obj); \
} \
} \
return intr; \
} \
I##INTERFACE::I##INTERFACE() { } \
I##INTERFACE::~I##INTERFACE() { } \
#define CHECK_INTERFACE(interface, data, reply) \
if (!data.checkInterface(this)) { return PERMISSION_DENIED; } \