新进程如何启动binder线程监听binder请求

Zygote收到AMS创建新进程的请求后，会生成ZygoteConnection，然后调用runOnce

ZygoteConnection.runOnce

boolean runOnce() throws ZygoteInit.MethodAndArgsCaller {
       try {
            pid = Zygote.forkAndSpecialize(parsedArgs.uid, parsedArgs.gid, parsedArgs.gids,
                    parsedArgs.debugFlags, rlimits, parsedArgs.mountExternal, parsedArgs.seInfo,
                    parsedArgs.niceName, fdsToClose, parsedArgs.instructionSet,
                    parsedArgs.appDataDir);
        } catch (ErrnoException ex) {
            logAndPrintError(newStderr, "Exception creating pipe", ex);
        } catch (IllegalArgumentException ex) {
            logAndPrintError(newStderr, "Invalid zygote arguments", ex);
        } catch (ZygoteSecurityException ex) {
            logAndPrintError(newStderr,
                    "Zygote security policy prevents request: ", ex);
        }

        try {
            if (pid == 0) {
                .....
                handleChildProc(parsedArgs, descriptors, childPipeFd, newStderr);

                // should never get here, the child is expected to either
                // throw ZygoteInit.MethodAndArgsCaller or exec().
                return true;
            }
    }

ZygoteConnection.handleChildProc

    private void handleChildProc(Arguments parsedArgs,
            FileDescriptor[] descriptors, FileDescriptor pipeFd, PrintStream newStderr)
            throws ZygoteInit.MethodAndArgsCaller {
        
        if (parsedArgs.invokeWith != null) {
            ......
        } else {
            RuntimeInit.zygoteInit(parsedArgs.targetSdkVersion,
                    parsedArgs.remainingArgs, null /* classLoader */);
        }
    }

Runtime.zygoteInit

public static final void zygoteInit(int targetSdkVersion, String[] argv, ClassLoader classLoader)
        throws ZygoteInit.MethodAndArgsCaller {
    .....
    commonInit();
    nativeZygoteInit();
    applicationInit(targetSdkVersion, argv, classLoader);
}

static void com_android_internal_os_RuntimeInit_nativeZygoteInit(JNIEnv* env, jobject clazz)
{
    gCurRuntime->onZygoteInit();
}

class AppRuntime : public AndroidRuntime
{
    virtual void onZygoteInit()
    {
        sp proc = ProcessState::self();
        ALOGV("App process: starting thread pool.\n");
        proc->startThreadPool();
    }

void ProcessState::startThreadPool()
{
    AutoMutex _l(mLock);
    if (!mThreadPoolStarted) {
        mThreadPoolStarted = true;
        spawnPooledThread(true);
    }
}

void ProcessState::spawnPooledThread(bool isMain)
{
    if (mThreadPoolStarted) {
        String8 name = makeBinderThreadName();
        ALOGV("Spawning new pooled thread, name=%s\n", name.string());
        sp t = new PoolThread(isMain);
        t->run(name.string());
    }
}

最后创建一个PoolThread然后监听binder请求。

PoolThread定义：

class PoolThread : public Thread
{
public:
    PoolThread(bool isMain)
        : mIsMain(isMain)
    {
    }
    
protected:
    virtual bool threadLoop()
    {
        IPCThreadState::self()->joinThreadPool(mIsMain);
        return false;
    }
    
    const bool mIsMain;
};

void IPCThreadState::joinThreadPool(bool isMain)
{
    .....
        
    status_t result;
    do {
        // now get the next command to be processed, waiting if necessary
        result = getAndExecuteCommand();

    } while (result != -ECONNREFUSED && result != -EBADF);

}