android核心机制之Zygote启动流程

Zygote实际上是一个进程繁殖器,通过socket的select模型进行繁殖.类似命令的方式来进行Fork.
下面绘制了其流程图.

可以看到:

1.Zygote服务实际上是一种Select服务模型.
2.为了启动java代码,进行了一次androidRuntime的打开和关闭.
3.启动的SystemServer进程,此进程启动了一个线程注册了很多服务之后,开启了手机的HOME(也就是桌面),然后开始服务循环.(注意:此服务是Binder服务,Binder服务一启动就是俩线程。可能是因为是两个CPU吧。
代码如下：
4.Zygote进入select循环系统,开始服务.
5.此服务是很简单的，而且是通用的服务代码。（也就是取数据，传输数据，与SOCKET有些类似）。上层必须基于此服务原型来写相应的代码。

Java代码
ProcessState::self()->startThreadPool();//启动一个。
IPCThreadState::self()->joinThreadPool();//把此线程也加入。

Cpp代码
case BR_TRANSACTION:
    {
        binder_transaction_data tr;
        result = mIn.read(&tr, sizeof(tr));
        LOG_ASSERT(result == NO_ERROR,
            "Not enough command data for brTRANSACTION");
        if (result != NO_ERROR) break;

        Parcel buffer;
        buffer.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);

        const pid_t origPid = mCallingPid;
        const uid_t origUid = mCallingUid;

        mCallingPid = tr.sender_pid;
        mCallingUid = tr.sender_euid;

        int curPrio = getpriority(PRIO_PROCESS, mMyThreadId);
        if (gDisableBackgroundScheduling) {
            if (curPrio > ANDROID_PRIORITY_NORMAL) {
                // We have inherited a reduced priority from the caller, but do not
                // want to run in that state in this process. The driver set our
                // priority already (though not our scheduling class), so bounce
                // it back to the default before invoking the transaction.
                setpriority(PRIO_PROCESS, mMyThreadId, ANDROID_PRIORITY_NORMAL);
            }
        } else {
            if (curPrio >= ANDROID_PRIORITY_BACKGROUND) {
                // We want to use the inherited priority from the caller.
                // Ensure this thread is in the background scheduling class,
                // since the driver won't modify scheduling classes for us.
                // The scheduling group is reset to default by the caller
                // once this method returns after the transaction is complete.
                androidSetThreadSchedulingGroup(mMyThreadId,
                                                ANDROID_TGROUP_BG_NONINTERACT);
            }
        }

        //LOGI(">>>> TRANSACT from pid %d uid %d\n", mCallingPid, mCallingUid);

        Parcel reply;
        IF_LOG_TRANSACTIONS() {
            TextOutput::Bundle _b(alog);
            alog << "BR_TRANSACTION thr " << (void*)pthread_self()
                << " / obj " << tr.target.ptr << " / code "
                << TypeCode(tr.code) << ": " << indent << buffer
                << dedent << endl
                << "Data addr = "
                << reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer)
                << ", offsets addr="
                << reinterpret_cast<const size_t*>(tr.data.ptr.offsets) << endl;
        }
        if (tr.target.ptr) {
            sp<BBinder> b((BBinder*)tr.cookie);
            const status_t error = b->transact(tr.code, buffer, &reply, 0);
            if (error < NO_ERROR) reply.setError(error);

补充：移动开发 , Android ,