android核心机制之Zygote启动流程

1.先说一下android中的服务，一种是系统服务，系统服务通过getSystemService方法获得,所有的系统服务运行在一个进程中.

 

2.还有一种是自定义Service,也就是通过startService启动. 这种服务是单独一个进程.

 

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:

启动完ServiceManager后，启动Zygote和SystemServer进程。

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。

 

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

 

    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);
                
            } else {
                const status_t error = the_context_object->transact(tr.code, buffer, &reply, 0);
                if (error < NO_ERROR) reply.setError(error);
            }
            
            //LOGI("<<<< TRANSACT from pid %d restore pid %d uid %d\n",
            //     mCallingPid, origPid, origUid);
            
            if ((tr.flags & TF_ONE_WAY) == 0) {
                LOG_ONEWAY("Sending reply to %d!", mCallingPid);
                sendReply(reply, 0);
            } else {
                LOG_ONEWAY("NOT sending reply to %d!", mCallingPid);
            }
            
            mCallingPid = origPid;
            mCallingUid = origUid;

            IF_LOG_TRANSACTIONS() {
                TextOutput::Bundle _b(alog);
                alog << "BC_REPLY thr " << (void*)pthread_self() << " / obj "
                    << tr.target.ptr << ": " << indent << reply << dedent << endl;
            }
            
        }
        break;