SurfaceFlinger

WMS在添加窗口后需要向SurfaceFlinger申请Surface。首先WMS需要先获得SurfaceFlinger的代理。在WindowState对象创建后利用win.attach()为APP申请建立SurfaceFlinger的链接。

void attach() {
    if (WindowManagerService.localLOGV) Slog.v(
    mSession.windowAddedLocked();
}

void windowAddedLocked() {
    if (mSurfaceSession == null) {
       // SurfaceSession新建
        mSurfaceSession = new SurfaceSession();
        mService.mSessions.add(this);
       ...
    }
    mNumWindow++;
}

SurfaceSession持有SurfaceFlinger的代理SurfaceComposerClient，如下：

    public SurfaceSession() {
        mNativeClient = nativeCreate();
    }

    static jlong nativeCreate(JNIEnv* env, jclass clazz) {
        SurfaceComposerClient* client = new SurfaceComposerClient();
        client->incStrong((void*)nativeCreate);
        return reinterpret_cast<jlong>(client);
    }

Session与APP进程一一对应，它会进一步为当前进程建立SurfaceSession会话。

Session是APP同WMS通信的通道，SurfaceSession是WMS为APP向SurfaceFlinger申请的通信通道，同样 SurfaceSession与APP也是一一对应的，既然是同SurfaceFlinger通信的信使，那么SurfaceSession就应该握着SurfaceFlinger的代理，其实就是SurfaceComposerClient里的ISurfaceComposerClient mClient对象，它是SurfaceFlinger为每个APP封装一个代理，也就是 **进程 <-> Session <-> SurfaceSession <-> SurfaceComposerClient <-> ISurfaceComposerClient(BpSurfaceComposerClient) **五者是一条线。