在viewrootimpl中进行的初始化。
初始化的时候进行了framehandler，framedisplayeventreceiver的初始化。
framedisplayeventreceiver实现了DisplayEventReceiver,初始化的时候进行了nativeinit，进入到jni层。
在DisplayEventReceiver进行nativeinit的时候，需要创建nativeDisplayeventreceiver,并且进行initialize。
nativeDisplayeventreceiver继承自Displayeventdispatcher，然后调用initialize。
在Displayeventdispatcher的initialize中，DisplayEventReceiver调用initcheck
49status_t DisplayEventReceiver::initCheck() const {
50 if (mDataChannel != NULL)
51 return NO_ERROR;
52 return NO_INIT;
53}
监听获取到的receiver文件句柄。
于是在收到底层的vsync信号的时候，就会回调Displayeventdispatcher的handleevent函数
89int DisplayEventDispatcher::handleEvent(int, int events, void*) {
...
102 // Drain all pending events, keep the last vsync.
103 nsecs_t vsyncTimestamp;
104 int32_t vsyncDisplayId;
105 uint32_t vsyncCount;
106 if (processPendingEvents(&vsyncTimestamp, &vsyncDisplayId, &vsyncCount)) {
107 ALOGV("dispatcher %p ~ Vsync pulse: timestamp=%" PRId64 ", id=%d, count=%d",
108 this, ns2ms(vsyncTimestamp), vsyncDisplayId, vsyncCount);
109 mWaitingForVsync = false;
110 dispatchVsync(vsyncTimestamp, vsyncDisplayId, vsyncCount);
111 }
112
113 return 1; // keep the callback
114}
调用了自身的processpendingevent，又分成热插拔和vsync
116bool DisplayEventDispatcher::processPendingEvents(
117 nsecs_t* outTimestamp, int32_t* outId, uint32_t* outCount) {
118 bool gotVsync = false;
...
126 case DisplayEventReceiver::DISPLAY_EVENT_VSYNC:
127 // Later vsync events will just overwrite the info from earlier
128 // ones. That's fine, we only care about the most recent.
129 gotVsync = true;//进入vsync
130 *outTimestamp = ev.header.timestamp;
131 *outId = ev.header.id;
132 *outCount = ev.vsync.count;
133 break;
134 case DisplayEventReceiver::DISPLAY_EVENT_HOTPLUG:
135 dispatchHotplug(ev.header.timestamp, ev.header.id, ev.hotplug.connected);
136 break;
...
146 return gotVsync;
147}
然后就回到了android_view_displayeventreceiver.cpp中，进行vsync的dispatch
87void NativeDisplayEventReceiver::dispatchVsync(nsecs_t timestamp, int32_t id, uint32_t count) {
90 ScopedLocalRef<jobject> receiverObj(env, jniGetReferent(env, mReceiverWeakGlobal));
91 if (receiverObj.get()) {
92 ALOGV("receiver %p ~ Invoking vsync handler.", this);
93 env->CallVoidMethod(receiverObj.get(),
94 gDisplayEventReceiverClassInfo.dispatchVsync, timestamp, id, count);
95 ALOGV("receiver %p ~ Returned from vsync handler.", this);
96 }
97
98 mMessageQueue->raiseAndClearException(env, "dispatchVsync");
99}
获取到当时传下来的FrameDisplayEventReceiver，回调他的父类的dispatchvsync，也就是他自己的onvsync
942 public void onVsync(long timestampNanos, int builtInDisplayId, int frame) {
982 Message msg = Message.obtain(mHandler, this);
983 msg.setAsynchronous(true);
984 mHandler.sendMessageAtTime(msg, timestampNanos / TimeUtils.NANOS_PER_MS);
985 }
传入的是自己runnable，所以调用了自己的run方法，于是调用了doframe
685 void doFrame(long frameTimeNanos, int frame) {
744 mFrameInfo.markInputHandlingStart();
745 doCallbacks(Choreographer.CALLBACK_INPUT, frameTimeNanos);
746
747 mFrameInfo.markAnimationsStart();
748 doCallbacks(Choreographer.CALLBACK_ANIMATION, frameTimeNanos);
749
750 mFrameInfo.markPerformTraversalsStart();
751 doCallbacks(Choreographer.CALLBACK_TRAVERSAL, frameTimeNanos);
752
753 doCallbacks(Choreographer.CALLBACK_COMMIT, frameTimeNanos);
765 }
调用了docallback
767 void doCallbacks(int callbackType, long frameTimeNanos) {
810 for (CallbackRecord c = callbacks; c != null; c = c.next) {
811 if (DEBUG_FRAMES) {
812 Log.d(TAG, "RunCallback: type=" + callbackType
813 + ", action=" + c.action + ", token=" + c.token
814 + ", latencyMillis=" + (SystemClock.uptimeMillis() - c.dueTime));
815 }
816 c.run(frameTimeNanos);
817 }
829 }
取出对应的回调，调用其中的方法。