Choreographer启动流程
在Activity启动过程，执行完onResume后，会调用Activity.makeVisible()，然后再调用到addView()， 层层调用会进入如下方法：
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public ViewRootImpl(Context context, Display display) {
...
//获取Choreographer实例
mChoreographer = Choreographer.getInstance();
...
}
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getInstance()
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//frameworks/base/core/java/android/view/Choreographer.java
public static Choreographer getInstance() {
return sThreadInstance.get();
}
// Thread local storage for the choreographer.
private static final ThreadLocal<Choreographer> sThreadInstance =
new ThreadLocal<Choreographer>() {
@Override
protected Choreographer initialValue() {
//获取当前线程Looper
Looper looper = Looper.myLooper();
if (looper == null) {
throw new IllegalStateException("The current thread must have a looper!");
}
Choreographer choreographer = new Choreographer(looper, VSYNC_SOURCE_APP);
if (looper == Looper.getMainLooper()) {
mMainInstance = choreographer;
}
return choreographer;
}
};
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创建Choreographer
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//frameworks/base/core/java/android/view/Choreographer.java
private Choreographer(Looper looper, int vsyncSource) {
mLooper = looper;
//创建Handler
mHandler = new FrameHandler(looper);
//创建用于接收Vsync的对象
mDisplayEventReceiver = USE_VSYNC
? new FrameDisplayEventReceiver(looper, vsyncSource)
: null;
//上一次帧绘制时间点
mLastFrameTimeNanos = Long.MIN_VALUE;
//帧间时长
mFrameIntervalNanos = (long)(1000000000 / getRefreshRate());
//创建回调对象
mCallbackQueues = new CallbackQueue[CALLBACK_LAST + 1];
for (int i = 0; i <= CALLBACK_LAST; i++) {
mCallbackQueues[i] = new CallbackQueue();
}
// b/68769804: For low FPS experiments.
setFPSDivisor(SystemProperties.getInt(ThreadedRenderer.DEBUG_FPS_DIVISOR, 1));
}
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创建FrameHandler
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private final class FrameHandler extends Handler {
public FrameHandler(Looper looper) {
super(looper);
}
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case MSG_DO_FRAME:
doFrame(System.nanoTime(), 0);
break;
case MSG_DO_SCHEDULE_VSYNC:
doScheduleVsync();
break;
case MSG_DO_SCHEDULE_CALLBACK:
doScheduleCallback(msg.arg1);
break;
}
}
}
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postCallback
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public void postCallback(int callbackType, Runnable action, Object token) {
postCallbackDelayed(callbackType, action, token, 0);
}
public void postCallbackDelayed(int callbackType,
Runnable action, Object token, long delayMillis) {
if (action == null) {
throw new IllegalArgumentException("action must not be null");
}
if (callbackType < 0 || callbackType > CALLBACK_LAST) {
throw new IllegalArgumentException("callbackType is invalid");
}
postCallbackDelayedInternal(callbackType, action, token, delayMillis);
}
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postCallbackDelayedInternal
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private void postCallbackDelayedInternal(int callbackType,
Object action, Object token, long delayMillis) {
if (DEBUG_FRAMES) {
Log.d(TAG, "PostCallback: type=" + callbackType
+ ", action=" + action + ", token=" + token
+ ", delayMillis=" + delayMillis);
}
synchronized (mLock) {
final long now = SystemClock.uptimeMillis();
final long dueTime = now + delayMillis;
// 1. 将 mTraversalRunnable 塞入队列
mCallbackQueues[callbackType].addCallbackLocked(dueTime, action, token);
if (dueTime <= now) {// 立即执行
// 2. 由于 delayMillis 是 0，所以会执行到这里
scheduleFrameLocked(now);
} else {// 延迟执行
Message msg = mHandler.obtainMessage(MSG_DO_SCHEDULE_CALLBACK, action);
msg.arg1 = callbackType;
msg.setAsynchronous(true);
mHandler.sendMessageAtTime(msg, dueTime);
}
}
}
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private void scheduleFrameLocked(long now) {
if (!mFrameScheduled) {
mFrameScheduled = true;
if (USE_VSYNC) {
// Android 4.1 之后 USE_VSYNCUSE_VSYNC 默认为 true
if (DEBUG_FRAMES) {
Log.d(TAG, "Scheduling next frame on vsync.");
}
// If running on the Looper thread, then schedule the vsync immediately,
// otherwise post a message to schedule the vsync from the UI thread
// as soon as possible.
//如果是当前线程，直接申请 vsync，否则通过 handler 通信
if (isRunningOnLooperThreadLocked()) {
scheduleVsyncLocked();
} else {
Message msg = mHandler.obtainMessage(MSG_DO_SCHEDULE_VSYNC);
msg.setAsynchronous(true);
mHandler.sendMessageAtFrontOfQueue(msg);
}
} else {
final long nextFrameTime = Math.max(
mLastFrameTimeNanos / TimeUtils.NANOS_PER_MS + sFrameDelay, now);
if (DEBUG_FRAMES) {
Log.d(TAG, "Scheduling next frame in " + (nextFrameTime - now) + " ms.");
}
Message msg = mHandler.obtainMessage(MSG_DO_FRAME);
msg.setAsynchronous(true);
mHandler.sendMessageAtTime(msg, nextFrameTime);
}
}
}
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private void scheduleVsyncLocked() {
mDisplayEventReceiver.scheduleVsync();
}
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@UnsupportedAppUsage
public void scheduleVsync() {
if (mReceiverPtr == 0) {
Log.w(TAG, "Attempted to schedule a vertical sync pulse but the display event "
+ "receiver has already been disposed.");
} else {
// 注册监听 vsync 信号，会回调 dispatchVsync() 方法
nativeScheduleVsync(mReceiverPtr);
}
}
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创建FrameDisplayEventReceiver
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private final class FrameDisplayEventReceiver extends DisplayEventReceiver
implements Runnable {
private boolean mHavePendingVsync;
private long mTimestampNanos;
private int mFrame;
public FrameDisplayEventReceiver(Looper looper, int vsyncSource) {
super(looper, vsyncSource, CONFIG_CHANGED_EVENT_SUPPRESS);
}
}
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DisplayEventReceiver
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@UnsupportedAppUsage
public DisplayEventReceiver(Looper looper) {
this(looper, VSYNC_SOURCE_APP, CONFIG_CHANGED_EVENT_SUPPRESS);
}
public DisplayEventReceiver(Looper looper, int vsyncSource, int configChanged) {
if (looper == null) {
throw new IllegalArgumentException("looper must not be null");
}
//获取主线程消息队列
mMessageQueue = looper.getQueue();
//调用Native方法
mReceiverPtr = nativeInit(new WeakReference<DisplayEventReceiver>(this), mMessageQueue,
vsyncSource, configChanged);
mCloseGuard.open("dispose");
}
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nativeInit
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//android_view_DisplayEventReceiver.cpp
static jlong nativeInit(JNIEnv* env, jclass clazz, jobject receiverWeak,
jobject messageQueueObj, jint vsyncSource, jint configChanged) {
//获取MessageQueue
sp<MessageQueue> messageQueue = android_os_MessageQueue_getMessageQueue(env, messageQueueObj);
if (messageQueue == NULL) {
jniThrowRuntimeException(env, "MessageQueue is not initialized.");
return 0;
}
//创建NativeDisplayEventReceiver对象
sp<NativeDisplayEventReceiver> receiver = new NativeDisplayEventReceiver(env,
receiverWeak, messageQueue, vsyncSource, configChanged);
status_t status = receiver->initialize();
if (status) {
String8 message;
message.appendFormat("Failed to initialize display event receiver. status=%d", status);
jniThrowRuntimeException(env, message.string());
return 0;
}
//获取DisplayEventReceiver对象的引用
receiver->incStrong(gDisplayEventReceiverClassInfo.clazz); // retain a reference for the object
return reinterpret_cast<jlong>(receiver.get());
}
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创建NativeDisplayEventReceiver
NativeDisplayEventReceiver继承于LooperCallback对象，此处mReceiverWeakGlobal记录的是Java层 DisplayEventReceiver对象的全局引用。
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//可以看做是构造函数调用父类的构造函数
NativeDisplayEventReceiver::NativeDisplayEventReceiver(JNIEnv* env,
jobject receiverWeak, const sp<MessageQueue>& messageQueue, jint vsyncSource,
jint configChanged) :
DisplayEventDispatcher(messageQueue->getLooper(),//获取Looper
static_cast<ISurfaceComposer::VsyncSource>(vsyncSource),
static_cast<ISurfaceComposer::ConfigChanged>(configChanged)),
mReceiverWeakGlobal(env->NewGlobalRef(receiverWeak)),
mMessageQueue(messageQueue) {
ALOGV("receiver %p ~ Initializing display event receiver.", this);
}
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initialize
DisplayEventDispatcher继承LooperCallback
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//androidfw/DisplayEventDispatcher.h
class DisplayEventDispatcher : public LooperCallback
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//androidfw/DisplayEventDispatcher.cpp
status_t DisplayEventDispatcher::initialize() {
//mReceiver为DisplayEventReceiver类型
status_t result = mReceiver.initCheck();
if (result) {
ALOGW("Failed to initialize display event receiver, status=%d", result);
return result;
}
//监听mReceiver的所获取的文件句柄
int rc = mLooper->addFd(mReceiver.getFd(), 0, Looper::EVENT_INPUT,
this, NULL);
if (rc < 0) {
return UNKNOWN_ERROR;
}
return OK;
}
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监听mReceiver的所获取的文件句柄，一旦有数据到来，则回调this(此处NativeDisplayEventReceiver)中所复写LooperCallback对象的 handleEvent。
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//Looper.cpp
int Looper::addFd(int fd, int ident, int events, Looper_callbackFunc callback, void* data) {
return addFd(fd, ident, events, callback ? new SimpleLooperCallback(callback) : nullptr, data);
}
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Vysnc回调流程
handleEvent
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//androidfw/DisplayEventDispatcher.cpp
int DisplayEventDispatcher::handleEvent(int, int events, void*) {
if (events & (Looper::EVENT_ERROR | Looper::EVENT_HANGUP)) {
ALOGE("Display event receiver pipe was closed or an error occurred. "
"events=0x%x", events);
return 0; // remove the callback
}
if (!(events & Looper::EVENT_INPUT)) {
ALOGW("Received spurious callback for unhandled poll event. "
"events=0x%x", events);
return 1; // keep the callback
}
// Drain all pending events, keep the last vsync.
nsecs_t vsyncTimestamp;
PhysicalDisplayId vsyncDisplayId;
uint32_t vsyncCount;
//清除所有的pending事件，只保留最后一次vsync
if (processPendingEvents(&vsyncTimestamp, &vsyncDisplayId, &vsyncCount)) {
ALOGV("dispatcher %p ~ Vsync pulse: timestamp=%" PRId64 ", displayId=%"
ANDROID_PHYSICAL_DISPLAY_ID_FORMAT ", count=%d",
this, ns2ms(vsyncTimestamp), vsyncDisplayId, vsyncCount);
mWaitingForVsync = false;
//分发Vsync
dispatchVsync(vsyncTimestamp, vsyncDisplayId, vsyncCount);
}
return 1; // keep the callback
}
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processPendingEvents
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bool NativeDisplayEventReceiver::processPendingEvents(
nsecs_t* outTimestamp, int32_t* outId, uint32_t* outCount) {
bool gotVsync = false;
DisplayEventReceiver::Event buf[EVENT_BUFFER_SIZE];
ssize_t n;
while ((n = mReceiver.getEvents(buf, EVENT_BUFFER_SIZE)) > 0) {
for (ssize_t i = 0; i < n; i++) {
const DisplayEventReceiver::Event& ev = buf[i];
switch (ev.header.type) {
case DisplayEventReceiver::DISPLAY_EVENT_VSYNC:
gotVsync = true; //获取VSync信号
*outTimestamp = ev.header.timestamp;
*outId = ev.header.id;
*outCount = ev.vsync.count;
break;
case DisplayEventReceiver::DISPLAY_EVENT_HOTPLUG:
dispatchHotplug(ev.header.timestamp, ev.header.id, ev.hotplug.connected);
break;
default:
break;
}
}
}
return gotVsync;
}
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遍历所有的事件，当有多个VSync事件到来，则只关注最近一次的事件。
dispatchVsync
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void NativeDisplayEventReceiver::dispatchVsync(nsecs_t timestamp, PhysicalDisplayId displayId,
uint32_t count) {
JNIEnv* env = AndroidRuntime::getJNIEnv();
ScopedLocalRef<jobject> receiverObj(env, jniGetReferent(env, mReceiverWeakGlobal));
if (receiverObj.get()) {
ALOGV("receiver %p ~ Invoking vsync handler.", this);
env->CallVoidMethod(receiverObj.get(),
gDisplayEventReceiverClassInfo.dispatchVsync, timestamp, displayId, count);
ALOGV("receiver %p ~ Returned from vsync handler.", this);
}
mMessageQueue->raiseAndClearException(env, "dispatchVsync");
}
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此处调用到Java层的DisplayEventReceiver对象的dispatchVsync()方法，接下来进入Java层。
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//DisplayEventReceiver.java
private void dispatchVsync(long timestampNanos, long physicalDisplayId, int frame) {
onVsync(timestampNanos, physicalDisplayId, frame);
}
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Choreographer对象实例化的过程，创建的对象是DisplayEventReceiver子类 FrameDisplayEventReceiver对象，接下来进入该对象。
onVsync
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//FrameDisplayEventReceiver.java
@Override
public void onVsync(long timestampNanos, long physicalDisplayId, int frame) {
// Post the vsync event to the Handler.
// The idea is to prevent incoming vsync events from completely starving
// the message queue. If there are no messages in the queue with timestamps
// earlier than the frame time, then the vsync event will be processed immediately.
// Otherwise, messages that predate the vsync event will be handled first.
long now = System.nanoTime();
if (timestampNanos > now) {
Log.w(TAG, "Frame time is " + ((timestampNanos - now) * 0.000001f)
+ " ms in the future! Check that graphics HAL is generating vsync "
+ "timestamps using the correct timebase.");
timestampNanos = now;
}
if (mHavePendingVsync) {
Log.w(TAG, "Already have a pending vsync event. There should only be "
+ "one at a time.");
} else {
mHavePendingVsync = true;
}
mTimestampNanos = timestampNanos;
mFrame = frame;
Message msg = Message.obtain(mHandler, this);
msg.setAsynchronous(true);
mHandler.sendMessageAtTime(msg, timestampNanos / TimeUtils.NANOS_PER_MS);
}
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可见onVsync()过程是通过FrameHandler向主线程Looper发送了一个自带callback的消息，此处callback为FrameDisplayEventReceiver。 当主线程Looper执行到该消息时，则调用FrameDisplayEventReceiver.run()方法.
run()
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@Override
public void run() {
mHavePendingVsync = false;
doFrame(mTimestampNanos, mFrame);
}
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doFrame()
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@UnsupportedAppUsage
void doFrame(long frameTimeNanos, int frame) {
final long startNanos;
synchronized (mLock) {
//false直接返回
if (!mFrameScheduled) {
return; // no work to do
}
if (DEBUG_JANK && mDebugPrintNextFrameTimeDelta) {
mDebugPrintNextFrameTimeDelta = false;
Log.d(TAG, "Frame time delta: "
+ ((frameTimeNanos - mLastFrameTimeNanos) * 0.000001f) + " ms");
}
long intendedFrameTimeNanos = frameTimeNanos;
startNanos = System.nanoTime();
final long jitterNanos = startNanos - frameTimeNanos;
if (jitterNanos >= mFrameIntervalNanos) {
final long skippedFrames = jitterNanos / mFrameIntervalNanos;
//当掉帧个数超过30，则输出响应log
if (skippedFrames >= SKIPPED_FRAME_WARNING_LIMIT) {
Log.i(TAG, "Skipped " + skippedFrames + " frames! "
+ "The application may be doing too much work on its main thread.");
}
final long lastFrameOffset = jitterNanos % mFrameIntervalNanos;
if (DEBUG_JANK) {
Log.d(TAG, "Missed vsync by " + (jitterNanos * 0.000001f) + " ms "
+ "which is more than the frame interval of "
+ (mFrameIntervalNanos * 0.000001f) + " ms! "
+ "Skipping " + skippedFrames + " frames and setting frame "
+ "time to " + (lastFrameOffset * 0.000001f) + " ms in the past.");
}
frameTimeNanos = startNanos - lastFrameOffset;
}
if (frameTimeNanos < mLastFrameTimeNanos) {
if (DEBUG_JANK) {
Log.d(TAG, "Frame time appears to be going backwards. May be due to a "
+ "previously skipped frame. Waiting for next vsync.");
}
scheduleVsyncLocked();
return;
}
if (mFPSDivisor > 1) {
long timeSinceVsync = frameTimeNanos - mLastFrameTimeNanos;
if (timeSinceVsync < (mFrameIntervalNanos * mFPSDivisor) && timeSinceVsync > 0) {
scheduleVsyncLocked();
return;
}
}
mFrameInfo.setVsync(intendedFrameTimeNanos, frameTimeNanos);
mFrameScheduled = false;
mLastFrameTimeNanos = frameTimeNanos;
}
try {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "Choreographer#doFrame");
AnimationUtils.lockAnimationClock(frameTimeNanos / TimeUtils.NANOS_PER_MS);
mFrameInfo.markInputHandlingStart();
doCallbacks(Choreographer.CALLBACK_INPUT, frameTimeNanos);
//标记动画开始时间
mFrameInfo.markAnimationsStart();
//执行回调方法
doCallbacks(Choreographer.CALLBACK_ANIMATION, frameTimeNanos);
doCallbacks(Choreographer.CALLBACK_INSETS_ANIMATION, frameTimeNanos);
mFrameInfo.markPerformTraversalsStart();
doCallbacks(Choreographer.CALLBACK_TRAVERSAL, frameTimeNanos);
doCallbacks(Choreographer.CALLBACK_COMMIT, frameTimeNanos);
} finally {
AnimationUtils.unlockAnimationClock();
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
if (DEBUG_FRAMES) {
final long endNanos = System.nanoTime();
Log.d(TAG, "Frame " + frame + ": Finished, took "
+ (endNanos - startNanos) * 0.000001f + " ms, latency "
+ (startNanos - frameTimeNanos) * 0.000001f + " ms.");
}
}
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此处frameTimeNanos是底层VSYNC信号到达的时间戳。
- 每调用一次scheduleFrameLocked()，则mFrameScheduled=true，能执行一次doFrame()操作，执行完doFrame()并设置mFrameScheduled=false；
- 最终有4个回调类别，如下所示：
- INPUT：输入事件
- ANIMATION：动画
- TRAVERSAL：窗口刷新，执行measure/layout/draw操作
- COMMIT：遍历完成的提交操作，用来修正动画启动时间
doCallbacks
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void doCallbacks(int callbackType, long frameTimeNanos) {
CallbackRecord callbacks;
synchronized (mLock) {
// We use "now" to determine when callbacks become due because it's possible
// for earlier processing phases in a frame to post callbacks that should run
// in a following phase, such as an input event that causes an animation to start.
final long now = System.nanoTime();
//从队列查找相应类型的CallbackRecord对象
callbacks = mCallbackQueues[callbackType].extractDueCallbacksLocked(
now / TimeUtils.NANOS_PER_MS);
if (callbacks == null) {
return;
}
mCallbacksRunning = true;
// Update the frame time if necessary when committing the frame.
// We only update the frame time if we are more than 2 frames late reaching
// the commit phase. This ensures that the frame time which is observed by the
// callbacks will always increase from one frame to the next and never repeat.
// We never want the next frame's starting frame time to end up being less than
// or equal to the previous frame's commit frame time. Keep in mind that the
// next frame has most likely already been scheduled by now so we play it
// safe by ensuring the commit time is always at least one frame behind.
if (callbackType == Choreographer.CALLBACK_COMMIT) {
final long jitterNanos = now - frameTimeNanos;
Trace.traceCounter(Trace.TRACE_TAG_VIEW, "jitterNanos", (int) jitterNanos);
//当commit类型回调执行的时间点超过2帧，则更新mLastFrameTimeNanos。
if (jitterNanos >= 2 * mFrameIntervalNanos) {
final long lastFrameOffset = jitterNanos % mFrameIntervalNanos
+ mFrameIntervalNanos;
if (DEBUG_JANK) {
Log.d(TAG, "Commit callback delayed by " + (jitterNanos * 0.000001f)
+ " ms which is more than twice the frame interval of "
+ (mFrameIntervalNanos * 0.000001f) + " ms! "
+ "Setting frame time to " + (lastFrameOffset * 0.000001f)
+ " ms in the past.");
mDebugPrintNextFrameTimeDelta = true;
}
frameTimeNanos = now - lastFrameOffset;
mLastFrameTimeNanos = frameTimeNanos;
}
}
}
try {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, CALLBACK_TRACE_TITLES[callbackType]);
for (CallbackRecord c = callbacks; c != null; c = c.next) {
if (DEBUG_FRAMES) {
Log.d(TAG, "RunCallback: type=" + callbackType
+ ", action=" + c.action + ", token=" + c.token
+ ", latencyMillis=" + (SystemClock.uptimeMillis() - c.dueTime));
}
c.run(frameTimeNanos);
}
} finally {
synchronized (mLock) {
mCallbacksRunning = false;
//回收callbacks，加入对象池mCallbackPool
do {
final CallbackRecord next = callbacks.next;
recycleCallbackLocked(callbacks);
callbacks = next;
} while (callbacks != null);
}
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
}
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该方法主要功能：
- 从队列头mHead查找CallbackRecord对象，当队列头部的callbacks对象为空或者执行时间还没到达，则直接返回；
- 开始执行相应回调的run()方法；
- 回收callbacks，加入对象池mCallbackPool，就是说callback一旦执行完成，则会被回收。
CallbackRecord
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private static final class CallbackRecord {
public CallbackRecord next;
public long dueTime;
public Object action; // Runnable or FrameCallback
public Object token;
@UnsupportedAppUsage
public void run(long frameTimeNanos) {
if (token == FRAME_CALLBACK_TOKEN) {
((FrameCallback)action).doFrame(frameTimeNanos);
} else {
((Runnable)action).run();
}
}
}
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这里的回调方法run()有两种执行情况：
- 当token的数据类型为FRAME_CALLBACK_TOKEN，则执行该对象的doFrame()方法;
- 当token为其他类型，则执行该对象的run()方法。
那么需要的场景便是由WMS调用scheduleAnimationLocked()方法来设置mFrameScheduled=true来触发动画， 接下来说说动画控制的过程。
动画显示过程
参考