// This will return when (1) a vsync event has been received, and (2) there was
// at least one connection interested in receiving it when we started waiting.
Vector< sp<EventThread::Connection> > EventThread::waitForEvent(
DisplayEventReceiver::Event* event)
{
Mutex::Autolock _l(mLock);
Vector< sp<EventThread::Connection> > signalConnections;
do {
bool eventPending = false;
bool waitForVSync = false;
size_t vsyncCount = 0;
nsecs_t timestamp = 0;
for (int32_t i=0 ; i<DisplayDevice::NUM_BUILTIN_DISPLAY_TYPES ; i++) {
timestamp = mVSyncEvent[i].header.timestamp;
if (timestamp) {
// we have a vsync event to dispatch
*event = mVSyncEvent[i];
mVSyncEvent[i].header.timestamp = 0;
vsyncCount = mVSyncEvent[i].vsync.count;
break;
}
}
if (!timestamp) {
// no vsync event, see if there are some other event
eventPending = !mPendingEvents.isEmpty();
if (eventPending) {
// we have some other event to dispatch
*event = mPendingEvents[0];
mPendingEvents.removeAt(0);
}
}
// find out connections waiting for events
size_t count = mDisplayEventConnections.size();
for (size_t i=0 ; i<count ; i++) {
sp<Connection> connection(mDisplayEventConnections[i].promote());
if (connection != NULL) {
bool added = false;
if (connection->count >= 0) {
// we need vsync events because at least
// one connection is waiting for it
waitForVSync = true;
if (timestamp) {
// we consume the event only if it's time
// (ie: we received a vsync event)
if (connection->count == 0) {
// fired this time around
connection->count = -1;
signalConnections.add(connection);
added = true;
} else if (connection->count == 1 ||
(vsyncCount % connection->count) == 0) {
// continuous event, and time to report it
signalConnections.add(connection);
added = true;
}
}
}
if (eventPending && !timestamp && !added) {
// we don't have a vsync event to process
// (timestamp==0), but we have some pending
// messages.
signalConnections.add(connection);
}
} else {
// we couldn't promote this reference, the connection has
// died, so clean-up!
mDisplayEventConnections.removeAt(i);
--i; --count;
}
}
// Here we figure out if we need to enable or disable vsyncs
if (timestamp && !waitForVSync) {
// we received a VSYNC but we have no clients
// don't report it, and disable VSYNC events
disableVSyncLocked();
} else if (!timestamp && waitForVSync) {
// we have at least one client, so we want vsync enabled
// (TODO: this function is called right after we finish
// notifying clients of a vsync, so this call will be made
// at the vsync rate, e.g. 60fps. If we can accurately
// track the current state we could avoid making this call
// so often.)
enableVSyncLocked();
}
// note: !timestamp implies signalConnections.isEmpty(), because we
// don't populate signalConnections if there's no vsync pending
if (!timestamp && !eventPending) {
// wait for something to happen
if (waitForVSync) {
// This is where we spend most of our time, waiting
// for vsync events and new client registrations.
//
// If the screen is off, we can't use h/w vsync, so we
// use a 16ms timeout instead. It doesn't need to be
// precise, we just need to keep feeding our clients.
//
// We don't want to stall if there's a driver bug, so we
// use a (long) timeout when waiting for h/w vsync, and
// generate fake events when necessary.
bool softwareSync = mUseSoftwareVSync;
nsecs_t timeout = softwareSync ? ms2ns(16) : ms2ns(1000);
if (mCondition.waitRelative(mLock, timeout) == TIMED_OUT) {
if (!softwareSync) {
ALOGW("Timed out waiting for hw vsync; faking it");
}
// FIXME: how do we decide which display id the fake
// vsync came from ?
mVSyncEvent[0].header.type = DisplayEventReceiver::DISPLAY_EVENT_VSYNC;
mVSyncEvent[0].header.id = DisplayDevice::DISPLAY_PRIMARY;
mVSyncEvent[0].header.timestamp = systemTime(SYSTEM_TIME_MONOTONIC);
mVSyncEvent[0].vsync.count++;
}
} else {
// Nobody is interested in vsync, so we just want to sleep.
// h/w vsync should be disabled, so this will wait until we
// get a new connection, or an existing connection becomes
// interested in receiving vsync again.
mCondition.wait(mLock);
}
}
} while (signalConnections.isEmpty());
// here we're guaranteed to have a timestamp and some connections to signal
// (The connections might have dropped out of mDisplayEventConnections
// while we were asleep, but we'll still have strong references to them.)
return signalConnections;
}
// This will return when (1) a vsync event has been received, and (2) there was
// at least one connection interested in receiving it when we started waiting.
Vector< sp<EventThread::Connection> > EventThread::waitForEvent(
DisplayEventReceiver::Event* event) // 这个东西会block住
{
Mutex::Autolock _l(mLock);
Vector< sp<EventThread::Connection> > signalConnections;
do {
bool eventPending = false;
bool waitForVSync = false;
size_t vsyncCount = 0; // 回来的VSYNC有多少
nsecs_t timestamp = 0;
for (int32_t i = 0; i < HWC_DISPLAY_TYPES_SUPPORTED; i++) {
timestamp = mVSyncEvent[i].header.timestamp; // timestamp会被新的事件的timestamp给覆盖掉
if (timestamp) {
// we have a vsync event to dispatch
*event = mVSyncEvent[i];
mVSyncEvent[i].header.timestamp = 0;
vsyncCount = mVSyncEvent[i].vsync.count;
break;
}
}
if (!timestamp) {
// no vsync event, see if there are some other event
eventPending = !mPendingEvents.isEmpty(); // 目前这里主要就是HOT-PLUG事件
if (eventPending) {
// we have some other event to dispatch
*event = mPendingEvents[0]; // Good, we got one finally
mPendingEvents.removeAt(0);
}
}
// find out connections waiting for events
size_t count = mDisplayEventConnections.size(); // 多个请求display事件的连接
for (size_t i = 0; i < count; i++) {
sp<Connection> connection(mDisplayEventConnections[i].promote());
if (connection != NULL) {
bool added = false;
if (connection->count >= 0) {
// we need vsync events because at least
// one connection is waiting for it
waitForVSync = true;
if (timestamp) {
// we consume the event only if it's time
// (ie: we received a vsync event)
if (connection->count == 0) {
// fired this time around
connection->count = -1;
signalConnections.add(connection);
added = true;
} else if (connection->count == 1 ||
(vsyncCount % connection->count) == 0) { // 这个vsyncCount什么意义？ connection->count可能很大吗？
// 0 / 5
// 这是相对于已有的VSYNC比较的，比如每间隔5个VSYNC返回一个
// 给客户端， 1就是每个都返回
// continuous event, and time to report it
signalConnections.add(connection);
added = true;
}
}
} // 针对-1的情况，都不触发，如果变成0了，肯定是有人执行了requestNextVsync
if (eventPending && !timestamp && !added) { // 没有VSYNC，但是有其他事件
// we don't have a vsync event to process
// (timestamp == 0), but we have some pending
// messages.
signalConnections.add(connection);
}
} else {
// we couldn't promote this reference, the connection has
// died, so clean-up!
mDisplayEventConnections.removeAt(i);
--i; --count; // Good
}
}
// Here we figure out if we need to enable or disable vsyncs
if (timestamp && !waitForVSync) { // Cool，没有人请求就不用report，但是目前看来至少有一个吧，就是我们SurfaceFlinger用的
// we received a VSYNC but we have no clients
// don't report it, and disable VSYNC events
disableVSyncLocked();
} else if (!timestamp && waitForVSync) {
// we have at least one client, so we want vsync enabled
// (TODO: this function is called right after we finish
// notifying clients of a vsync, so this call will be made
// at the vsync rate, e.g. 60fps. If we can accurately
// track the current state we could avoid making this call
// so often.)
enableVSyncLocked(); // 这个是同步的吗？
}
// note: !timestamp implies signalConnections.isEmpty(), because we
// don't populate signalConnections if there's no vsync pending
if (!timestamp && !eventPending) {
// wait for something to happen
if (waitForVSync) {
// This is where we spend most of our time, waiting
// for vsync events and new client registrations.
//
// If the screen is off, we can't use h/w vsync, so we
// use a 16ms timeout instead. It doesn't need to be
// precise, we just need to keep feeding our clients.
//
// We don't want to stall if there's a driver bug, so we
// use a (long) timeout when waiting for h/w vsync, and
// generate fake events when necessary.
bool softwareSync = mUseSoftwareVSync;
nsecs_t timeout = softwareSync ? ms2ns(16) : ms2ns(1000); // 如果DRV有bug，我们还是可以继续进行，只是时间不准
if (mCondition.waitRelative(mLock, timeout) == TIMED_OUT) {
if (!softwareSync) {
ALOGW("Timed out waiting for hw vsync; faking it");
}
// FIXME: how do we decide which display id the fake
// vsync came from ?
// 好问题
mVSyncEvent[0].header.type = DisplayEventReceiver::DISPLAY_EVENT_VSYNC;
mVSyncEvent[0].header.id = HWC_DISPLAY_PRIMARY;
mVSyncEvent[0].header.timestamp = systemTime(SYSTEM_TIME_MONOTONIC);
mVSyncEvent[0].vsync.count++;
}
} else {
// Nobody is interested in vsync, so we just want to sleep.
// h/w vsync should be disabled, so this will wait until we
// get a new connection, or an existing connection becomes
// interested in receiving vsync again.
mCondition.wait(mLock); // 没有人对VSYNC感兴趣，所以我们需要关闭硬件VSYNC，然后在此睡眠
}
}
} while (signalConnections.isEmpty());
// here we're guaranteed to have a timestamp and some connections to signal
// (The connections might have dropped out of mDisplayEventConnections
// while we were asleep, but we'll still have strong references to them.)
return signalConnections;
}
