services/surfaceflinger/Scheduler/VSyncDispatchTimerQueue.cpp - android_frameworks_native - Gitiles

 /*
  * Copyright 2019 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #define ATRACE_TAG ATRACE_TAG_GRAPHICS
 #include <android-base/stringprintf.h>
 #include <utils/Trace.h>
 #include <vector>

 #include "TimeKeeper.h"
 #include "VSyncDispatchTimerQueue.h"
 #include "VSyncTracker.h"

 namespace android::scheduler {
 using base::StringAppendF;

 VSyncDispatch::~VSyncDispatch() = default;
 VSyncTracker::~VSyncTracker() = default;
 TimeKeeper::~TimeKeeper() = default;

 VSyncDispatchTimerQueueEntry::VSyncDispatchTimerQueueEntry(std::string const& name,
                                                            VSyncDispatch::Callback const& cb,
                                                            nsecs_t minVsyncDistance)
       : mName(name),
         mCallback(cb),
         mWorkDuration(0),
         mEarliestVsync(0),
         mMinVsyncDistance(minVsyncDistance) {}

 std::optional<nsecs_t> VSyncDispatchTimerQueueEntry::lastExecutedVsyncTarget() const {
     return mLastDispatchTime;
 }

 std::string_view VSyncDispatchTimerQueueEntry::name() const {
     return mName;
 }

 std::optional<nsecs_t> VSyncDispatchTimerQueueEntry::wakeupTime() const {
     if (!mArmedInfo) {
         return {};
     }
     return {mArmedInfo->mActualWakeupTime};
 }

 std::optional<nsecs_t> VSyncDispatchTimerQueueEntry::targetVsync() const {
     if (!mArmedInfo) {
         return {};
     }
     return {mArmedInfo->mActualVsyncTime};
 }

 ScheduleResult VSyncDispatchTimerQueueEntry::schedule(nsecs_t workDuration, nsecs_t earliestVsync,
                                                       VSyncTracker& tracker, nsecs_t now) {
     auto nextVsyncTime =
             tracker.nextAnticipatedVSyncTimeFrom(std::max(earliestVsync, now + workDuration));

     bool const wouldSkipAVsyncTarget =
             mArmedInfo && (nextVsyncTime > (mArmedInfo->mActualVsyncTime + mMinVsyncDistance));
     if (wouldSkipAVsyncTarget) {
         return ScheduleResult::Scheduled;
     }

     bool const alreadyDispatchedForVsync = mLastDispatchTime &&
             ((*mLastDispatchTime + mMinVsyncDistance) >= nextVsyncTime &&
              (*mLastDispatchTime - mMinVsyncDistance) <= nextVsyncTime);
     if (alreadyDispatchedForVsync) {
         nextVsyncTime =
                 tracker.nextAnticipatedVSyncTimeFrom(*mLastDispatchTime + mMinVsyncDistance);
     }

     auto const nextWakeupTime = nextVsyncTime - workDuration;
     mWorkDuration = workDuration;
     mEarliestVsync = earliestVsync;
     mArmedInfo = {nextWakeupTime, nextVsyncTime};
     return ScheduleResult::Scheduled;
 }

 void VSyncDispatchTimerQueueEntry::addPendingWorkloadUpdate(nsecs_t workDuration,
                                                             nsecs_t earliestVsync) {
     mWorkloadUpdateInfo = {.earliestVsync = earliestVsync, .duration = workDuration};
 }

 bool VSyncDispatchTimerQueueEntry::hasPendingWorkloadUpdate() const {
     return mWorkloadUpdateInfo.has_value();
 }

 void VSyncDispatchTimerQueueEntry::update(VSyncTracker& tracker, nsecs_t now) {
     if (!mArmedInfo && !mWorkloadUpdateInfo) {
         return;
     }

     if (mWorkloadUpdateInfo) {
         mEarliestVsync = mWorkloadUpdateInfo->earliestVsync;
         mWorkDuration = mWorkloadUpdateInfo->duration;
         mWorkloadUpdateInfo.reset();
     }

     auto const nextVsyncTime =
             tracker.nextAnticipatedVSyncTimeFrom(std::max(mEarliestVsync, now + mWorkDuration));
     mArmedInfo = {nextVsyncTime - mWorkDuration, nextVsyncTime};
 }

 void VSyncDispatchTimerQueueEntry::disarm() {
     mArmedInfo.reset();
 }

 nsecs_t VSyncDispatchTimerQueueEntry::executing() {
     mLastDispatchTime = mArmedInfo->mActualVsyncTime;
     disarm();
     return *mLastDispatchTime;
 }

 void VSyncDispatchTimerQueueEntry::callback(nsecs_t vsyncTimestamp, nsecs_t wakeupTimestamp) {
     {
         std::lock_guard<std::mutex> lk(mRunningMutex);
         mRunning = true;
     }

     mCallback(vsyncTimestamp, wakeupTimestamp);

     std::lock_guard<std::mutex> lk(mRunningMutex);
     mRunning = false;
     mCv.notify_all();
 }

 void VSyncDispatchTimerQueueEntry::ensureNotRunning() {
     std::unique_lock<std::mutex> lk(mRunningMutex);
     mCv.wait(lk, [this]() REQUIRES(mRunningMutex) { return !mRunning; });
 }

 void VSyncDispatchTimerQueueEntry::dump(std::string& result) const {
     std::lock_guard<std::mutex> lk(mRunningMutex);
     std::string armedInfo;
     if (mArmedInfo) {
         StringAppendF(&armedInfo, "[wake up in %.2fms for vsync %.2fms from now]",
                       (mArmedInfo->mActualWakeupTime - systemTime()) / 1e6f,
                       (mArmedInfo->mActualVsyncTime - systemTime()) / 1e6f);
     }

     StringAppendF(&result, "\t\t%s: %s %s\n", mName.c_str(),
                   mRunning ? "(in callback function)" : "", armedInfo.c_str());
     StringAppendF(&result, "\t\t\tmWorkDuration: %.2fms mEarliestVsync: %.2fms relative to now\n",
                   mWorkDuration / 1e6f, (mEarliestVsync - systemTime()) / 1e6f);

     if (mLastDispatchTime) {
         StringAppendF(&result, "\t\t\tmLastDispatchTime: %.2fms ago\n",
                       (systemTime() - *mLastDispatchTime) / 1e6f);
     } else {
         StringAppendF(&result, "\t\t\tmLastDispatchTime unknown\n");
     }
 }

 VSyncDispatchTimerQueue::VSyncDispatchTimerQueue(std::unique_ptr<TimeKeeper> tk,
                                                  VSyncTracker& tracker, nsecs_t timerSlack,
                                                  nsecs_t minVsyncDistance)
       : mTimeKeeper(std::move(tk)),
         mTracker(tracker),
         mTimerSlack(timerSlack),
         mMinVsyncDistance(minVsyncDistance) {}

 VSyncDispatchTimerQueue::~VSyncDispatchTimerQueue() {
     std::lock_guard<decltype(mMutex)> lk(mMutex);
     cancelTimer();
 }

 void VSyncDispatchTimerQueue::cancelTimer() {
     mIntendedWakeupTime = kInvalidTime;
     mTimeKeeper->alarmCancel();
 }

 void VSyncDispatchTimerQueue::setTimer(nsecs_t targetTime, nsecs_t now) {
     mIntendedWakeupTime = targetTime;
     mTimeKeeper->alarmIn(std::bind(&VSyncDispatchTimerQueue::timerCallback, this),
                          targetTime - now);
     mLastTimerSchedule = mTimeKeeper->now();
 }

 void VSyncDispatchTimerQueue::rearmTimer(nsecs_t now) {
     rearmTimerSkippingUpdateFor(now, mCallbacks.end());
 }

 void VSyncDispatchTimerQueue::TraceBuffer::note(std::string_view name, nsecs_t alarmIn,
                                                 nsecs_t vsFor) {
     if (ATRACE_ENABLED()) {
         snprintf(str_buffer.data(), str_buffer.size(), "%.4s%s%" PRId64 "%s%" PRId64,
                  name.substr(0, kMaxNamePrint).data(), kTraceNamePrefix, alarmIn,
                  kTraceNameSeparator, vsFor);
     }
     ATRACE_NAME(str_buffer.data());
 }

 void VSyncDispatchTimerQueue::rearmTimerSkippingUpdateFor(
         nsecs_t now, CallbackMap::iterator const& skipUpdateIt) {
     std::optional<nsecs_t> min;
     std::optional<nsecs_t> targetVsync;
     std::optional<std::string_view> nextWakeupName;
     for (auto it = mCallbacks.begin(); it != mCallbacks.end(); it++) {
         auto& callback = it->second;
         if (!callback->wakeupTime() && !callback->hasPendingWorkloadUpdate()) {
             continue;
         }

         if (it != skipUpdateIt) {
             callback->update(mTracker, now);
         }
         auto const wakeupTime = *callback->wakeupTime();
         if (!min || (min && *min > wakeupTime)) {
             nextWakeupName = callback->name();
             min = wakeupTime;
             targetVsync = callback->targetVsync();
         }
     }

     if (min && (min < mIntendedWakeupTime)) {
         if (targetVsync && nextWakeupName) {
             mTraceBuffer.note(*nextWakeupName, *min - now, *targetVsync - now);
         }
         setTimer(*min, now);
     } else {
         ATRACE_NAME("cancel timer");
         cancelTimer();
     }
 }

 void VSyncDispatchTimerQueue::timerCallback() {
     struct Invocation {
         std::shared_ptr<VSyncDispatchTimerQueueEntry> callback;
         nsecs_t vsyncTimestamp;
         nsecs_t wakeupTimestamp;
     };
     std::vector<Invocation> invocations;
     {
         std::lock_guard<decltype(mMutex)> lk(mMutex);
         mLastTimerCallback = mTimeKeeper->now();
         for (auto it = mCallbacks.begin(); it != mCallbacks.end(); it++) {
             auto& callback = it->second;
             auto const wakeupTime = callback->wakeupTime();
             if (!wakeupTime) {
                 continue;
             }

             if (*wakeupTime < mIntendedWakeupTime + mTimerSlack) {
                 callback->executing();
                 invocations.emplace_back(
                         Invocation{callback, *callback->lastExecutedVsyncTarget(), *wakeupTime});
             }
         }

         mIntendedWakeupTime = kInvalidTime;
         rearmTimer(mTimeKeeper->now());
     }

     for (auto const& invocation : invocations) {
         invocation.callback->callback(invocation.vsyncTimestamp, invocation.wakeupTimestamp);
     }
 }

 VSyncDispatchTimerQueue::CallbackToken VSyncDispatchTimerQueue::registerCallback(
         Callback const& callbackFn, std::string callbackName) {
     std::lock_guard<decltype(mMutex)> lk(mMutex);
     return CallbackToken{
             mCallbacks
                     .emplace(++mCallbackToken,
                              std::make_shared<VSyncDispatchTimerQueueEntry>(callbackName,
                                                                             callbackFn,
                                                                             mMinVsyncDistance))
                     .first->first};
 }

 void VSyncDispatchTimerQueue::unregisterCallback(CallbackToken token) {
     std::shared_ptr<VSyncDispatchTimerQueueEntry> entry = nullptr;
     {
         std::lock_guard<decltype(mMutex)> lk(mMutex);
         auto it = mCallbacks.find(token);
         if (it != mCallbacks.end()) {
             entry = it->second;
             mCallbacks.erase(it);
         }
     }

     if (entry) {
         entry->ensureNotRunning();
     }
 }

 ScheduleResult VSyncDispatchTimerQueue::schedule(CallbackToken token, nsecs_t workDuration,
                                                  nsecs_t earliestVsync) {
     auto result = ScheduleResult::Error;
     {
         std::lock_guard<decltype(mMutex)> lk(mMutex);

         auto it = mCallbacks.find(token);
         if (it == mCallbacks.end()) {
             return result;
         }
         auto& callback = it->second;
         auto const now = mTimeKeeper->now();

         /* If the timer thread will run soon, we'll apply this work update via the callback
          * timer recalculation to avoid cancelling a callback that is about to fire. */
         auto const rearmImminent = now > mIntendedWakeupTime;
         if (CC_UNLIKELY(rearmImminent)) {
             callback->addPendingWorkloadUpdate(workDuration, earliestVsync);
             return ScheduleResult::Scheduled;
         }

         result = callback->schedule(workDuration, earliestVsync, mTracker, now);
         if (result == ScheduleResult::CannotSchedule) {
             return result;
         }

         if (callback->wakeupTime() < mIntendedWakeupTime - mTimerSlack) {
             rearmTimerSkippingUpdateFor(now, it);
         }
     }

     return result;
 }

 CancelResult VSyncDispatchTimerQueue::cancel(CallbackToken token) {
     std::lock_guard<decltype(mMutex)> lk(mMutex);

     auto it = mCallbacks.find(token);
     if (it == mCallbacks.end()) {
         return CancelResult::Error;
     }
     auto& callback = it->second;

     auto const wakeupTime = callback->wakeupTime();
     if (wakeupTime) {
         callback->disarm();

         if (*wakeupTime == mIntendedWakeupTime) {
             mIntendedWakeupTime = kInvalidTime;
             rearmTimer(mTimeKeeper->now());
         }
         return CancelResult::Cancelled;
     }
     return CancelResult::TooLate;
 }

 void VSyncDispatchTimerQueue::dump(std::string& result) const {
     std::lock_guard<decltype(mMutex)> lk(mMutex);
     StringAppendF(&result, "\tTimer:\n");
     mTimeKeeper->dump(result);
     StringAppendF(&result, "\tmTimerSlack: %.2fms mMinVsyncDistance: %.2fms\n", mTimerSlack / 1e6f,
                   mMinVsyncDistance / 1e6f);
     StringAppendF(&result, "\tmIntendedWakeupTime: %.2fms from now\n",
                   (mIntendedWakeupTime - mTimeKeeper->now()) / 1e6f);
     StringAppendF(&result, "\tmLastTimerCallback: %.2fms ago mLastTimerSchedule: %.2fms ago\n",
                   (mTimeKeeper->now() - mLastTimerCallback) / 1e6f,
                   (mTimeKeeper->now() - mLastTimerSchedule) / 1e6f);
     StringAppendF(&result, "\tCallbacks:\n");
     for (const auto& [token, entry] : mCallbacks) {
         entry->dump(result);
     }
 }

 VSyncCallbackRegistration::VSyncCallbackRegistration(VSyncDispatch& dispatch,
                                                      VSyncDispatch::Callback const& callbackFn,
                                                      std::string const& callbackName)
       : mDispatch(dispatch),
         mToken(dispatch.registerCallback(callbackFn, callbackName)),
         mValidToken(true) {}

 VSyncCallbackRegistration::VSyncCallbackRegistration(VSyncCallbackRegistration&& other)
       : mDispatch(other.mDispatch),
         mToken(std::move(other.mToken)),
         mValidToken(std::move(other.mValidToken)) {
     other.mValidToken = false;
 }

 VSyncCallbackRegistration& VSyncCallbackRegistration::operator=(VSyncCallbackRegistration&& other) {
     mDispatch = std::move(other.mDispatch);
     mToken = std::move(other.mToken);
     mValidToken = std::move(other.mValidToken);
     other.mValidToken = false;
     return *this;
 }

 VSyncCallbackRegistration::~VSyncCallbackRegistration() {
     if (mValidToken) mDispatch.get().unregisterCallback(mToken);
 }

 ScheduleResult VSyncCallbackRegistration::schedule(nsecs_t workDuration, nsecs_t earliestVsync) {
     if (!mValidToken) {
         return ScheduleResult::Error;
     }
     return mDispatch.get().schedule(mToken, workDuration, earliestVsync);
 }

 CancelResult VSyncCallbackRegistration::cancel() {
     if (!mValidToken) {
         return CancelResult::Error;
     }
     return mDispatch.get().cancel(mToken);
 }

 } // namespace android::scheduler
	/*
	* Copyright 2019 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#define ATRACE_TAG ATRACE_TAG_GRAPHICS
	#include <android-base/stringprintf.h>
	#include <utils/Trace.h>
	#include <vector>

	#include "TimeKeeper.h"
	#include "VSyncDispatchTimerQueue.h"
	#include "VSyncTracker.h"

	namespace android::scheduler {
	using base::StringAppendF;

	VSyncDispatch::~VSyncDispatch() = default;
	VSyncTracker::~VSyncTracker() = default;
	TimeKeeper::~TimeKeeper() = default;

	VSyncDispatchTimerQueueEntry::VSyncDispatchTimerQueueEntry(std::string const& name,
	VSyncDispatch::Callback const& cb,
	nsecs_t minVsyncDistance)
	: mName(name),
	mCallback(cb),
	mWorkDuration(0),
	mEarliestVsync(0),
	mMinVsyncDistance(minVsyncDistance) {}

	std::optional<nsecs_t> VSyncDispatchTimerQueueEntry::lastExecutedVsyncTarget() const {
	return mLastDispatchTime;
	}

	std::string_view VSyncDispatchTimerQueueEntry::name() const {
	return mName;
	}

	std::optional<nsecs_t> VSyncDispatchTimerQueueEntry::wakeupTime() const {
	if (!mArmedInfo) {
	return {};
	}
	return {mArmedInfo->mActualWakeupTime};
	}

	std::optional<nsecs_t> VSyncDispatchTimerQueueEntry::targetVsync() const {
	if (!mArmedInfo) {
	return {};
	}
	return {mArmedInfo->mActualVsyncTime};
	}

	ScheduleResult VSyncDispatchTimerQueueEntry::schedule(nsecs_t workDuration, nsecs_t earliestVsync,
	VSyncTracker& tracker, nsecs_t now) {
	auto nextVsyncTime =
	tracker.nextAnticipatedVSyncTimeFrom(std::max(earliestVsync, now + workDuration));

	bool const wouldSkipAVsyncTarget =
	mArmedInfo && (nextVsyncTime > (mArmedInfo->mActualVsyncTime + mMinVsyncDistance));
	if (wouldSkipAVsyncTarget) {
	return ScheduleResult::Scheduled;
	}

	bool const alreadyDispatchedForVsync = mLastDispatchTime &&
	((*mLastDispatchTime + mMinVsyncDistance) >= nextVsyncTime &&
	(*mLastDispatchTime - mMinVsyncDistance) <= nextVsyncTime);
	if (alreadyDispatchedForVsync) {
	nextVsyncTime =
	tracker.nextAnticipatedVSyncTimeFrom(*mLastDispatchTime + mMinVsyncDistance);
	}

	auto const nextWakeupTime = nextVsyncTime - workDuration;
	mWorkDuration = workDuration;
	mEarliestVsync = earliestVsync;
	mArmedInfo = {nextWakeupTime, nextVsyncTime};
	return ScheduleResult::Scheduled;
	}

	void VSyncDispatchTimerQueueEntry::addPendingWorkloadUpdate(nsecs_t workDuration,
	nsecs_t earliestVsync) {
	mWorkloadUpdateInfo = {.earliestVsync = earliestVsync, .duration = workDuration};
	}

	bool VSyncDispatchTimerQueueEntry::hasPendingWorkloadUpdate() const {
	return mWorkloadUpdateInfo.has_value();
	}

	void VSyncDispatchTimerQueueEntry::update(VSyncTracker& tracker, nsecs_t now) {
	if (!mArmedInfo && !mWorkloadUpdateInfo) {
	return;
	}

	if (mWorkloadUpdateInfo) {
	mEarliestVsync = mWorkloadUpdateInfo->earliestVsync;
	mWorkDuration = mWorkloadUpdateInfo->duration;
	mWorkloadUpdateInfo.reset();
	}

	auto const nextVsyncTime =
	tracker.nextAnticipatedVSyncTimeFrom(std::max(mEarliestVsync, now + mWorkDuration));
	mArmedInfo = {nextVsyncTime - mWorkDuration, nextVsyncTime};
	}

	void VSyncDispatchTimerQueueEntry::disarm() {
	mArmedInfo.reset();
	}

	nsecs_t VSyncDispatchTimerQueueEntry::executing() {
	mLastDispatchTime = mArmedInfo->mActualVsyncTime;
	disarm();
	return *mLastDispatchTime;
	}

	void VSyncDispatchTimerQueueEntry::callback(nsecs_t vsyncTimestamp, nsecs_t wakeupTimestamp) {
	{
	std::lock_guard<std::mutex> lk(mRunningMutex);
	mRunning = true;
	}

	mCallback(vsyncTimestamp, wakeupTimestamp);

	std::lock_guard<std::mutex> lk(mRunningMutex);
	mRunning = false;
	mCv.notify_all();
	}

	void VSyncDispatchTimerQueueEntry::ensureNotRunning() {
	std::unique_lock<std::mutex> lk(mRunningMutex);
	mCv.wait(lk, [this]() REQUIRES(mRunningMutex) { return !mRunning; });
	}

	void VSyncDispatchTimerQueueEntry::dump(std::string& result) const {
	std::lock_guard<std::mutex> lk(mRunningMutex);
	std::string armedInfo;
	if (mArmedInfo) {
	StringAppendF(&armedInfo, "[wake up in %.2fms for vsync %.2fms from now]",
	(mArmedInfo->mActualWakeupTime - systemTime()) / 1e6f,
	(mArmedInfo->mActualVsyncTime - systemTime()) / 1e6f);
	}

	StringAppendF(&result, "\t\t%s: %s %s\n", mName.c_str(),
	mRunning ? "(in callback function)" : "", armedInfo.c_str());
	StringAppendF(&result, "\t\t\tmWorkDuration: %.2fms mEarliestVsync: %.2fms relative to now\n",
	mWorkDuration / 1e6f, (mEarliestVsync - systemTime()) / 1e6f);

	if (mLastDispatchTime) {
	StringAppendF(&result, "\t\t\tmLastDispatchTime: %.2fms ago\n",
	(systemTime() - *mLastDispatchTime) / 1e6f);
	} else {
	StringAppendF(&result, "\t\t\tmLastDispatchTime unknown\n");
	}
	}

	VSyncDispatchTimerQueue::VSyncDispatchTimerQueue(std::unique_ptr<TimeKeeper> tk,
	VSyncTracker& tracker, nsecs_t timerSlack,
	nsecs_t minVsyncDistance)
	: mTimeKeeper(std::move(tk)),
	mTracker(tracker),
	mTimerSlack(timerSlack),
	mMinVsyncDistance(minVsyncDistance) {}

	VSyncDispatchTimerQueue::~VSyncDispatchTimerQueue() {
	std::lock_guard<decltype(mMutex)> lk(mMutex);
	cancelTimer();
	}

	void VSyncDispatchTimerQueue::cancelTimer() {
	mIntendedWakeupTime = kInvalidTime;
	mTimeKeeper->alarmCancel();
	}

	void VSyncDispatchTimerQueue::setTimer(nsecs_t targetTime, nsecs_t now) {
	mIntendedWakeupTime = targetTime;
	mTimeKeeper->alarmIn(std::bind(&VSyncDispatchTimerQueue::timerCallback, this),
	targetTime - now);
	mLastTimerSchedule = mTimeKeeper->now();
	}

	void VSyncDispatchTimerQueue::rearmTimer(nsecs_t now) {
	rearmTimerSkippingUpdateFor(now, mCallbacks.end());
	}

	void VSyncDispatchTimerQueue::TraceBuffer::note(std::string_view name, nsecs_t alarmIn,
	nsecs_t vsFor) {
	if (ATRACE_ENABLED()) {
	snprintf(str_buffer.data(), str_buffer.size(), "%.4s%s%" PRId64 "%s%" PRId64,
	name.substr(0, kMaxNamePrint).data(), kTraceNamePrefix, alarmIn,
	kTraceNameSeparator, vsFor);
	}
	ATRACE_NAME(str_buffer.data());
	}

	void VSyncDispatchTimerQueue::rearmTimerSkippingUpdateFor(
	nsecs_t now, CallbackMap::iterator const& skipUpdateIt) {
	std::optional<nsecs_t> min;
	std::optional<nsecs_t> targetVsync;
	std::optional<std::string_view> nextWakeupName;
	for (auto it = mCallbacks.begin(); it != mCallbacks.end(); it++) {
	auto& callback = it->second;
	if (!callback->wakeupTime() && !callback->hasPendingWorkloadUpdate()) {
	continue;
	}

	if (it != skipUpdateIt) {
	callback->update(mTracker, now);
	}
	auto const wakeupTime = *callback->wakeupTime();
	if (!min \|\| (min && *min > wakeupTime)) {
	nextWakeupName = callback->name();
	min = wakeupTime;
	targetVsync = callback->targetVsync();
	}
	}

	if (min && (min < mIntendedWakeupTime)) {
	if (targetVsync && nextWakeupName) {
	mTraceBuffer.note(nextWakeupName, min - now, *targetVsync - now);
	}
	setTimer(*min, now);
	} else {
	ATRACE_NAME("cancel timer");
	cancelTimer();
	}
	}

	void VSyncDispatchTimerQueue::timerCallback() {
	struct Invocation {
	std::shared_ptr<VSyncDispatchTimerQueueEntry> callback;
	nsecs_t vsyncTimestamp;
	nsecs_t wakeupTimestamp;
	};
	std::vector<Invocation> invocations;
	{
	std::lock_guard<decltype(mMutex)> lk(mMutex);
	mLastTimerCallback = mTimeKeeper->now();
	for (auto it = mCallbacks.begin(); it != mCallbacks.end(); it++) {
	auto& callback = it->second;
	auto const wakeupTime = callback->wakeupTime();
	if (!wakeupTime) {
	continue;
	}

	if (*wakeupTime < mIntendedWakeupTime + mTimerSlack) {
	callback->executing();
	invocations.emplace_back(
	Invocation{callback, callback->lastExecutedVsyncTarget(), wakeupTime});
	}
	}

	mIntendedWakeupTime = kInvalidTime;
	rearmTimer(mTimeKeeper->now());
	}

	for (auto const& invocation : invocations) {
	invocation.callback->callback(invocation.vsyncTimestamp, invocation.wakeupTimestamp);
	}
	}

	VSyncDispatchTimerQueue::CallbackToken VSyncDispatchTimerQueue::registerCallback(
	Callback const& callbackFn, std::string callbackName) {
	std::lock_guard<decltype(mMutex)> lk(mMutex);
	return CallbackToken{
	mCallbacks
	.emplace(++mCallbackToken,
	std::make_shared<VSyncDispatchTimerQueueEntry>(callbackName,
	callbackFn,
	mMinVsyncDistance))
	.first->first};
	}

	void VSyncDispatchTimerQueue::unregisterCallback(CallbackToken token) {
	std::shared_ptr<VSyncDispatchTimerQueueEntry> entry = nullptr;
	{
	std::lock_guard<decltype(mMutex)> lk(mMutex);
	auto it = mCallbacks.find(token);
	if (it != mCallbacks.end()) {
	entry = it->second;
	mCallbacks.erase(it);
	}
	}

	if (entry) {
	entry->ensureNotRunning();
	}
	}

	ScheduleResult VSyncDispatchTimerQueue::schedule(CallbackToken token, nsecs_t workDuration,
	nsecs_t earliestVsync) {
	auto result = ScheduleResult::Error;
	{
	std::lock_guard<decltype(mMutex)> lk(mMutex);

	auto it = mCallbacks.find(token);
	if (it == mCallbacks.end()) {
	return result;
	}
	auto& callback = it->second;
	auto const now = mTimeKeeper->now();

	/* If the timer thread will run soon, we'll apply this work update via the callback
	* timer recalculation to avoid cancelling a callback that is about to fire. */
	auto const rearmImminent = now > mIntendedWakeupTime;
	if (CC_UNLIKELY(rearmImminent)) {
	callback->addPendingWorkloadUpdate(workDuration, earliestVsync);
	return ScheduleResult::Scheduled;
	}

	result = callback->schedule(workDuration, earliestVsync, mTracker, now);
	if (result == ScheduleResult::CannotSchedule) {
	return result;
	}

	if (callback->wakeupTime() < mIntendedWakeupTime - mTimerSlack) {
	rearmTimerSkippingUpdateFor(now, it);
	}
	}

	return result;
	}

	CancelResult VSyncDispatchTimerQueue::cancel(CallbackToken token) {
	std::lock_guard<decltype(mMutex)> lk(mMutex);

	auto it = mCallbacks.find(token);
	if (it == mCallbacks.end()) {
	return CancelResult::Error;
	}
	auto& callback = it->second;

	auto const wakeupTime = callback->wakeupTime();
	if (wakeupTime) {
	callback->disarm();

	if (*wakeupTime == mIntendedWakeupTime) {
	mIntendedWakeupTime = kInvalidTime;
	rearmTimer(mTimeKeeper->now());
	}
	return CancelResult::Cancelled;
	}
	return CancelResult::TooLate;
	}

	void VSyncDispatchTimerQueue::dump(std::string& result) const {
	std::lock_guard<decltype(mMutex)> lk(mMutex);
	StringAppendF(&result, "\tTimer:\n");
	mTimeKeeper->dump(result);
	StringAppendF(&result, "\tmTimerSlack: %.2fms mMinVsyncDistance: %.2fms\n", mTimerSlack / 1e6f,
	mMinVsyncDistance / 1e6f);
	StringAppendF(&result, "\tmIntendedWakeupTime: %.2fms from now\n",
	(mIntendedWakeupTime - mTimeKeeper->now()) / 1e6f);
	StringAppendF(&result, "\tmLastTimerCallback: %.2fms ago mLastTimerSchedule: %.2fms ago\n",
	(mTimeKeeper->now() - mLastTimerCallback) / 1e6f,
	(mTimeKeeper->now() - mLastTimerSchedule) / 1e6f);
	StringAppendF(&result, "\tCallbacks:\n");
	for (const auto& [token, entry] : mCallbacks) {
	entry->dump(result);
	}
	}

	VSyncCallbackRegistration::VSyncCallbackRegistration(VSyncDispatch& dispatch,
	VSyncDispatch::Callback const& callbackFn,
	std::string const& callbackName)
	: mDispatch(dispatch),
	mToken(dispatch.registerCallback(callbackFn, callbackName)),
	mValidToken(true) {}

	VSyncCallbackRegistration::VSyncCallbackRegistration(VSyncCallbackRegistration&& other)
	: mDispatch(other.mDispatch),
	mToken(std::move(other.mToken)),
	mValidToken(std::move(other.mValidToken)) {
	other.mValidToken = false;
	}

	VSyncCallbackRegistration& VSyncCallbackRegistration::operator=(VSyncCallbackRegistration&& other) {
	mDispatch = std::move(other.mDispatch);
	mToken = std::move(other.mToken);
	mValidToken = std::move(other.mValidToken);
	other.mValidToken = false;
	return *this;
	}

	VSyncCallbackRegistration::~VSyncCallbackRegistration() {
	if (mValidToken) mDispatch.get().unregisterCallback(mToken);
	}

	ScheduleResult VSyncCallbackRegistration::schedule(nsecs_t workDuration, nsecs_t earliestVsync) {
	if (!mValidToken) {
	return ScheduleResult::Error;
	}
	return mDispatch.get().schedule(mToken, workDuration, earliestVsync);
	}

	CancelResult VSyncCallbackRegistration::cancel() {
	if (!mValidToken) {
	return CancelResult::Error;
	}
	return mDispatch.get().cancel(mToken);
	}

	} // namespace android::scheduler