media/utils/TimerThread.cpp - third_party/android/platform/frameworks/av - Git at Google

 /*
  * Copyright (C) 2021 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 LOG_TAG "TimerThread"

 #include <optional>
 #include <sstream>
 #include <unistd.h>
 #include <vector>

 #include <mediautils/MediaUtilsDelayed.h>
 #include <mediautils/TidWrapper.h>
 #include <mediautils/TimerThread.h>
 #include <utils/Log.h>
 #include <utils/ThreadDefs.h>

 using namespace std::chrono_literals;

 namespace android::mediautils {

 extern std::string formatTime(std::chrono::system_clock::time_point t);
 extern std::string_view timeSuffix(std::string_view time1, std::string_view time2);

 TimerThread::Handle TimerThread::scheduleTask(
         std::string_view tag, TimerCallback&& func,
         Duration timeoutDuration, Duration secondChanceDuration) {
     const auto now = std::chrono::system_clock::now();
     auto request = std::make_shared<const Request>(now, now +
             std::chrono::duration_cast<std::chrono::system_clock::duration>(timeoutDuration),
             secondChanceDuration, getThreadIdWrapper(), tag);
     return mMonitorThread.add(std::move(request), std::move(func), timeoutDuration);
 }

 TimerThread::Handle TimerThread::trackTask(std::string_view tag) {
     const auto now = std::chrono::system_clock::now();
     auto request = std::make_shared<const Request>(now, now,
             Duration{} /* secondChanceDuration */, getThreadIdWrapper(), tag);
     return mNoTimeoutMap.add(std::move(request));
 }

 bool TimerThread::cancelTask(Handle handle) {
     std::shared_ptr<const Request> request = isNoTimeoutHandle(handle) ?
              mNoTimeoutMap.remove(handle) : mMonitorThread.remove(handle);
     if (!request) return false;
     mRetiredQueue.add(std::move(request));
     return true;
 }


 std::string TimerThread::SnapshotAnalysis::toString() const {
     // Note: These request queues are snapshot very close together but
     // not at "identical" times as we don't use a class-wide lock.
     std::string analysisSummary = std::string("\nanalysis [ ").append(description).append(" ]");
     std::string timeoutStack;
     std::string blockedStack;
     if (timeoutTid != -1) {
         timeoutStack = std::string(suspectTid == timeoutTid ? "\ntimeout/blocked(" : "\ntimeout(")
                 .append(std::to_string(timeoutTid)).append(") callstack [\n")
                 .append(getCallStackStringForTid(timeoutTid)).append("]");
     }

     if (suspectTid != -1 && suspectTid != timeoutTid) {
         blockedStack = std::string("\nblocked(")
                 .append(std::to_string(suspectTid)).append(")  callstack [\n")
                 .append(getCallStackStringForTid(suspectTid)).append("]");
     }

     return std::string("now ")
             .append(formatTime(std::chrono::system_clock::now()))
             .append("\nsecondChanceCount ")
             .append(std::to_string(secondChanceCount))
             .append(analysisSummary)
             .append("\ntimeout [ ")
             .append(requestsToString(timeoutRequests))
             .append(" ]\npending [ ")
             .append(requestsToString(pendingRequests))
             .append(" ]\nretired [ ")
             .append(requestsToString(retiredRequests))
             .append(" ]")
             .append(timeoutStack)
             .append(blockedStack);
 }

 // A HAL method is where the substring "Hidl" is in the class name.
 // The tag should look like: ... Hidl ... :: ...
 // When the audio HAL is updated to AIDL perhaps we will use instead
 // a global directory of HAL classes.
 //
 // See MethodStatistics.cpp:
 // mediautils::getStatisticsClassesForModule(METHOD_STATISTICS_MODULE_NAME_AUDIO_HIDL)
 //
 /* static */
 bool TimerThread::isRequestFromHal(const std::shared_ptr<const Request>& request) {
     const size_t hidlPos = request->tag.asStringView().find("Hidl");
     if (hidlPos == std::string::npos) return false;
     // should be a separator afterwards Hidl which indicates the string was in the class.
     const size_t separatorPos = request->tag.asStringView().find("::", hidlPos);
     return separatorPos != std::string::npos;
 }

 struct TimerThread::SnapshotAnalysis TimerThread::getSnapshotAnalysis(size_t retiredCount) const {
     struct SnapshotAnalysis analysis{};
     // The following snapshot of the TimerThread state will be utilized for
     // analysis. Note, there is no lock around these calls, so there could be
     // a state update between them.
     mTimeoutQueue.copyRequests(analysis.timeoutRequests);
     mRetiredQueue.copyRequests(analysis.retiredRequests, retiredCount);
     analysis.pendingRequests = getPendingRequests();
     analysis.secondChanceCount = mMonitorThread.getSecondChanceCount();
     // No call has timed out, so there is no analysis to be done.
     if (analysis.timeoutRequests.empty())
         return analysis;
     // for now look at last timeout (in our case, the only timeout)
     const std::shared_ptr<const Request> timeout = analysis.timeoutRequests.back();
     analysis.timeoutTid = timeout->tid;
     if (analysis.pendingRequests.empty())
       return analysis;
     // pending Requests that are problematic.
     std::vector<std::shared_ptr<const Request>> pendingExact;
     std::vector<std::shared_ptr<const Request>> pendingPossible;

     // We look at pending requests that were scheduled no later than kPendingDuration
     // after the timeout request. This prevents false matches with calls
     // that naturally block for a short period of time
     // such as HAL write() and read().
     //
     constexpr Duration kPendingDuration = 1000ms;
     for (const auto& pending : analysis.pendingRequests) {
         // If the pending tid is the same as timeout tid, problem identified.
         if (pending->tid == timeout->tid) {
             pendingExact.emplace_back(pending);
             continue;
         }

         // if the pending tid is scheduled within time limit
         if (pending->scheduled - timeout->scheduled < kPendingDuration) {
             pendingPossible.emplace_back(pending);
         }
     }

     std::string& description = analysis.description;
     if (!pendingExact.empty()) {
         const auto& request = pendingExact.front();
         const bool hal = isRequestFromHal(request);

         if (hal) {
             description = std::string("Blocked directly due to HAL call: ")
                 .append(request->toString());
             analysis.suspectTid= request->tid;
         }
     }
     if (description.empty() && !pendingPossible.empty()) {
         for (const auto& request : pendingPossible) {
             const bool hal = isRequestFromHal(request);
             if (hal) {
                 // The first blocked call is the most likely one.
                 // Recent calls might be temporarily blocked
                 // calls such as write() or read() depending on kDuration.
                 description = std::string("Blocked possibly due to HAL call: ")
                     .append(request->toString());
                 analysis.suspectTid= request->tid;
             }
        }
     }
     return analysis;
 }

 std::vector<std::shared_ptr<const TimerThread::Request>> TimerThread::getPendingRequests() const {
     constexpr size_t kEstimatedPendingRequests = 8;  // approx 128 byte alloc.
     std::vector<std::shared_ptr<const Request>> pendingRequests;
     pendingRequests.reserve(kEstimatedPendingRequests); // preallocate vector out of lock.

     // following are internally locked calls, which add to our local pendingRequests.
     mMonitorThread.copyRequests(pendingRequests);
     mNoTimeoutMap.copyRequests(pendingRequests);

     // Sort in order of scheduled time.
     std::sort(pendingRequests.begin(), pendingRequests.end(),
         [](const std::shared_ptr<const Request>& r1,
            const std::shared_ptr<const Request>& r2) {
                return r1->scheduled < r2->scheduled;
            });
     return pendingRequests;
 }

 std::string TimerThread::pendingToString() const {
     return requestsToString(getPendingRequests());
 }

 std::string TimerThread::retiredToString(size_t n) const {
     std::vector<std::shared_ptr<const Request>> retiredRequests;
     mRetiredQueue.copyRequests(retiredRequests, n);

     // Dump to string
     return requestsToString(retiredRequests);
 }

 std::string TimerThread::timeoutToString(size_t n) const {
     std::vector<std::shared_ptr<const Request>> timeoutRequests;
     mTimeoutQueue.copyRequests(timeoutRequests, n);

     // Dump to string
     return requestsToString(timeoutRequests);
 }

 std::string TimerThread::Request::toString() const {
     const auto scheduledString = formatTime(scheduled);
     const auto deadlineString = formatTime(deadline);
     return std::string(tag)
         .append(" scheduled ").append(scheduledString)
         .append(" deadline ").append(timeSuffix(scheduledString, deadlineString))
         .append(" tid ").append(std::to_string(tid));
 }

 void TimerThread::RequestQueue::add(std::shared_ptr<const Request> request) {
     std::lock_guard lg(mRQMutex);
     mRequestQueue.emplace_back(std::chrono::system_clock::now(), std::move(request));
     if (mRequestQueue.size() > mRequestQueueMax) {
         mRequestQueue.pop_front();
     }
 }

 void TimerThread::RequestQueue::copyRequests(
         std::vector<std::shared_ptr<const Request>>& requests, size_t n) const {
     std::lock_guard lg(mRQMutex);
     const size_t size = mRequestQueue.size();
     size_t i = n >=  size ? 0 : size - n;
     for (; i < size; ++i) {
         const auto &[time, request] = mRequestQueue[i];
         requests.emplace_back(request);
     }
 }

 TimerThread::Handle TimerThread::NoTimeoutMap::add(std::shared_ptr<const Request> request) {
     std::lock_guard lg(mNTMutex);
     // A unique handle is obtained by mNoTimeoutRequests.fetch_add(1),
     // This need not be under a lock, but we do so anyhow.
     const Handle handle = getUniqueHandle_l();
     mMap[handle] = request;
     return handle;
 }

 std::shared_ptr<const TimerThread::Request> TimerThread::NoTimeoutMap::remove(Handle handle) {
     std::lock_guard lg(mNTMutex);
     auto it = mMap.find(handle);
     if (it == mMap.end()) return {};
     auto request = it->second;
     mMap.erase(it);
     return request;
 }

 void TimerThread::NoTimeoutMap::copyRequests(
         std::vector<std::shared_ptr<const Request>>& requests) const {
     std::lock_guard lg(mNTMutex);
     for (const auto &[handle, request] : mMap) {
         requests.emplace_back(request);
     }
 }

 TimerThread::MonitorThread::MonitorThread(RequestQueue& timeoutQueue)
         : mTimeoutQueue(timeoutQueue)
         , mThread([this] { threadFunc(); }) {
      pthread_setname_np(mThread.native_handle(), "TimerThread");
      pthread_setschedprio(mThread.native_handle(), PRIORITY_URGENT_AUDIO);
 }

 TimerThread::MonitorThread::~MonitorThread() {
     {
         std::lock_guard _l(mMutex);
         mShouldExit = true;
         mCond.notify_all();
     }
     mThread.join();
 }

 void TimerThread::MonitorThread::threadFunc() {
     std::unique_lock _l(mMutex);
     ::android::base::ScopedLockAssertion lock_assertion(mMutex);
     while (!mShouldExit) {
         Handle nextDeadline = INVALID_HANDLE;
         Handle now = INVALID_HANDLE;
         if (!mMonitorRequests.empty()) {
             nextDeadline = mMonitorRequests.begin()->first;
             now = std::chrono::steady_clock::now();
             if (nextDeadline < now) {
                 auto node = mMonitorRequests.extract(mMonitorRequests.begin());
                 // Deadline has expired, handle the request.
                 auto secondChanceDuration = node.mapped().first->secondChanceDuration;
                 if (secondChanceDuration.count() != 0) {
                     // We now apply the second chance duration to find the clock
                     // monotonic second deadline.  The unique key is then the
                     // pair<second_deadline, first_deadline>.
                     //
                     // The second chance prevents a false timeout should there be
                     // any clock monotonic advancement during suspend.
                     auto newHandle = now + secondChanceDuration;
                     ALOGD("%s: TimeCheck second chance applied for %s",
                             __func__, node.mapped().first->tag.c_str()); // should be rare event.
                     mSecondChanceRequests.emplace_hint(mSecondChanceRequests.end(),
                             std::make_pair(newHandle, nextDeadline),
                             std::move(node.mapped()));
                     // increment second chance counter.
                     mSecondChanceCount.fetch_add(1 /* arg */, std::memory_order_relaxed);
                 } else {
                     {
                         _l.unlock();
                         // We add Request to retired queue early so that it can be dumped out.
                         mTimeoutQueue.add(std::move(node.mapped().first));
                         node.mapped().second(nextDeadline);
                         // Caution: we don't hold lock when we call TimerCallback,
                         // but this is the timeout case!  We will crash soon,
                         // maybe before returning.
                         // anything left over is released here outside lock.
                     }
                     // reacquire the lock - if something was added, we loop immediately to check.
                     _l.lock();
                 }
                 // always process expiring monitor requests first.
                 continue;
             }
         }
         // now process any second chance requests.
         if (!mSecondChanceRequests.empty()) {
             Handle secondDeadline = mSecondChanceRequests.begin()->first.first;
             if (now == INVALID_HANDLE) now = std::chrono::steady_clock::now();
             if (secondDeadline < now) {
                 auto node = mSecondChanceRequests.extract(mSecondChanceRequests.begin());
                 {
                     _l.unlock();
                     // We add Request to retired queue early so that it can be dumped out.
                     mTimeoutQueue.add(std::move(node.mapped().first));
                     const Handle originalHandle = node.key().second;
                     node.mapped().second(originalHandle);
                     // Caution: we don't hold lock when we call TimerCallback.
                     // This is benign issue - we permit concurrent operations
                     // while in the callback to the MonitorQueue.
                     //
                     // Anything left over is released here outside lock.
                 }
                 // reacquire the lock - if something was added, we loop immediately to check.
                 _l.lock();
                 continue;
             }
             // update the deadline.
             if (nextDeadline == INVALID_HANDLE) {
                 nextDeadline = secondDeadline;
             } else {
                 nextDeadline = std::min(nextDeadline, secondDeadline);
             }
         }
         if (nextDeadline != INVALID_HANDLE) {
             mCond.wait_until(_l, nextDeadline);
         } else {
             mCond.wait(_l);
         }
     }
 }

 TimerThread::Handle TimerThread::MonitorThread::add(
         std::shared_ptr<const Request> request, TimerCallback&& func, Duration timeout) {
     std::lock_guard _l(mMutex);
     const Handle handle = getUniqueHandle_l(timeout);
     mMonitorRequests.emplace_hint(mMonitorRequests.end(),
             handle, std::make_pair(std::move(request), std::move(func)));
     mCond.notify_all();
     return handle;
 }

 std::shared_ptr<const TimerThread::Request> TimerThread::MonitorThread::remove(Handle handle) {
     std::pair<std::shared_ptr<const Request>, TimerCallback> data;
     std::unique_lock ul(mMutex);
     ::android::base::ScopedLockAssertion lock_assertion(mMutex);
     if (const auto it = mMonitorRequests.find(handle);
         it != mMonitorRequests.end()) {
         data = std::move(it->second);
         mMonitorRequests.erase(it);
         ul.unlock();  // manually release lock here so func (data.second)
                       // is released outside of lock.
         return data.first;  // request
     }

     // this check is O(N), but since the second chance requests are ordered
     // in terms of earliest expiration time, we would expect better than average results.
     for (auto it = mSecondChanceRequests.begin(); it != mSecondChanceRequests.end(); ++it) {
         if (it->first.second == handle) {
             data = std::move(it->second);
             mSecondChanceRequests.erase(it);
             ul.unlock();  // manually release lock here so func (data.second)
                           // is released outside of lock.
             return data.first; // request
         }
     }
     return {};
 }

 void TimerThread::MonitorThread::copyRequests(
         std::vector<std::shared_ptr<const Request>>& requests) const {
     std::lock_guard lg(mMutex);
     for (const auto &[deadline, monitorpair] : mMonitorRequests) {
         requests.emplace_back(monitorpair.first);
     }
     // we combine the second map with the first map - this is
     // everything that is pending on the monitor thread.
     // The second map will be older than the first map so this
     // is in order.
     for (const auto &[deadline, monitorpair] : mSecondChanceRequests) {
         requests.emplace_back(monitorpair.first);
     }
 }

 }  // namespace android::mediautils
	/*
	* Copyright (C) 2021 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 LOG_TAG "TimerThread"

	#include <optional>
	#include <sstream>
	#include <unistd.h>
	#include <vector>

	#include <mediautils/MediaUtilsDelayed.h>
	#include <mediautils/TidWrapper.h>
	#include <mediautils/TimerThread.h>
	#include <utils/Log.h>
	#include <utils/ThreadDefs.h>

	using namespace std::chrono_literals;

	namespace android::mediautils {

	extern std::string formatTime(std::chrono::system_clock::time_point t);
	extern std::string_view timeSuffix(std::string_view time1, std::string_view time2);

	TimerThread::Handle TimerThread::scheduleTask(
	std::string_view tag, TimerCallback&& func,
	Duration timeoutDuration, Duration secondChanceDuration) {
	const auto now = std::chrono::system_clock::now();
	auto request = std::make_shared<const Request>(now, now +
	std::chrono::duration_cast<std::chrono::system_clock::duration>(timeoutDuration),
	secondChanceDuration, getThreadIdWrapper(), tag);
	return mMonitorThread.add(std::move(request), std::move(func), timeoutDuration);
	}

	TimerThread::Handle TimerThread::trackTask(std::string_view tag) {
	const auto now = std::chrono::system_clock::now();
	auto request = std::make_shared<const Request>(now, now,
	Duration{} /* secondChanceDuration */, getThreadIdWrapper(), tag);
	return mNoTimeoutMap.add(std::move(request));
	}

	bool TimerThread::cancelTask(Handle handle) {
	std::shared_ptr<const Request> request = isNoTimeoutHandle(handle) ?
	mNoTimeoutMap.remove(handle) : mMonitorThread.remove(handle);
	if (!request) return false;
	mRetiredQueue.add(std::move(request));
	return true;
	}


	std::string TimerThread::SnapshotAnalysis::toString() const {
	// Note: These request queues are snapshot very close together but
	// not at "identical" times as we don't use a class-wide lock.
	std::string analysisSummary = std::string("\nanalysis [ ").append(description).append(" ]");
	std::string timeoutStack;
	std::string blockedStack;
	if (timeoutTid != -1) {
	timeoutStack = std::string(suspectTid == timeoutTid ? "\ntimeout/blocked(" : "\ntimeout(")
	.append(std::to_string(timeoutTid)).append(") callstack [\n")
	.append(getCallStackStringForTid(timeoutTid)).append("]");
	}

	if (suspectTid != -1 && suspectTid != timeoutTid) {
	blockedStack = std::string("\nblocked(")
	.append(std::to_string(suspectTid)).append(") callstack [\n")
	.append(getCallStackStringForTid(suspectTid)).append("]");
	}

	return std::string("now ")
	.append(formatTime(std::chrono::system_clock::now()))
	.append("\nsecondChanceCount ")
	.append(std::to_string(secondChanceCount))
	.append(analysisSummary)
	.append("\ntimeout [ ")
	.append(requestsToString(timeoutRequests))
	.append(" ]\npending [ ")
	.append(requestsToString(pendingRequests))
	.append(" ]\nretired [ ")
	.append(requestsToString(retiredRequests))
	.append(" ]")
	.append(timeoutStack)
	.append(blockedStack);
	}

	// A HAL method is where the substring "Hidl" is in the class name.
	// The tag should look like: ... Hidl ... :: ...
	// When the audio HAL is updated to AIDL perhaps we will use instead
	// a global directory of HAL classes.
	//
	// See MethodStatistics.cpp:
	// mediautils::getStatisticsClassesForModule(METHOD_STATISTICS_MODULE_NAME_AUDIO_HIDL)
	//
	/* static */
	bool TimerThread::isRequestFromHal(const std::shared_ptr<const Request>& request) {
	const size_t hidlPos = request->tag.asStringView().find("Hidl");
	if (hidlPos == std::string::npos) return false;
	// should be a separator afterwards Hidl which indicates the string was in the class.
	const size_t separatorPos = request->tag.asStringView().find("::", hidlPos);
	return separatorPos != std::string::npos;
	}

	struct TimerThread::SnapshotAnalysis TimerThread::getSnapshotAnalysis(size_t retiredCount) const {
	struct SnapshotAnalysis analysis{};
	// The following snapshot of the TimerThread state will be utilized for
	// analysis. Note, there is no lock around these calls, so there could be
	// a state update between them.
	mTimeoutQueue.copyRequests(analysis.timeoutRequests);
	mRetiredQueue.copyRequests(analysis.retiredRequests, retiredCount);
	analysis.pendingRequests = getPendingRequests();
	analysis.secondChanceCount = mMonitorThread.getSecondChanceCount();
	// No call has timed out, so there is no analysis to be done.
	if (analysis.timeoutRequests.empty())
	return analysis;
	// for now look at last timeout (in our case, the only timeout)
	const std::shared_ptr<const Request> timeout = analysis.timeoutRequests.back();
	analysis.timeoutTid = timeout->tid;
	if (analysis.pendingRequests.empty())
	return analysis;
	// pending Requests that are problematic.
	std::vector<std::shared_ptr<const Request>> pendingExact;
	std::vector<std::shared_ptr<const Request>> pendingPossible;

	// We look at pending requests that were scheduled no later than kPendingDuration
	// after the timeout request. This prevents false matches with calls
	// that naturally block for a short period of time
	// such as HAL write() and read().
	//
	constexpr Duration kPendingDuration = 1000ms;
	for (const auto& pending : analysis.pendingRequests) {
	// If the pending tid is the same as timeout tid, problem identified.
	if (pending->tid == timeout->tid) {
	pendingExact.emplace_back(pending);
	continue;
	}

	// if the pending tid is scheduled within time limit
	if (pending->scheduled - timeout->scheduled < kPendingDuration) {
	pendingPossible.emplace_back(pending);
	}
	}

	std::string& description = analysis.description;
	if (!pendingExact.empty()) {
	const auto& request = pendingExact.front();
	const bool hal = isRequestFromHal(request);

	if (hal) {
	description = std::string("Blocked directly due to HAL call: ")
	.append(request->toString());
	analysis.suspectTid= request->tid;
	}
	}
	if (description.empty() && !pendingPossible.empty()) {
	for (const auto& request : pendingPossible) {
	const bool hal = isRequestFromHal(request);
	if (hal) {
	// The first blocked call is the most likely one.
	// Recent calls might be temporarily blocked
	// calls such as write() or read() depending on kDuration.
	description = std::string("Blocked possibly due to HAL call: ")
	.append(request->toString());
	analysis.suspectTid= request->tid;
	}
	}
	}
	return analysis;
	}

	std::vector<std::shared_ptr<const TimerThread::Request>> TimerThread::getPendingRequests() const {
	constexpr size_t kEstimatedPendingRequests = 8; // approx 128 byte alloc.
	std::vector<std::shared_ptr<const Request>> pendingRequests;
	pendingRequests.reserve(kEstimatedPendingRequests); // preallocate vector out of lock.

	// following are internally locked calls, which add to our local pendingRequests.
	mMonitorThread.copyRequests(pendingRequests);
	mNoTimeoutMap.copyRequests(pendingRequests);

	// Sort in order of scheduled time.
	std::sort(pendingRequests.begin(), pendingRequests.end(),
	[](const std::shared_ptr<const Request>& r1,
	const std::shared_ptr<const Request>& r2) {
	return r1->scheduled < r2->scheduled;
	});
	return pendingRequests;
	}

	std::string TimerThread::pendingToString() const {
	return requestsToString(getPendingRequests());
	}

	std::string TimerThread::retiredToString(size_t n) const {
	std::vector<std::shared_ptr<const Request>> retiredRequests;
	mRetiredQueue.copyRequests(retiredRequests, n);

	// Dump to string
	return requestsToString(retiredRequests);
	}

	std::string TimerThread::timeoutToString(size_t n) const {
	std::vector<std::shared_ptr<const Request>> timeoutRequests;
	mTimeoutQueue.copyRequests(timeoutRequests, n);

	// Dump to string
	return requestsToString(timeoutRequests);
	}

	std::string TimerThread::Request::toString() const {
	const auto scheduledString = formatTime(scheduled);
	const auto deadlineString = formatTime(deadline);
	return std::string(tag)
	.append(" scheduled ").append(scheduledString)
	.append(" deadline ").append(timeSuffix(scheduledString, deadlineString))
	.append(" tid ").append(std::to_string(tid));
	}

	void TimerThread::RequestQueue::add(std::shared_ptr<const Request> request) {
	std::lock_guard lg(mRQMutex);
	mRequestQueue.emplace_back(std::chrono::system_clock::now(), std::move(request));
	if (mRequestQueue.size() > mRequestQueueMax) {
	mRequestQueue.pop_front();
	}
	}

	void TimerThread::RequestQueue::copyRequests(
	std::vector<std::shared_ptr<const Request>>& requests, size_t n) const {
	std::lock_guard lg(mRQMutex);
	const size_t size = mRequestQueue.size();
	size_t i = n >= size ? 0 : size - n;
	for (; i < size; ++i) {
	const auto &[time, request] = mRequestQueue[i];
	requests.emplace_back(request);
	}
	}

	TimerThread::Handle TimerThread::NoTimeoutMap::add(std::shared_ptr<const Request> request) {
	std::lock_guard lg(mNTMutex);
	// A unique handle is obtained by mNoTimeoutRequests.fetch_add(1),
	// This need not be under a lock, but we do so anyhow.
	const Handle handle = getUniqueHandle_l();
	mMap[handle] = request;
	return handle;
	}

	std::shared_ptr<const TimerThread::Request> TimerThread::NoTimeoutMap::remove(Handle handle) {
	std::lock_guard lg(mNTMutex);
	auto it = mMap.find(handle);
	if (it == mMap.end()) return {};
	auto request = it->second;
	mMap.erase(it);
	return request;
	}

	void TimerThread::NoTimeoutMap::copyRequests(
	std::vector<std::shared_ptr<const Request>>& requests) const {
	std::lock_guard lg(mNTMutex);
	for (const auto &[handle, request] : mMap) {
	requests.emplace_back(request);
	}
	}

	TimerThread::MonitorThread::MonitorThread(RequestQueue& timeoutQueue)
	: mTimeoutQueue(timeoutQueue)
	, mThread([this] { threadFunc(); }) {
	pthread_setname_np(mThread.native_handle(), "TimerThread");
	pthread_setschedprio(mThread.native_handle(), PRIORITY_URGENT_AUDIO);
	}

	TimerThread::MonitorThread::~MonitorThread() {
	{
	std::lock_guard _l(mMutex);
	mShouldExit = true;
	mCond.notify_all();
	}
	mThread.join();
	}

	void TimerThread::MonitorThread::threadFunc() {
	std::unique_lock _l(mMutex);
	::android::base::ScopedLockAssertion lock_assertion(mMutex);
	while (!mShouldExit) {
	Handle nextDeadline = INVALID_HANDLE;
	Handle now = INVALID_HANDLE;
	if (!mMonitorRequests.empty()) {
	nextDeadline = mMonitorRequests.begin()->first;
	now = std::chrono::steady_clock::now();
	if (nextDeadline < now) {
	auto node = mMonitorRequests.extract(mMonitorRequests.begin());
	// Deadline has expired, handle the request.
	auto secondChanceDuration = node.mapped().first->secondChanceDuration;
	if (secondChanceDuration.count() != 0) {
	// We now apply the second chance duration to find the clock
	// monotonic second deadline. The unique key is then the
	// pair<second_deadline, first_deadline>.
	//
	// The second chance prevents a false timeout should there be
	// any clock monotonic advancement during suspend.
	auto newHandle = now + secondChanceDuration;
	ALOGD("%s: TimeCheck second chance applied for %s",
	__func__, node.mapped().first->tag.c_str()); // should be rare event.
	mSecondChanceRequests.emplace_hint(mSecondChanceRequests.end(),
	std::make_pair(newHandle, nextDeadline),
	std::move(node.mapped()));
	// increment second chance counter.
	mSecondChanceCount.fetch_add(1 /* arg */, std::memory_order_relaxed);
	} else {
	{
	_l.unlock();
	// We add Request to retired queue early so that it can be dumped out.
	mTimeoutQueue.add(std::move(node.mapped().first));
	node.mapped().second(nextDeadline);
	// Caution: we don't hold lock when we call TimerCallback,
	// but this is the timeout case! We will crash soon,
	// maybe before returning.
	// anything left over is released here outside lock.
	}
	// reacquire the lock - if something was added, we loop immediately to check.
	_l.lock();
	}
	// always process expiring monitor requests first.
	continue;
	}
	}
	// now process any second chance requests.
	if (!mSecondChanceRequests.empty()) {
	Handle secondDeadline = mSecondChanceRequests.begin()->first.first;
	if (now == INVALID_HANDLE) now = std::chrono::steady_clock::now();
	if (secondDeadline < now) {
	auto node = mSecondChanceRequests.extract(mSecondChanceRequests.begin());
	{
	_l.unlock();
	// We add Request to retired queue early so that it can be dumped out.
	mTimeoutQueue.add(std::move(node.mapped().first));
	const Handle originalHandle = node.key().second;
	node.mapped().second(originalHandle);
	// Caution: we don't hold lock when we call TimerCallback.
	// This is benign issue - we permit concurrent operations
	// while in the callback to the MonitorQueue.
	//
	// Anything left over is released here outside lock.
	}
	// reacquire the lock - if something was added, we loop immediately to check.
	_l.lock();
	continue;
	}
	// update the deadline.
	if (nextDeadline == INVALID_HANDLE) {
	nextDeadline = secondDeadline;
	} else {
	nextDeadline = std::min(nextDeadline, secondDeadline);
	}
	}
	if (nextDeadline != INVALID_HANDLE) {
	mCond.wait_until(_l, nextDeadline);
	} else {
	mCond.wait(_l);
	}
	}
	}

	TimerThread::Handle TimerThread::MonitorThread::add(
	std::shared_ptr<const Request> request, TimerCallback&& func, Duration timeout) {
	std::lock_guard _l(mMutex);
	const Handle handle = getUniqueHandle_l(timeout);
	mMonitorRequests.emplace_hint(mMonitorRequests.end(),
	handle, std::make_pair(std::move(request), std::move(func)));
	mCond.notify_all();
	return handle;
	}

	std::shared_ptr<const TimerThread::Request> TimerThread::MonitorThread::remove(Handle handle) {
	std::pair<std::shared_ptr<const Request>, TimerCallback> data;
	std::unique_lock ul(mMutex);
	::android::base::ScopedLockAssertion lock_assertion(mMutex);
	if (const auto it = mMonitorRequests.find(handle);
	it != mMonitorRequests.end()) {
	data = std::move(it->second);
	mMonitorRequests.erase(it);
	ul.unlock(); // manually release lock here so func (data.second)
	// is released outside of lock.
	return data.first; // request
	}

	// this check is O(N), but since the second chance requests are ordered
	// in terms of earliest expiration time, we would expect better than average results.
	for (auto it = mSecondChanceRequests.begin(); it != mSecondChanceRequests.end(); ++it) {
	if (it->first.second == handle) {
	data = std::move(it->second);
	mSecondChanceRequests.erase(it);
	ul.unlock(); // manually release lock here so func (data.second)
	// is released outside of lock.
	return data.first; // request
	}
	}
	return {};
	}

	void TimerThread::MonitorThread::copyRequests(
	std::vector<std::shared_ptr<const Request>>& requests) const {
	std::lock_guard lg(mMutex);
	for (const auto &[deadline, monitorpair] : mMonitorRequests) {
	requests.emplace_back(monitorpair.first);
	}
	// we combine the second map with the first map - this is
	// everything that is pending on the monitor thread.
	// The second map will be older than the first map so this
	// is in order.
	for (const auto &[deadline, monitorpair] : mSecondChanceRequests) {
	requests.emplace_back(monitorpair.first);
	}
	}

	} // namespace android::mediautils