native/android/performance_hint.cpp - android_frameworks_base - Gitiles

 /*
  * 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 "perf_hint"

 #include <aidl/android/hardware/power/SessionHint.h>
 #include <android/os/IHintManager.h>
 #include <android/os/IHintSession.h>
 #include <android/performance_hint.h>
 #include <binder/Binder.h>
 #include <binder/IBinder.h>
 #include <binder/IServiceManager.h>
 #include <performance_hint_private.h>
 #include <utils/SystemClock.h>

 #include <chrono>
 #include <utility>
 #include <vector>

 using namespace android;
 using namespace android::os;

 using namespace std::chrono_literals;

 using AidlSessionHint = aidl::android::hardware::power::SessionHint;

 struct APerformanceHintSession;

 constexpr int64_t SEND_HINT_TIMEOUT = std::chrono::nanoseconds(100ms).count();

 struct APerformanceHintManager {
 public:
     static APerformanceHintManager* getInstance();
     APerformanceHintManager(sp<IHintManager> service, int64_t preferredRateNanos);
     APerformanceHintManager() = delete;
     ~APerformanceHintManager() = default;

     APerformanceHintSession* createSession(const int32_t* threadIds, size_t size,
                                            int64_t initialTargetWorkDurationNanos);
     int64_t getPreferredRateNanos() const;

 private:
     static APerformanceHintManager* create(sp<IHintManager> iHintManager);

     sp<IHintManager> mHintManager;
     const sp<IBinder> mToken = sp<BBinder>::make();
     const int64_t mPreferredRateNanos;
 };

 struct APerformanceHintSession {
 public:
     APerformanceHintSession(sp<IHintManager> hintManager, sp<IHintSession> session,
                             int64_t preferredRateNanos, int64_t targetDurationNanos);
     APerformanceHintSession() = delete;
     ~APerformanceHintSession();

     int updateTargetWorkDuration(int64_t targetDurationNanos);
     int reportActualWorkDuration(int64_t actualDurationNanos);
     int sendHint(SessionHint hint);
     int setThreads(const int32_t* threadIds, size_t size);
     int getThreadIds(int32_t* const threadIds, size_t* size);

 private:
     friend struct APerformanceHintManager;

     sp<IHintManager> mHintManager;
     sp<IHintSession> mHintSession;
     // HAL preferred update rate
     const int64_t mPreferredRateNanos;
     // Target duration for choosing update rate
     int64_t mTargetDurationNanos;
     // First target hit timestamp
     int64_t mFirstTargetMetTimestamp;
     // Last target hit timestamp
     int64_t mLastTargetMetTimestamp;
     // Last hint reported from sendHint indexed by hint value
     std::vector<int64_t> mLastHintSentTimestamp;
     // Cached samples
     std::vector<int64_t> mActualDurationsNanos;
     std::vector<int64_t> mTimestampsNanos;
 };

 static IHintManager* gIHintManagerForTesting = nullptr;
 static APerformanceHintManager* gHintManagerForTesting = nullptr;

 // ===================================== APerformanceHintManager implementation
 APerformanceHintManager::APerformanceHintManager(sp<IHintManager> manager,
                                                  int64_t preferredRateNanos)
       : mHintManager(std::move(manager)), mPreferredRateNanos(preferredRateNanos) {}

 APerformanceHintManager* APerformanceHintManager::getInstance() {
     if (gHintManagerForTesting) return gHintManagerForTesting;
     if (gIHintManagerForTesting) {
         APerformanceHintManager* manager = create(gIHintManagerForTesting);
         gIHintManagerForTesting = nullptr;
         return manager;
     }
     static APerformanceHintManager* instance = create(nullptr);
     return instance;
 }

 APerformanceHintManager* APerformanceHintManager::create(sp<IHintManager> manager) {
     if (!manager) {
         manager = interface_cast<IHintManager>(
                 defaultServiceManager()->checkService(String16("performance_hint")));
     }
     if (manager == nullptr) {
         ALOGE("%s: PerformanceHint service is not ready ", __FUNCTION__);
         return nullptr;
     }
     int64_t preferredRateNanos = -1L;
     binder::Status ret = manager->getHintSessionPreferredRate(&preferredRateNanos);
     if (!ret.isOk()) {
         ALOGE("%s: PerformanceHint cannot get preferred rate. %s", __FUNCTION__,
               ret.exceptionMessage().c_str());
         return nullptr;
     }
     if (preferredRateNanos <= 0) {
         preferredRateNanos = -1L;
     }
     return new APerformanceHintManager(std::move(manager), preferredRateNanos);
 }

 APerformanceHintSession* APerformanceHintManager::createSession(
         const int32_t* threadIds, size_t size, int64_t initialTargetWorkDurationNanos) {
     std::vector<int32_t> tids(threadIds, threadIds + size);
     sp<IHintSession> session;
     binder::Status ret =
             mHintManager->createHintSession(mToken, tids, initialTargetWorkDurationNanos, &session);
     if (!ret.isOk() || !session) {
         return nullptr;
     }
     return new APerformanceHintSession(mHintManager, std::move(session), mPreferredRateNanos,
                                        initialTargetWorkDurationNanos);
 }

 int64_t APerformanceHintManager::getPreferredRateNanos() const {
     return mPreferredRateNanos;
 }

 // ===================================== APerformanceHintSession implementation

 APerformanceHintSession::APerformanceHintSession(sp<IHintManager> hintManager,
                                                  sp<IHintSession> session,
                                                  int64_t preferredRateNanos,
                                                  int64_t targetDurationNanos)
       : mHintManager(hintManager),
         mHintSession(std::move(session)),
         mPreferredRateNanos(preferredRateNanos),
         mTargetDurationNanos(targetDurationNanos),
         mFirstTargetMetTimestamp(0),
         mLastTargetMetTimestamp(0) {
     const std::vector<AidlSessionHint> sessionHintRange{ndk::enum_range<AidlSessionHint>().begin(),
                                                         ndk::enum_range<AidlSessionHint>().end()};

     mLastHintSentTimestamp = std::vector<int64_t>(sessionHintRange.size(), 0);
 }

 APerformanceHintSession::~APerformanceHintSession() {
     binder::Status ret = mHintSession->close();
     if (!ret.isOk()) {
         ALOGE("%s: HintSession close failed: %s", __FUNCTION__, ret.exceptionMessage().c_str());
     }
 }

 int APerformanceHintSession::updateTargetWorkDuration(int64_t targetDurationNanos) {
     if (targetDurationNanos <= 0) {
         ALOGE("%s: targetDurationNanos must be positive", __FUNCTION__);
         return EINVAL;
     }
     binder::Status ret = mHintSession->updateTargetWorkDuration(targetDurationNanos);
     if (!ret.isOk()) {
         ALOGE("%s: HintSession updateTargetWorkDuration failed: %s", __FUNCTION__,
               ret.exceptionMessage().c_str());
         return EPIPE;
     }
     mTargetDurationNanos = targetDurationNanos;
     /**
      * Most of the workload is target_duration dependent, so now clear the cached samples
      * as they are most likely obsolete.
      */
     mActualDurationsNanos.clear();
     mTimestampsNanos.clear();
     mFirstTargetMetTimestamp = 0;
     mLastTargetMetTimestamp = 0;
     return 0;
 }

 int APerformanceHintSession::reportActualWorkDuration(int64_t actualDurationNanos) {
     if (actualDurationNanos <= 0) {
         ALOGE("%s: actualDurationNanos must be positive", __FUNCTION__);
         return EINVAL;
     }
     int64_t now = elapsedRealtimeNano();
     mActualDurationsNanos.push_back(actualDurationNanos);
     mTimestampsNanos.push_back(now);

     if (actualDurationNanos >= mTargetDurationNanos) {
         // Reset timestamps if we are equal or over the target.
         mFirstTargetMetTimestamp = 0;
     } else {
         // Set mFirstTargetMetTimestamp for first time meeting target.
         if (!mFirstTargetMetTimestamp || !mLastTargetMetTimestamp ||
             (now - mLastTargetMetTimestamp > 2 * mPreferredRateNanos)) {
             mFirstTargetMetTimestamp = now;
         }
         /**
          * Rate limit the change if the update is over mPreferredRateNanos since first
          * meeting target and less than mPreferredRateNanos since last meeting target.
          */
         if (now - mFirstTargetMetTimestamp > mPreferredRateNanos &&
             now - mLastTargetMetTimestamp <= mPreferredRateNanos) {
             return 0;
         }
         mLastTargetMetTimestamp = now;
     }

     binder::Status ret =
             mHintSession->reportActualWorkDuration(mActualDurationsNanos, mTimestampsNanos);
     if (!ret.isOk()) {
         ALOGE("%s: HintSession reportActualWorkDuration failed: %s", __FUNCTION__,
               ret.exceptionMessage().c_str());
         mFirstTargetMetTimestamp = 0;
         mLastTargetMetTimestamp = 0;
         return EPIPE;
     }
     mActualDurationsNanos.clear();
     mTimestampsNanos.clear();

     return 0;
 }

 int APerformanceHintSession::sendHint(SessionHint hint) {
     if (hint < 0 || hint >= static_cast<int32_t>(mLastHintSentTimestamp.size())) {
         ALOGE("%s: invalid session hint %d", __FUNCTION__, hint);
         return EINVAL;
     }
     int64_t now = elapsedRealtimeNano();

     // Limit sendHint to a pre-detemined rate for safety
     if (now < (mLastHintSentTimestamp[hint] + SEND_HINT_TIMEOUT)) {
         return 0;
     }

     binder::Status ret = mHintSession->sendHint(hint);

     if (!ret.isOk()) {
         ALOGE("%s: HintSession sendHint failed: %s", __FUNCTION__, ret.exceptionMessage().c_str());
         return EPIPE;
     }
     mLastHintSentTimestamp[hint] = now;
     return 0;
 }

 int APerformanceHintSession::setThreads(const int32_t* threadIds, size_t size) {
     if (size == 0) {
         ALOGE("%s: the list of thread ids must not be empty.", __FUNCTION__);
         return EINVAL;
     }
     std::vector<int32_t> tids(threadIds, threadIds + size);
     binder::Status ret = mHintManager->setHintSessionThreads(mHintSession, tids);
     if (!ret.isOk()) {
         ALOGE("%s: failed: %s", __FUNCTION__, ret.exceptionMessage().c_str());
         if (ret.exceptionCode() == binder::Status::Exception::EX_SECURITY ||
             ret.exceptionCode() == binder::Status::Exception::EX_ILLEGAL_ARGUMENT) {
             return EINVAL;
         }
         return EPIPE;
     }
     return 0;
 }

 int APerformanceHintSession::getThreadIds(int32_t* const threadIds, size_t* size) {
     std::vector<int32_t> tids;
     binder::Status ret = mHintManager->getHintSessionThreadIds(mHintSession, &tids);
     if (!ret.isOk()) {
         ALOGE("%s: failed: %s", __FUNCTION__, ret.exceptionMessage().c_str());
         return EPIPE;
     }

     // When threadIds is nullptr, this is the first call to determine the size
     // of the thread ids list.
     if (threadIds == nullptr) {
         *size = tids.size();
         return 0;
     }

     // Second call to return the actual list of thread ids.
     *size = tids.size();
     for (size_t i = 0; i < *size; ++i) {
         threadIds[i] = tids[i];
     }
     return 0;
 }

 // ===================================== C API
 APerformanceHintManager* APerformanceHint_getManager() {
     return APerformanceHintManager::getInstance();
 }

 APerformanceHintSession* APerformanceHint_createSession(APerformanceHintManager* manager,
                                                         const int32_t* threadIds, size_t size,
                                                         int64_t initialTargetWorkDurationNanos) {
     return manager->createSession(threadIds, size, initialTargetWorkDurationNanos);
 }

 int64_t APerformanceHint_getPreferredUpdateRateNanos(APerformanceHintManager* manager) {
     return manager->getPreferredRateNanos();
 }

 int APerformanceHint_updateTargetWorkDuration(APerformanceHintSession* session,
                                               int64_t targetDurationNanos) {
     return session->updateTargetWorkDuration(targetDurationNanos);
 }

 int APerformanceHint_reportActualWorkDuration(APerformanceHintSession* session,
                                               int64_t actualDurationNanos) {
     return session->reportActualWorkDuration(actualDurationNanos);
 }

 void APerformanceHint_closeSession(APerformanceHintSession* session) {
     delete session;
 }

 int APerformanceHint_sendHint(void* session, SessionHint hint) {
     return reinterpret_cast<APerformanceHintSession*>(session)->sendHint(hint);
 }

 int APerformanceHint_setThreads(APerformanceHintSession* session, const pid_t* threadIds,
                                 size_t size) {
     if (session == nullptr) {
         return EINVAL;
     }
     return session->setThreads(threadIds, size);
 }

 int APerformanceHint_getThreadIds(void* aPerformanceHintSession, int32_t* const threadIds,
                                   size_t* const size) {
     if (aPerformanceHintSession == nullptr) {
         return EINVAL;
     }
     return static_cast<APerformanceHintSession*>(aPerformanceHintSession)
             ->getThreadIds(threadIds, size);
 }

 void APerformanceHint_setIHintManagerForTesting(void* iManager) {
     delete gHintManagerForTesting;
     gHintManagerForTesting = nullptr;
     gIHintManagerForTesting = static_cast<IHintManager*>(iManager);
 }
	/*
	* 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 "perf_hint"

	#include <aidl/android/hardware/power/SessionHint.h>
	#include <android/os/IHintManager.h>
	#include <android/os/IHintSession.h>
	#include <android/performance_hint.h>
	#include <binder/Binder.h>
	#include <binder/IBinder.h>
	#include <binder/IServiceManager.h>
	#include <performance_hint_private.h>
	#include <utils/SystemClock.h>

	#include <chrono>
	#include <utility>
	#include <vector>

	using namespace android;
	using namespace android::os;

	using namespace std::chrono_literals;

	using AidlSessionHint = aidl::android::hardware::power::SessionHint;

	struct APerformanceHintSession;

	constexpr int64_t SEND_HINT_TIMEOUT = std::chrono::nanoseconds(100ms).count();

	struct APerformanceHintManager {
	public:
	static APerformanceHintManager* getInstance();
	APerformanceHintManager(sp<IHintManager> service, int64_t preferredRateNanos);
	APerformanceHintManager() = delete;
	~APerformanceHintManager() = default;

	APerformanceHintSession* createSession(const int32_t* threadIds, size_t size,
	int64_t initialTargetWorkDurationNanos);
	int64_t getPreferredRateNanos() const;

	private:
	static APerformanceHintManager* create(sp<IHintManager> iHintManager);

	sp<IHintManager> mHintManager;
	const sp<IBinder> mToken = sp<BBinder>::make();
	const int64_t mPreferredRateNanos;
	};

	struct APerformanceHintSession {
	public:
	APerformanceHintSession(sp<IHintManager> hintManager, sp<IHintSession> session,
	int64_t preferredRateNanos, int64_t targetDurationNanos);
	APerformanceHintSession() = delete;
	~APerformanceHintSession();

	int updateTargetWorkDuration(int64_t targetDurationNanos);
	int reportActualWorkDuration(int64_t actualDurationNanos);
	int sendHint(SessionHint hint);
	int setThreads(const int32_t* threadIds, size_t size);
	int getThreadIds(int32_t* const threadIds, size_t* size);

	private:
	friend struct APerformanceHintManager;

	sp<IHintManager> mHintManager;
	sp<IHintSession> mHintSession;
	// HAL preferred update rate
	const int64_t mPreferredRateNanos;
	// Target duration for choosing update rate
	int64_t mTargetDurationNanos;
	// First target hit timestamp
	int64_t mFirstTargetMetTimestamp;
	// Last target hit timestamp
	int64_t mLastTargetMetTimestamp;
	// Last hint reported from sendHint indexed by hint value
	std::vector<int64_t> mLastHintSentTimestamp;
	// Cached samples
	std::vector<int64_t> mActualDurationsNanos;
	std::vector<int64_t> mTimestampsNanos;
	};

	static IHintManager* gIHintManagerForTesting = nullptr;
	static APerformanceHintManager* gHintManagerForTesting = nullptr;

	// ===================================== APerformanceHintManager implementation
	APerformanceHintManager::APerformanceHintManager(sp<IHintManager> manager,
	int64_t preferredRateNanos)
	: mHintManager(std::move(manager)), mPreferredRateNanos(preferredRateNanos) {}

	APerformanceHintManager* APerformanceHintManager::getInstance() {
	if (gHintManagerForTesting) return gHintManagerForTesting;
	if (gIHintManagerForTesting) {
	APerformanceHintManager* manager = create(gIHintManagerForTesting);
	gIHintManagerForTesting = nullptr;
	return manager;
	}
	static APerformanceHintManager* instance = create(nullptr);
	return instance;
	}

	APerformanceHintManager* APerformanceHintManager::create(sp<IHintManager> manager) {
	if (!manager) {
	manager = interface_cast<IHintManager>(
	defaultServiceManager()->checkService(String16("performance_hint")));
	}
	if (manager == nullptr) {
	ALOGE("%s: PerformanceHint service is not ready ", __FUNCTION__);
	return nullptr;
	}
	int64_t preferredRateNanos = -1L;
	binder::Status ret = manager->getHintSessionPreferredRate(&preferredRateNanos);
	if (!ret.isOk()) {
	ALOGE("%s: PerformanceHint cannot get preferred rate. %s", __FUNCTION__,
	ret.exceptionMessage().c_str());
	return nullptr;
	}
	if (preferredRateNanos <= 0) {
	preferredRateNanos = -1L;
	}
	return new APerformanceHintManager(std::move(manager), preferredRateNanos);
	}

	APerformanceHintSession* APerformanceHintManager::createSession(
	const int32_t* threadIds, size_t size, int64_t initialTargetWorkDurationNanos) {
	std::vector<int32_t> tids(threadIds, threadIds + size);
	sp<IHintSession> session;
	binder::Status ret =
	mHintManager->createHintSession(mToken, tids, initialTargetWorkDurationNanos, &session);
	if (!ret.isOk() \|\| !session) {
	return nullptr;
	}
	return new APerformanceHintSession(mHintManager, std::move(session), mPreferredRateNanos,
	initialTargetWorkDurationNanos);
	}

	int64_t APerformanceHintManager::getPreferredRateNanos() const {
	return mPreferredRateNanos;
	}

	// ===================================== APerformanceHintSession implementation

	APerformanceHintSession::APerformanceHintSession(sp<IHintManager> hintManager,
	sp<IHintSession> session,
	int64_t preferredRateNanos,
	int64_t targetDurationNanos)
	: mHintManager(hintManager),
	mHintSession(std::move(session)),
	mPreferredRateNanos(preferredRateNanos),
	mTargetDurationNanos(targetDurationNanos),
	mFirstTargetMetTimestamp(0),
	mLastTargetMetTimestamp(0) {
	const std::vector<AidlSessionHint> sessionHintRange{ndk::enum_range<AidlSessionHint>().begin(),
	ndk::enum_range<AidlSessionHint>().end()};

	mLastHintSentTimestamp = std::vector<int64_t>(sessionHintRange.size(), 0);
	}

	APerformanceHintSession::~APerformanceHintSession() {
	binder::Status ret = mHintSession->close();
	if (!ret.isOk()) {
	ALOGE("%s: HintSession close failed: %s", __FUNCTION__, ret.exceptionMessage().c_str());
	}
	}

	int APerformanceHintSession::updateTargetWorkDuration(int64_t targetDurationNanos) {
	if (targetDurationNanos <= 0) {
	ALOGE("%s: targetDurationNanos must be positive", __FUNCTION__);
	return EINVAL;
	}
	binder::Status ret = mHintSession->updateTargetWorkDuration(targetDurationNanos);
	if (!ret.isOk()) {
	ALOGE("%s: HintSession updateTargetWorkDuration failed: %s", __FUNCTION__,
	ret.exceptionMessage().c_str());
	return EPIPE;
	}
	mTargetDurationNanos = targetDurationNanos;
	/**
	* Most of the workload is target_duration dependent, so now clear the cached samples
	* as they are most likely obsolete.
	*/
	mActualDurationsNanos.clear();
	mTimestampsNanos.clear();
	mFirstTargetMetTimestamp = 0;
	mLastTargetMetTimestamp = 0;
	return 0;
	}

	int APerformanceHintSession::reportActualWorkDuration(int64_t actualDurationNanos) {
	if (actualDurationNanos <= 0) {
	ALOGE("%s: actualDurationNanos must be positive", __FUNCTION__);
	return EINVAL;
	}
	int64_t now = elapsedRealtimeNano();
	mActualDurationsNanos.push_back(actualDurationNanos);
	mTimestampsNanos.push_back(now);

	if (actualDurationNanos >= mTargetDurationNanos) {
	// Reset timestamps if we are equal or over the target.
	mFirstTargetMetTimestamp = 0;
	} else {
	// Set mFirstTargetMetTimestamp for first time meeting target.
	if (!mFirstTargetMetTimestamp \|\| !mLastTargetMetTimestamp \|\|
	(now - mLastTargetMetTimestamp > 2 * mPreferredRateNanos)) {
	mFirstTargetMetTimestamp = now;
	}
	/**
	* Rate limit the change if the update is over mPreferredRateNanos since first
	* meeting target and less than mPreferredRateNanos since last meeting target.
	*/
	if (now - mFirstTargetMetTimestamp > mPreferredRateNanos &&
	now - mLastTargetMetTimestamp <= mPreferredRateNanos) {
	return 0;
	}
	mLastTargetMetTimestamp = now;
	}

	binder::Status ret =
	mHintSession->reportActualWorkDuration(mActualDurationsNanos, mTimestampsNanos);
	if (!ret.isOk()) {
	ALOGE("%s: HintSession reportActualWorkDuration failed: %s", __FUNCTION__,
	ret.exceptionMessage().c_str());
	mFirstTargetMetTimestamp = 0;
	mLastTargetMetTimestamp = 0;
	return EPIPE;
	}
	mActualDurationsNanos.clear();
	mTimestampsNanos.clear();

	return 0;
	}

	int APerformanceHintSession::sendHint(SessionHint hint) {
	if (hint < 0 \|\| hint >= static_cast<int32_t>(mLastHintSentTimestamp.size())) {
	ALOGE("%s: invalid session hint %d", __FUNCTION__, hint);
	return EINVAL;
	}
	int64_t now = elapsedRealtimeNano();

	// Limit sendHint to a pre-detemined rate for safety
	if (now < (mLastHintSentTimestamp[hint] + SEND_HINT_TIMEOUT)) {
	return 0;
	}

	binder::Status ret = mHintSession->sendHint(hint);

	if (!ret.isOk()) {
	ALOGE("%s: HintSession sendHint failed: %s", __FUNCTION__, ret.exceptionMessage().c_str());
	return EPIPE;
	}
	mLastHintSentTimestamp[hint] = now;
	return 0;
	}

	int APerformanceHintSession::setThreads(const int32_t* threadIds, size_t size) {
	if (size == 0) {
	ALOGE("%s: the list of thread ids must not be empty.", __FUNCTION__);
	return EINVAL;
	}
	std::vector<int32_t> tids(threadIds, threadIds + size);
	binder::Status ret = mHintManager->setHintSessionThreads(mHintSession, tids);
	if (!ret.isOk()) {
	ALOGE("%s: failed: %s", __FUNCTION__, ret.exceptionMessage().c_str());
	if (ret.exceptionCode() == binder::Status::Exception::EX_SECURITY \|\|
	ret.exceptionCode() == binder::Status::Exception::EX_ILLEGAL_ARGUMENT) {
	return EINVAL;
	}
	return EPIPE;
	}
	return 0;
	}

	int APerformanceHintSession::getThreadIds(int32_t* const threadIds, size_t* size) {
	std::vector<int32_t> tids;
	binder::Status ret = mHintManager->getHintSessionThreadIds(mHintSession, &tids);
	if (!ret.isOk()) {
	ALOGE("%s: failed: %s", __FUNCTION__, ret.exceptionMessage().c_str());
	return EPIPE;
	}

	// When threadIds is nullptr, this is the first call to determine the size
	// of the thread ids list.
	if (threadIds == nullptr) {
	*size = tids.size();
	return 0;
	}

	// Second call to return the actual list of thread ids.
	*size = tids.size();
	for (size_t i = 0; i < *size; ++i) {
	threadIds[i] = tids[i];
	}
	return 0;
	}

	// ===================================== C API
	APerformanceHintManager* APerformanceHint_getManager() {
	return APerformanceHintManager::getInstance();
	}

	APerformanceHintSession* APerformanceHint_createSession(APerformanceHintManager* manager,
	const int32_t* threadIds, size_t size,
	int64_t initialTargetWorkDurationNanos) {
	return manager->createSession(threadIds, size, initialTargetWorkDurationNanos);
	}

	int64_t APerformanceHint_getPreferredUpdateRateNanos(APerformanceHintManager* manager) {
	return manager->getPreferredRateNanos();
	}

	int APerformanceHint_updateTargetWorkDuration(APerformanceHintSession* session,
	int64_t targetDurationNanos) {
	return session->updateTargetWorkDuration(targetDurationNanos);
	}

	int APerformanceHint_reportActualWorkDuration(APerformanceHintSession* session,
	int64_t actualDurationNanos) {
	return session->reportActualWorkDuration(actualDurationNanos);
	}

	void APerformanceHint_closeSession(APerformanceHintSession* session) {
	delete session;
	}

	int APerformanceHint_sendHint(void* session, SessionHint hint) {
	return reinterpret_cast<APerformanceHintSession*>(session)->sendHint(hint);
	}

	int APerformanceHint_setThreads(APerformanceHintSession* session, const pid_t* threadIds,
	size_t size) {
	if (session == nullptr) {
	return EINVAL;
	}
	return session->setThreads(threadIds, size);
	}

	int APerformanceHint_getThreadIds(void* aPerformanceHintSession, int32_t* const threadIds,
	size_t* const size) {
	if (aPerformanceHintSession == nullptr) {
	return EINVAL;
	}
	return static_cast<APerformanceHintSession*>(aPerformanceHintSession)
	->getThreadIds(threadIds, size);
	}

	void APerformanceHint_setIHintManagerForTesting(void* iManager) {
	delete gHintManagerForTesting;
	gHintManagerForTesting = nullptr;
	gIHintManagerForTesting = static_cast<IHintManager*>(iManager);
	}