runtime/thread_pool.cc - platform/art - Gitiles

 /*
  * Copyright (C) 2012 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.
  */

 #include "thread_pool.h"

 #include "base/casts.h"
 #include "base/stl_util.h"
 #include "runtime.h"
 #include "thread-inl.h"

 namespace art {

 static constexpr bool kMeasureWaitTime = false;

 ThreadPoolWorker::ThreadPoolWorker(ThreadPool* thread_pool, const std::string& name,
                                    size_t stack_size)
     : thread_pool_(thread_pool),
       name_(name) {
   std::string error_msg;
   stack_.reset(MemMap::MapAnonymous(name.c_str(), nullptr, stack_size, PROT_READ | PROT_WRITE,
                                     false, &error_msg));
   CHECK(stack_.get() != nullptr) << error_msg;
   const char* reason = "new thread pool worker thread";
   pthread_attr_t attr;
   CHECK_PTHREAD_CALL(pthread_attr_init, (&attr), reason);
   CHECK_PTHREAD_CALL(pthread_attr_setstack, (&attr, stack_->Begin(), stack_->Size()), reason);
   CHECK_PTHREAD_CALL(pthread_create, (&pthread_, &attr, &Callback, this), reason);
   CHECK_PTHREAD_CALL(pthread_attr_destroy, (&attr), reason);
 }

 ThreadPoolWorker::~ThreadPoolWorker() {
   CHECK_PTHREAD_CALL(pthread_join, (pthread_, nullptr), "thread pool worker shutdown");
 }

 void ThreadPoolWorker::Run() {
   Thread* self = Thread::Current();
   Task* task = nullptr;
   thread_pool_->creation_barier_.Wait(self);
   while ((task = thread_pool_->GetTask(self)) != nullptr) {
     task->Run(self);
     task->Finalize();
   }
 }

 void* ThreadPoolWorker::Callback(void* arg) {
   ThreadPoolWorker* worker = reinterpret_cast<ThreadPoolWorker*>(arg);
   Runtime* runtime = Runtime::Current();
   CHECK(runtime->AttachCurrentThread(worker->name_.c_str(), true, nullptr, false));
   // Do work until its time to shut down.
   worker->Run();
   runtime->DetachCurrentThread();
   return nullptr;
 }

 void ThreadPool::AddTask(Thread* self, Task* task) {
   MutexLock mu(self, task_queue_lock_);
   tasks_.push_back(task);
   // If we have any waiters, signal one.
   if (started_ && waiting_count_ != 0) {
     task_queue_condition_.Signal(self);
   }
 }

 ThreadPool::ThreadPool(const char* name, size_t num_threads)
   : name_(name),
     task_queue_lock_("task queue lock"),
     task_queue_condition_("task queue condition", task_queue_lock_),
     completion_condition_("task completion condition", task_queue_lock_),
     started_(false),
     shutting_down_(false),
     waiting_count_(0),
     start_time_(0),
     total_wait_time_(0),
     // Add one since the caller of constructor waits on the barrier too.
     creation_barier_(num_threads + 1),
     max_active_workers_(num_threads) {
   Thread* self = Thread::Current();
   while (GetThreadCount() < num_threads) {
     const std::string worker_name = StringPrintf("%s worker thread %zu", name_.c_str(),
                                                  GetThreadCount());
     threads_.push_back(new ThreadPoolWorker(this, worker_name, ThreadPoolWorker::kDefaultStackSize));
   }
   // Wait for all of the threads to attach.
   creation_barier_.Wait(self);
 }

 void ThreadPool::SetMaxActiveWorkers(size_t threads) {
   MutexLock mu(Thread::Current(), task_queue_lock_);
   CHECK_LE(threads, GetThreadCount());
   max_active_workers_ = threads;
 }

 ThreadPool::~ThreadPool() {
   {
     Thread* self = Thread::Current();
     MutexLock mu(self, task_queue_lock_);
     // Tell any remaining workers to shut down.
     shutting_down_ = true;
     // Broadcast to everyone waiting.
     task_queue_condition_.Broadcast(self);
     completion_condition_.Broadcast(self);
   }
   // Wait for the threads to finish.
   STLDeleteElements(&threads_);
 }

 void ThreadPool::StartWorkers(Thread* self) {
   MutexLock mu(self, task_queue_lock_);
   started_ = true;
   task_queue_condition_.Broadcast(self);
   start_time_ = NanoTime();
   total_wait_time_ = 0;
 }

 void ThreadPool::StopWorkers(Thread* self) {
   MutexLock mu(self, task_queue_lock_);
   started_ = false;
 }

 Task* ThreadPool::GetTask(Thread* self) {
   MutexLock mu(self, task_queue_lock_);
   while (!IsShuttingDown()) {
     const size_t thread_count = GetThreadCount();
     // Ensure that we don't use more threads than the maximum active workers.
     const size_t active_threads = thread_count - waiting_count_;
     // <= since self is considered an active worker.
     if (active_threads <= max_active_workers_) {
       Task* task = TryGetTaskLocked();
       if (task != nullptr) {
         return task;
       }
     }

     ++waiting_count_;
     if (waiting_count_ == GetThreadCount() && tasks_.empty()) {
       // We may be done, lets broadcast to the completion condition.
       completion_condition_.Broadcast(self);
     }
     const uint64_t wait_start = kMeasureWaitTime ? NanoTime() : 0;
     task_queue_condition_.Wait(self);
     if (kMeasureWaitTime) {
       const uint64_t wait_end = NanoTime();
       total_wait_time_ += wait_end - std::max(wait_start, start_time_);
     }
     --waiting_count_;
   }

   // We are shutting down, return nullptr to tell the worker thread to stop looping.
   return nullptr;
 }

 Task* ThreadPool::TryGetTask(Thread* self) {
   MutexLock mu(self, task_queue_lock_);
   return TryGetTaskLocked();
 }

 Task* ThreadPool::TryGetTaskLocked() {
   if (started_ && !tasks_.empty()) {
     Task* task = tasks_.front();
     tasks_.pop_front();
     return task;
   }
   return nullptr;
 }

 void ThreadPool::Wait(Thread* self, bool do_work, bool may_hold_locks) {
   if (do_work) {
     Task* task = nullptr;
     while ((task = TryGetTask(self)) != nullptr) {
       task->Run(self);
       task->Finalize();
     }
   }
   // Wait until each thread is waiting and the task list is empty.
   MutexLock mu(self, task_queue_lock_);
   while (!shutting_down_ && (waiting_count_ != GetThreadCount() || !tasks_.empty())) {
     if (!may_hold_locks) {
       completion_condition_.Wait(self);
     } else {
       completion_condition_.WaitHoldingLocks(self);
     }
   }
 }

 size_t ThreadPool::GetTaskCount(Thread* self) {
   MutexLock mu(self, task_queue_lock_);
   return tasks_.size();
 }

 WorkStealingWorker::WorkStealingWorker(ThreadPool* thread_pool, const std::string& name,
                                        size_t stack_size)
     : ThreadPoolWorker(thread_pool, name, stack_size), task_(nullptr) {}

 void WorkStealingWorker::Run() {
   Thread* self = Thread::Current();
   Task* task = nullptr;
   WorkStealingThreadPool* thread_pool = down_cast<WorkStealingThreadPool*>(thread_pool_);
   while ((task = thread_pool_->GetTask(self)) != nullptr) {
     WorkStealingTask* stealing_task = down_cast<WorkStealingTask*>(task);

     {
       CHECK(task_ == nullptr);
       MutexLock mu(self, thread_pool->work_steal_lock_);
       // Register that we are running the task
       ++stealing_task->ref_count_;
       task_ = stealing_task;
     }
     stealing_task->Run(self);
     // Mark ourselves as not running a task so that nobody tries to steal from us.
     // There is a race condition that someone starts stealing from us at this point. This is okay
     // due to the reference counting.
     task_ = nullptr;

     bool finalize;

     // Steal work from tasks until there is none left to steal. Note: There is a race, but
     // all that happens when the race occurs is that we steal some work instead of processing a
     // task from the queue.
     while (thread_pool->GetTaskCount(self) == 0) {
       WorkStealingTask* steal_from_task  = nullptr;

       {
         MutexLock mu(self, thread_pool->work_steal_lock_);
         // Try finding a task to steal from.
         steal_from_task = thread_pool->FindTaskToStealFrom();
         if (steal_from_task != nullptr) {
           CHECK_NE(stealing_task, steal_from_task)
               << "Attempting to steal from completed self task";
           steal_from_task->ref_count_++;
         } else {
           break;
         }
       }

       if (steal_from_task != nullptr) {
         // Task which completed earlier is going to steal some work.
         stealing_task->StealFrom(self, steal_from_task);

         {
           // We are done stealing from the task, lets decrement its reference count.
           MutexLock mu(self, thread_pool->work_steal_lock_);
           finalize = !--steal_from_task->ref_count_;
         }

         if (finalize) {
           steal_from_task->Finalize();
         }
       }
     }

     {
       MutexLock mu(self, thread_pool->work_steal_lock_);
       // If nobody is still referencing task_ we can finalize it.
       finalize = !--stealing_task->ref_count_;
     }

     if (finalize) {
       stealing_task->Finalize();
     }
   }
 }

 WorkStealingWorker::~WorkStealingWorker() {}

 WorkStealingThreadPool::WorkStealingThreadPool(const char* name, size_t num_threads)
     : ThreadPool(name, 0),
       work_steal_lock_("work stealing lock"),
       steal_index_(0) {
   while (GetThreadCount() < num_threads) {
     const std::string worker_name = StringPrintf("Work stealing worker %zu", GetThreadCount());
     threads_.push_back(new WorkStealingWorker(this, worker_name,
                                               ThreadPoolWorker::kDefaultStackSize));
   }
 }

 WorkStealingTask* WorkStealingThreadPool::FindTaskToStealFrom() {
   const size_t thread_count = GetThreadCount();
   for (size_t i = 0; i < thread_count; ++i) {
     // TODO: Use CAS instead of lock.
     ++steal_index_;
     if (steal_index_ >= thread_count) {
       steal_index_-= thread_count;
     }

     WorkStealingWorker* worker = down_cast<WorkStealingWorker*>(threads_[steal_index_]);
     WorkStealingTask* task = worker->task_;
     if (task) {
       // Not null, we can probably steal from this worker.
       return task;
     }
   }
   // Couldn't find something to steal.
   return nullptr;
 }

 WorkStealingThreadPool::~WorkStealingThreadPool() {}

 }  // namespace art
	/*
	* Copyright (C) 2012 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.
	*/

	#include "thread_pool.h"

	#include "base/casts.h"
	#include "base/stl_util.h"
	#include "runtime.h"
	#include "thread-inl.h"

	namespace art {

	static constexpr bool kMeasureWaitTime = false;

	ThreadPoolWorker::ThreadPoolWorker(ThreadPool* thread_pool, const std::string& name,
	size_t stack_size)
	: thread_pool_(thread_pool),
	name_(name) {
	std::string error_msg;
	stack_.reset(MemMap::MapAnonymous(name.c_str(), nullptr, stack_size, PROT_READ \| PROT_WRITE,
	false, &error_msg));
	CHECK(stack_.get() != nullptr) << error_msg;
	const char* reason = "new thread pool worker thread";
	pthread_attr_t attr;
	CHECK_PTHREAD_CALL(pthread_attr_init, (&attr), reason);
	CHECK_PTHREAD_CALL(pthread_attr_setstack, (&attr, stack_->Begin(), stack_->Size()), reason);
	CHECK_PTHREAD_CALL(pthread_create, (&pthread_, &attr, &Callback, this), reason);
	CHECK_PTHREAD_CALL(pthread_attr_destroy, (&attr), reason);
	}

	ThreadPoolWorker::~ThreadPoolWorker() {
	CHECK_PTHREAD_CALL(pthread_join, (pthread_, nullptr), "thread pool worker shutdown");
	}

	void ThreadPoolWorker::Run() {
	Thread* self = Thread::Current();
	Task* task = nullptr;
	thread_pool_->creation_barier_.Wait(self);
	while ((task = thread_pool_->GetTask(self)) != nullptr) {
	task->Run(self);
	task->Finalize();
	}
	}

	void* ThreadPoolWorker::Callback(void* arg) {
	ThreadPoolWorker* worker = reinterpret_cast<ThreadPoolWorker*>(arg);
	Runtime* runtime = Runtime::Current();
	CHECK(runtime->AttachCurrentThread(worker->name_.c_str(), true, nullptr, false));
	// Do work until its time to shut down.
	worker->Run();
	runtime->DetachCurrentThread();
	return nullptr;
	}

	void ThreadPool::AddTask(Thread* self, Task* task) {
	MutexLock mu(self, task_queue_lock_);
	tasks_.push_back(task);
	// If we have any waiters, signal one.
	if (started_ && waiting_count_ != 0) {
	task_queue_condition_.Signal(self);
	}
	}

	ThreadPool::ThreadPool(const char* name, size_t num_threads)
	: name_(name),
	task_queue_lock_("task queue lock"),
	task_queue_condition_("task queue condition", task_queue_lock_),
	completion_condition_("task completion condition", task_queue_lock_),
	started_(false),
	shutting_down_(false),
	waiting_count_(0),
	start_time_(0),
	total_wait_time_(0),
	// Add one since the caller of constructor waits on the barrier too.
	creation_barier_(num_threads + 1),
	max_active_workers_(num_threads) {
	Thread* self = Thread::Current();
	while (GetThreadCount() < num_threads) {
	const std::string worker_name = StringPrintf("%s worker thread %zu", name_.c_str(),
	GetThreadCount());
	threads_.push_back(new ThreadPoolWorker(this, worker_name, ThreadPoolWorker::kDefaultStackSize));
	}
	// Wait for all of the threads to attach.
	creation_barier_.Wait(self);
	}

	void ThreadPool::SetMaxActiveWorkers(size_t threads) {
	MutexLock mu(Thread::Current(), task_queue_lock_);
	CHECK_LE(threads, GetThreadCount());
	max_active_workers_ = threads;
	}

	ThreadPool::~ThreadPool() {
	{
	Thread* self = Thread::Current();
	MutexLock mu(self, task_queue_lock_);
	// Tell any remaining workers to shut down.
	shutting_down_ = true;
	// Broadcast to everyone waiting.
	task_queue_condition_.Broadcast(self);
	completion_condition_.Broadcast(self);
	}
	// Wait for the threads to finish.
	STLDeleteElements(&threads_);
	}

	void ThreadPool::StartWorkers(Thread* self) {
	MutexLock mu(self, task_queue_lock_);
	started_ = true;
	task_queue_condition_.Broadcast(self);
	start_time_ = NanoTime();
	total_wait_time_ = 0;
	}

	void ThreadPool::StopWorkers(Thread* self) {
	MutexLock mu(self, task_queue_lock_);
	started_ = false;
	}

	Task* ThreadPool::GetTask(Thread* self) {
	MutexLock mu(self, task_queue_lock_);
	while (!IsShuttingDown()) {
	const size_t thread_count = GetThreadCount();
	// Ensure that we don't use more threads than the maximum active workers.
	const size_t active_threads = thread_count - waiting_count_;
	// <= since self is considered an active worker.
	if (active_threads <= max_active_workers_) {
	Task* task = TryGetTaskLocked();
	if (task != nullptr) {
	return task;
	}
	}

	++waiting_count_;
	if (waiting_count_ == GetThreadCount() && tasks_.empty()) {
	// We may be done, lets broadcast to the completion condition.
	completion_condition_.Broadcast(self);
	}
	const uint64_t wait_start = kMeasureWaitTime ? NanoTime() : 0;
	task_queue_condition_.Wait(self);
	if (kMeasureWaitTime) {
	const uint64_t wait_end = NanoTime();
	total_wait_time_ += wait_end - std::max(wait_start, start_time_);
	}
	--waiting_count_;
	}

	// We are shutting down, return nullptr to tell the worker thread to stop looping.
	return nullptr;
	}

	Task* ThreadPool::TryGetTask(Thread* self) {
	MutexLock mu(self, task_queue_lock_);
	return TryGetTaskLocked();
	}

	Task* ThreadPool::TryGetTaskLocked() {
	if (started_ && !tasks_.empty()) {
	Task* task = tasks_.front();
	tasks_.pop_front();
	return task;
	}
	return nullptr;
	}

	void ThreadPool::Wait(Thread* self, bool do_work, bool may_hold_locks) {
	if (do_work) {
	Task* task = nullptr;
	while ((task = TryGetTask(self)) != nullptr) {
	task->Run(self);
	task->Finalize();
	}
	}
	// Wait until each thread is waiting and the task list is empty.
	MutexLock mu(self, task_queue_lock_);
	while (!shutting_down_ && (waiting_count_ != GetThreadCount() \|\| !tasks_.empty())) {
	if (!may_hold_locks) {
	completion_condition_.Wait(self);
	} else {
	completion_condition_.WaitHoldingLocks(self);
	}
	}
	}

	size_t ThreadPool::GetTaskCount(Thread* self) {
	MutexLock mu(self, task_queue_lock_);
	return tasks_.size();
	}

	WorkStealingWorker::WorkStealingWorker(ThreadPool* thread_pool, const std::string& name,
	size_t stack_size)
	: ThreadPoolWorker(thread_pool, name, stack_size), task_(nullptr) {}

	void WorkStealingWorker::Run() {
	Thread* self = Thread::Current();
	Task* task = nullptr;
	WorkStealingThreadPool* thread_pool = down_cast<WorkStealingThreadPool*>(thread_pool_);
	while ((task = thread_pool_->GetTask(self)) != nullptr) {
	WorkStealingTask* stealing_task = down_cast<WorkStealingTask*>(task);

	{
	CHECK(task_ == nullptr);
	MutexLock mu(self, thread_pool->work_steal_lock_);
	// Register that we are running the task
	++stealing_task->ref_count_;
	task_ = stealing_task;
	}
	stealing_task->Run(self);
	// Mark ourselves as not running a task so that nobody tries to steal from us.
	// There is a race condition that someone starts stealing from us at this point. This is okay
	// due to the reference counting.
	task_ = nullptr;

	bool finalize;

	// Steal work from tasks until there is none left to steal. Note: There is a race, but
	// all that happens when the race occurs is that we steal some work instead of processing a
	// task from the queue.
	while (thread_pool->GetTaskCount(self) == 0) {
	WorkStealingTask* steal_from_task = nullptr;

	{
	MutexLock mu(self, thread_pool->work_steal_lock_);
	// Try finding a task to steal from.
	steal_from_task = thread_pool->FindTaskToStealFrom();
	if (steal_from_task != nullptr) {
	CHECK_NE(stealing_task, steal_from_task)
	<< "Attempting to steal from completed self task";
	steal_from_task->ref_count_++;
	} else {
	break;
	}
	}

	if (steal_from_task != nullptr) {
	// Task which completed earlier is going to steal some work.
	stealing_task->StealFrom(self, steal_from_task);

	{
	// We are done stealing from the task, lets decrement its reference count.
	MutexLock mu(self, thread_pool->work_steal_lock_);
	finalize = !--steal_from_task->ref_count_;
	}

	if (finalize) {
	steal_from_task->Finalize();
	}
	}
	}

	{
	MutexLock mu(self, thread_pool->work_steal_lock_);
	// If nobody is still referencing task_ we can finalize it.
	finalize = !--stealing_task->ref_count_;
	}

	if (finalize) {
	stealing_task->Finalize();
	}
	}
	}

	WorkStealingWorker::~WorkStealingWorker() {}

	WorkStealingThreadPool::WorkStealingThreadPool(const char* name, size_t num_threads)
	: ThreadPool(name, 0),
	work_steal_lock_("work stealing lock"),
	steal_index_(0) {
	while (GetThreadCount() < num_threads) {
	const std::string worker_name = StringPrintf("Work stealing worker %zu", GetThreadCount());
	threads_.push_back(new WorkStealingWorker(this, worker_name,
	ThreadPoolWorker::kDefaultStackSize));
	}
	}

	WorkStealingTask* WorkStealingThreadPool::FindTaskToStealFrom() {
	const size_t thread_count = GetThreadCount();
	for (size_t i = 0; i < thread_count; ++i) {
	// TODO: Use CAS instead of lock.
	++steal_index_;
	if (steal_index_ >= thread_count) {
	steal_index_-= thread_count;
	}

	WorkStealingWorker* worker = down_cast<WorkStealingWorker*>(threads_[steal_index_]);
	WorkStealingTask* task = worker->task_;
	if (task) {
	// Not null, we can probably steal from this worker.
	return task;
	}
	}
	// Couldn't find something to steal.
	return nullptr;
	}

	WorkStealingThreadPool::~WorkStealingThreadPool() {}

	} // namespace art