base/threading/worker_pool_posix.cc

// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/threading/worker_pool_posix.h"

#include "base/bind.h"
#include "base/callback.h"
#include "base/lazy_instance.h"
#include "base/logging.h"
#include "base/memory/ref_counted.h"
#include "base/strings/stringprintf.h"
#include "base/threading/platform_thread.h"
#include "base/threading/thread_local.h"
#include "base/threading/worker_pool.h"
#include "base/trace_event/trace_event.h"
#include "base/tracked_objects.h"

using tracked_objects::TrackedTime;

namespace base {

namespace {

LazyInstance<ThreadLocalBoolean>::Leaky g_worker_pool_running_on_this_thread =
    LAZY_INSTANCE_INITIALIZER;

const int64 kIdleSecondsBeforeExit = 10 * 60;

class WorkerPoolImpl {
 public:
  WorkerPoolImpl();
  ~WorkerPoolImpl();

  void PostTask(const tracked_objects::Location& from_here,
                const Closure& task,
                bool task_is_slow);

  void ShutDownCleanly();

 private:
  scoped_refptr<PosixDynamicThreadPool> pool_;
};

WorkerPoolImpl::WorkerPoolImpl()
    : pool_(new PosixDynamicThreadPool(
          "WorkerPool",
          TimeDelta::FromSeconds(kIdleSecondsBeforeExit))) {
}

WorkerPoolImpl::~WorkerPoolImpl() {
  pool_->Terminate(false);
}

void WorkerPoolImpl::PostTask(const tracked_objects::Location& from_here,
                              const Closure& task,
                              bool task_is_slow) {
  pool_->PostTask(from_here, task);
}

void WorkerPoolImpl::ShutDownCleanly() {
  pool_->Terminate(true);
}

LazyInstance<WorkerPoolImpl> g_lazy_worker_pool = LAZY_INSTANCE_INITIALIZER;

class WorkerThread : public PlatformThread::Delegate {
 public:
  WorkerThread(const std::string& name_prefix, PosixDynamicThreadPool* pool)
      : name_prefix_(name_prefix), pool_(pool) {}

  void ThreadMain() override;

 private:
  const std::string name_prefix_;
  scoped_refptr<PosixDynamicThreadPool> pool_;

  DISALLOW_COPY_AND_ASSIGN(WorkerThread);
};

void WorkerThread::ThreadMain() {
  g_worker_pool_running_on_this_thread.Get().Set(true);
  const std::string name =
      StringPrintf("%s/%d", name_prefix_.c_str(), PlatformThread::CurrentId());
  // Note |name.c_str()| must remain valid for for the whole life of the thread.
  PlatformThread::SetName(name);

  for (;;) {
    PendingTask pending_task = pool_->WaitForTask();
    if (pending_task.task.is_null())
      break;
    TRACE_EVENT2("toplevel", "WorkerThread::ThreadMain::Run",
        "src_file", pending_task.posted_from.file_name(),
        "src_func", pending_task.posted_from.function_name());

    tracked_objects::TaskStopwatch stopwatch;
    stopwatch.Start();
    pending_task.task.Run();
    stopwatch.Stop();

    tracked_objects::ThreadData::TallyRunOnWorkerThreadIfTracking(
        pending_task.birth_tally, pending_task.time_posted, stopwatch);
  }

  pool_->NotifyWorkerIsGoingAway(PlatformThread::CurrentHandle());
  delete this;
}

}  // namespace

// static
bool WorkerPool::PostTask(const tracked_objects::Location& from_here,
                          const Closure& task,
                          bool task_is_slow) {
  g_lazy_worker_pool.Pointer()->PostTask(from_here, task, task_is_slow);
  return true;
}

// static
bool WorkerPool::RunsTasksOnCurrentThread() {
  return g_worker_pool_running_on_this_thread.Get().Get();
}

// static
void WorkerPool::ShutDownCleanly() {
  g_lazy_worker_pool.Pointer()->ShutDownCleanly();
}

PosixDynamicThreadPool::PosixDynamicThreadPool(const std::string& name_prefix,
                                               TimeDelta idle_time_before_exit)
    : name_prefix_(name_prefix),
      idle_time_before_exit_(idle_time_before_exit),
      pending_tasks_available_cv_(&lock_),
      num_idle_threads_(0),
      has_pending_cleanup_task_(false),
      terminated_(false) {
}

PosixDynamicThreadPool::~PosixDynamicThreadPool() {
  while (!pending_tasks_.empty())
    pending_tasks_.pop();
}

void PosixDynamicThreadPool::Terminate(bool blocking) {
  std::vector<PlatformThreadHandle> threads_to_cleanup;
  std::vector<PlatformThreadHandle> worker_threads;
  {
    AutoLock locked(lock_);
    if (terminated_)
      return;
    terminated_ = true;

    threads_to_cleanup.swap(threads_to_cleanup_);
    worker_threads.swap(worker_threads_);
  }
  pending_tasks_available_cv_.Broadcast();

  if (blocking) {
    for (const auto& item : threads_to_cleanup)
      PlatformThread::Join(item);

    for (const auto& item : worker_threads)
      PlatformThread::Join(item);

    // No need to take the lock. No one else should be accessing these members.
    DCHECK_EQ(0u, num_idle_threads_);
    // The following members should not have new elements added after
    // |terminated_| is set to true.
    DCHECK(threads_to_cleanup_.empty());
    DCHECK(worker_threads_.empty());
  }
}

void PosixDynamicThreadPool::PostTask(
    const tracked_objects::Location& from_here,
    const Closure& task) {
  PendingTask pending_task(from_here, task);
  AutoLock locked(lock_);
  AddTaskNoLock(&pending_task);
}

PendingTask PosixDynamicThreadPool::WaitForTask() {
  AutoLock locked(lock_);

  if (terminated_)
    return PendingTask(FROM_HERE, Closure());

  if (pending_tasks_.empty()) {  // No work available, wait for work.
    num_idle_threads_++;
    if (num_threads_cv_)
      num_threads_cv_->Broadcast();
    pending_tasks_available_cv_.TimedWait(idle_time_before_exit_);
    num_idle_threads_--;
    if (num_threads_cv_)
      num_threads_cv_->Broadcast();
    if (pending_tasks_.empty()) {
      // We waited for work, but there's still no work.  Return an empty task to
      // signal the thread to terminate.
      return PendingTask(FROM_HERE, Closure());
    }
  }

  PendingTask pending_task = pending_tasks_.front();
  pending_tasks_.pop();
  return pending_task;
}

void PosixDynamicThreadPool::NotifyWorkerIsGoingAway(
    PlatformThreadHandle worker) {
  AutoLock locked(lock_);
  if (terminated_)
    return;

  auto new_end = std::remove_if(worker_threads_.begin(), worker_threads_.end(),
                                [worker](PlatformThreadHandle handle) {
                                  return handle.is_equal(worker);
                                });
  DCHECK_EQ(1, worker_threads_.end() - new_end);
  worker_threads_.erase(new_end, worker_threads_.end());

  threads_to_cleanup_.push_back(worker);

  if (num_threads_cv_)
    num_threads_cv_->Broadcast();

  if (!has_pending_cleanup_task_) {
    has_pending_cleanup_task_ = true;
    PendingTask pending_task(
        FROM_HERE,
        base::Bind(&PosixDynamicThreadPool::CleanUpThreads, Unretained(this)));
    AddTaskNoLock(&pending_task);
  }
}

void PosixDynamicThreadPool::AddTaskNoLock(PendingTask* pending_task) {
  lock_.AssertAcquired();

  if (terminated_) {
    LOG(WARNING)
        << "This thread pool is already terminated.  Do not post new tasks.";
    return;
  }

  pending_tasks_.push(*pending_task);
  pending_task->task.Reset();

  // We have enough worker threads.
  if (num_idle_threads_ >=
      pending_tasks_.size() - (has_pending_cleanup_task_ ? 1 : 0)) {
    pending_tasks_available_cv_.Signal();
  } else {
    // The new PlatformThread will take ownership of the WorkerThread object,
    // which will delete itself on exit.
    WorkerThread* worker = new WorkerThread(name_prefix_, this);
    PlatformThreadHandle handle;
    PlatformThread::Create(0, worker, &handle);
    worker_threads_.push_back(handle);

    if (num_threads_cv_)
      num_threads_cv_->Broadcast();
  }
}

void PosixDynamicThreadPool::CleanUpThreads() {
  std::vector<PlatformThreadHandle> threads_to_cleanup;
  {
    AutoLock locked(lock_);
    DCHECK(has_pending_cleanup_task_);
    has_pending_cleanup_task_ = false;
    threads_to_cleanup.swap(threads_to_cleanup_);
  }
  for (const auto& item : threads_to_cleanup)
    PlatformThread::Join(item);
}

}  // namespace base