base/task/thread_pool/thread_pool_instance.cc

// Copyright 2016 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/task/thread_pool/thread_pool_instance.h"

#include <algorithm>

#include "base/logging.h"
#include "base/memory/ptr_util.h"
#include "base/system/sys_info.h"
#include "base/task/thread_pool/thread_pool_impl.h"
#include "base/threading/platform_thread.h"
#include "base/time/time.h"

namespace base {

namespace {

// |g_thread_pool| is intentionally leaked on shutdown.
ThreadPoolInstance* g_thread_pool = nullptr;

}  // namespace

ThreadPoolInstance::InitParams::InitParams(int max_num_foreground_threads_in)
    : max_num_foreground_threads(max_num_foreground_threads_in) {}

ThreadPoolInstance::InitParams::~InitParams() = default;

ThreadPoolInstance::ScopedExecutionFence::ScopedExecutionFence() {
  DCHECK(g_thread_pool);
  g_thread_pool->SetHasFence(true);
}

ThreadPoolInstance::ScopedExecutionFence::~ScopedExecutionFence() {
  DCHECK(g_thread_pool);
  g_thread_pool->SetHasFence(false);
}

ThreadPoolInstance::ScopedBestEffortExecutionFence::
    ScopedBestEffortExecutionFence() {
  DCHECK(g_thread_pool);
  g_thread_pool->SetHasBestEffortFence(true);
}

ThreadPoolInstance::ScopedBestEffortExecutionFence::
    ~ScopedBestEffortExecutionFence() {
  DCHECK(g_thread_pool);
  g_thread_pool->SetHasBestEffortFence(false);
}

#if !defined(OS_NACL)
// static
void ThreadPoolInstance::CreateAndStartWithDefaultParams(StringPiece name) {
  Create(name);
  g_thread_pool->StartWithDefaultParams();
}

void ThreadPoolInstance::StartWithDefaultParams() {
  // Values were chosen so that:
  // * There are few background threads.
  // * Background threads never outnumber foreground threads.
  // * The system is utilized maximally by foreground threads.
  // * The main thread is assumed to be busy, cap foreground workers at
  //   |num_cores - 1|.
  const int num_cores = SysInfo::NumberOfProcessors();
  const int max_num_foreground_threads = std::max(3, num_cores - 1);
  Start({max_num_foreground_threads});
}
#endif  // !defined(OS_NACL)

void ThreadPoolInstance::Create(StringPiece name) {
  Set(std::make_unique<internal::ThreadPoolImpl>(name));
}

// static
void ThreadPoolInstance::Set(std::unique_ptr<ThreadPoolInstance> thread_pool) {
  delete g_thread_pool;
  g_thread_pool = thread_pool.release();
}

// static
ThreadPoolInstance* ThreadPoolInstance::Get() {
  return g_thread_pool;
}

}  // namespace base