blob: e59ddcc0676a8cb9818114ff7ee57ffdab6ccdc1 [file] [log] [blame]
// Copyright 2018 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 "worker_pool.h"
#include "base/command_line.h"
#include "base/strings/string_number_conversions.h"
#include "sys_info.h"
#include "tools/gn/switches.h"
namespace {
int GetThreadCount() {
std::string thread_count =
base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
switches::kThreads);
// See if an override was specified on the command line.
int result;
if (!thread_count.empty() && base::StringToInt(thread_count, &result) &&
result >= 1) {
return result;
}
// Base the default number of worker threads on number of cores in the
// system. When building large projects, the speed can be limited by how fast
// the main thread can dispatch work and connect the dependency graph. If
// there are too many worker threads, the main thread can be starved and it
// will run slower overall.
//
// One less worker thread than the number of physical CPUs seems to be a
// good value, both theoretically and experimentally. But always use at
// least some workers to prevent us from being too sensitive to I/O latency
// on low-end systems.
//
// The minimum thread count is based on measuring the optimal threads for the
// Chrome build on a several-year-old 4-core MacBook.
// Almost all CPUs now are hyperthreaded.
int num_cores = NumberOfProcessors() / 2;
return std::max(num_cores - 1, 8);
}
} // namespace
WorkerPool::WorkerPool() : WorkerPool(GetThreadCount()) {}
WorkerPool::WorkerPool(size_t thread_count)
: should_stop_processing_(false) {
threads_.reserve(thread_count);
for (size_t i = 0; i < thread_count; ++i)
threads_.emplace_back([this]() { Worker(); });
}
WorkerPool::~WorkerPool() {
{
std::unique_lock<std::mutex> queue_lock(queue_mutex_);
should_stop_processing_ = true;
}
pool_notifier_.notify_all();
for (auto& task_thread : threads_) {
task_thread.join();
}
}
void WorkerPool::PostTask(Task work) {
{
std::unique_lock<std::mutex> queue_lock(queue_mutex_);
CHECK(!should_stop_processing_);
task_queue_.emplace(std::move(work));
}
pool_notifier_.notify_one();
}
void WorkerPool::Worker() {
for (;;) {
Task task;
{
std::unique_lock<std::mutex> queue_lock(queue_mutex_);
pool_notifier_.wait(queue_lock, [this]() {
return (!task_queue_.empty()) || should_stop_processing_;
});
if (should_stop_processing_ && task_queue_.empty())
return;
task = std::move(task_queue_.front());
task_queue_.pop();
}
std::move(task).Run();
}
}