typesense/include/threadpool.h

107 lines
3.1 KiB
C++

// https://github.com/jhasse/ThreadPool
#pragma once
#include <functional>
#include <future>
#include <queue>
#include "logger.h"
class ThreadPool {
public:
explicit ThreadPool(size_t);
template<class F, class... Args>
decltype(auto) enqueue(F&& f, Args&&... args);
void log_exhaustion();
void shutdown();
private:
// need to keep track of threads so we can join them
std::vector< std::thread > workers;
// the task queue
std::queue< std::packaged_task<void()> > tasks;
// synchronization
std::mutex queue_mutex;
std::condition_variable condition;
std::condition_variable condition_producers;
bool stop;
};
// the constructor just launches some amount of workers
inline ThreadPool::ThreadPool(size_t threads)
: stop(false)
{
for(size_t i = 0;i<threads;++i)
workers.emplace_back(
[this]
{
for(;;)
{
std::packaged_task<void()> task;
{
std::unique_lock<std::mutex> lock(this->queue_mutex);
this->condition.wait(lock,
[this]{ return this->stop || !this->tasks.empty(); });
if(this->stop) {
return;
}
if(this->tasks.empty()) {
continue;
}
task = std::move(this->tasks.front());
this->tasks.pop();
if (tasks.empty()) {
condition_producers.notify_one(); // notify the destructor that the queue is empty
}
}
task();
}
}
);
}
// add new work item to the pool
template<class F, class... Args>
decltype(auto) ThreadPool::enqueue(F&& f, Args&&... args)
{
using return_type = std::invoke_result_t<F, Args...>;
std::packaged_task<return_type()> task(
std::bind(std::forward<F>(f), std::forward<Args>(args)...)
);
std::future<return_type> res = task.get_future();
{
std::unique_lock<std::mutex> lock(queue_mutex);
// don't allow enqueueing after stopping the pool
if(!stop) {
tasks.emplace(std::move(task));
}
}
condition.notify_one();
return res;
}
inline void ThreadPool::shutdown() {
{
std::unique_lock<std::mutex> lock(queue_mutex);
condition_producers.wait(lock, [this] { return tasks.empty(); });
stop = true;
}
condition.notify_all();
for (std::thread& worker : workers) {
worker.join();
}
}
inline void ThreadPool::log_exhaustion() {
std::unique_lock<std::mutex> lock(queue_mutex);
if(tasks.size() >= workers.size()) {
LOG(WARNING) << "Threadpool exhaustion detected, task_queue_len: "
<< tasks.size() << ", thread_pool_len: " << workers.size();
}
}