ClickHouse/dbms/include/DB/Common/ThreadPool.h
2016-08-13 08:29:53 +03:00

62 lines
1.7 KiB
C++

#pragma once
#include <cstdint>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <functional>
#include <queue>
#include <vector>
/** Very simple thread pool similar to boost::threadpool.
* Advantages:
* - catches exceptions and rethrows on wait.
*/
class ThreadPool
{
private:
using Job = std::function<void()>;
public:
/// Size is constant, all threads are created immediately.
ThreadPool(size_t m_size);
/// Add new job. Locks until free thread in pool become available or exception in one of threads was thrown.
/// If an exception in some thread was thrown, method silently returns, and exception will be rethrown only on call to 'wait' function.
void schedule(Job job);
/// Wait for all currently active jobs to be done.
/// You may call schedule and wait many times in arbitary order.
/// If any thread was throw an exception, it will be rethrown from this method.
/// List of exceptions is not cleared: on subsequent calls to wait, same exception will be rethrown.
void wait();
/// Waits for all threads. Doesn't rethrow exceptions (use 'wait' method to rethrow exceptions).
/// You should not destroy object while calling schedule or wait methods from another threads.
~ThreadPool();
size_t size() const { return m_size; }
/// Returns number of active jobs.
size_t active() const;
private:
mutable std::mutex mutex;
std::condition_variable has_free_thread;
std::condition_variable has_new_job_or_shutdown;
const size_t m_size;
size_t active_jobs = 0;
bool shutdown = false;
std::queue<Job> jobs;
std::vector<std::thread> threads;
std::vector<std::exception_ptr> exceptions; /// NOTE Saving many exceptions but we rethrow just first one.
void worker();
};