c++ 11 多线线程系列-------- 一个最简单而且实用的线程池

至于什么是线程池，线程池是干神马的，大家自己网上查阅一下。

#include <iostream>
#include <thread>
#include <atomic>
#include <mutex>
#include <future>
#include <vector>

#include <queue>
#include <mutex>
#include <condition_variable>
#include <memory>

template<typename T>
class threadsafe_queue
{
private:
mutable std::mutex mut;
std::queue<T> data_queue;
std::condition_variable data_cond;
public:
threadsafe_queue()
{}

void push(T new_value)
{
std::lock_guard<std::mutex> lk(mut);
data_queue.push(std::move(new_value));
data_cond.notify_one();
}

void wait_and_pop(T& value)
{
std::unique_lock<std::mutex> lk(mut);
data_cond.wait(lk, [this]{return !data_queue.empty(); });
value = std::move(data_queue.front());
data_queue.pop();
}

std::shared_ptr<T> wait_and_pop()
{
std::unique_lock<std::mutex> lk(mut);
data_cond.wait(lk, [this]{return !data_queue.empty(); });
std::shared_ptr<T> res(
std::make_shared<T>(std::move(data_queue.front())));
data_queue.pop();
return res;
}

bool try_pop(T& value)
{
std::lock_guard<std::mutex> lk(mut);
if (data_queue.empty())
return false;
value = std::move(data_queue.front());
data_queue.pop();
}

std::shared_ptr<T> try_pop()
{
std::lock_guard<std::mutex> lk(mut);
if (data_queue.empty())
return std::shared_ptr<T>();
std::shared_ptr<T> res(
std::make_shared<T>(std::move(data_queue.front())));
data_queue.pop();
return res;
}

bool empty() const
{
std::lock_guard<std::mutex> lk(mut);
return data_queue.empty();
}
};

class join_threads
{
std::vector<std::thread>& threads;
public:
explicit join_threads(std::vector<std::thread>& threads_) : threads(threads_){}

~join_threads()
{
for (unsigned long i = 0; i < threads.size(); ++i)
{
if (threads[i].joinable())
threads[i].join();
}
}
};

class thread_pool
{
std::atomic<bool> done;
threadsafe_queue<std::function<void()> > work_queue;
std::vector<std::thread> threads;
join_threads joiner;

void worker_thread()
{
while (!done)
{
std::function<void()> task;
if (work_queue.try_pop(task))
{
task();
}
else
{
std::this_thread::yield();
}
}
}
public:
thread_pool() :
done(false), joiner(threads)
{
unsigned const thread_count = std::thread::hardware_concurrency();
try
{
for (unsigned i = 0; i<thread_count; ++i)
{
threads.push_back(
std::thread(&thread_pool::worker_thread, this));
}
}
catch (...)
{
done = true;
throw;
}
}

~thread_pool()
{
done = true;
}

template<typename FunctionType>
void submit(FunctionType f)
{
work_queue.push(std::function<void()>(f));
}
};