In this post, I will introduce how to build a simple thread pool in C++. <\/p>\n
The codes are from here<\/a>. The thread pool only uses I add some comments in the original codes. Please be compliant with the original license in the post<\/a>. An improved version is available here<\/a>.<\/p>\n I present some related techniques. <\/p>\nthread<\/code>, mutex<\/code>, and condition_variable<\/code>. <\/p>\n#include <thread>\n#include <mutex>\n#include <condition_variable>\n\nclass ThreadPool;\n\n\/\/ our worker thread objects\nclass Worker {\npublic:\n Worker(ThreadPool &s) : pool(s) { }\n void operator()();\nprivate:\n ThreadPool &pool;\n};\n\n\/\/ the actual thread pool\nclass ThreadPool {\npublic:\n ThreadPool(size_t);\n template<class F>\n void enqueue(F f);\n ~ThreadPool();\nprivate:\n friend class Worker;\n\n \/\/ need to keep track of threads so we can join them\n std::vector< std::thread > workers;\n\n \/\/ the task queue\n std::queue< std::function<void()> > tasks;\n\n \/\/ synchronization\n std::mutex queue_mutex;\n std::condition_variable condition;\n bool stop;\n};\n\nvoid Worker::operator()()\n{\n std::function<void()> task;\n while(true)\n {\n { \/\/ acquire lock\n std::unique_lock<std::mutex>\n lock(pool.queue_mutex);\n\n \/\/ look for a work item\n while(!pool.stop)\n { \/\/ if there are none wait for notification\n pool.condition.wait(lock);\n }\n\n if(pool.stop && pool.tasks.empty()) \/\/ exit if the pool is stopped\n return;\n\n \/\/ get the task from the queue\n task = pool.tasks.front();\n pool.tasks.pop();\n\n } \/\/ release lock\n\n \/\/ execute the task\n task();\n }\n}\n\n\/\/ the constructor just launches some amount of workers\nThreadPool::ThreadPool(size_t threads)\n : stop(false)\n{\n for(size_t i = 0;i<threads;++i) {\n workers.push_back(std::thread(Worker(*this)));\n }\n}\n\n\/\/ the destructor joins all threads\nThreadPool::~ThreadPool()\n{\n \/\/ stop all threads\n stop = true;\n condition.notify_all();\n\n \/\/ join them\n for(size_t i = 0;i<workers.size();++i)\n workers[i].join();\n}\n\n\/\/ add new work item to the pool\ntemplate<class F>\nvoid ThreadPool::enqueue(F f)\n{\n { \/\/ acquire lock\n std::unique_lock<std::mutex> lock(queue_mutex);\n\n \/\/ add the task\n tasks.push(std::function<void()>(f));\n } \/\/ release lock\n\n \/\/ wake up one thread\n condition.notify_one();\n}<\/code><\/pre>\nDetails<\/h2>\n
1. condition_variable with predicate<\/h3>\n