多线程和使用事件

Question

while (1)
{
    if (!msg_in.empty())
    {
        //processes 
        msg_map[i][j].push(); //i and j are int (irrelevant here)
    }

}

线程3：

while (1)
{
    if (msg_map.find(i) != msg_map.end())
    {
        if (!msg_map[i].find(j)->second.empty())
        {
            //processes 
        }
    }
}

Answer 1

你的问题是生产者和消费者的问题。可以对事件使用条件变量。这里有一个例子：http://en.cppreference.com/w/cpp/thread/condition_variable

如果你需要的话，我已经把它改编成你的例子了。

#include "MainThread.h"


#include <iostream>
#include <string>
#include <thread>
#include <mutex>
#include <atomic>
#include <condition_variable>

std::mutex m;
std::condition_variable cv;
bool ready = false;
bool processed = false;

void worker_thread(unsigned int threadNum)
{
    // Wait until main() sends data
    {
        std::unique_lock<std::mutex> lk(m);
        cv.wait(lk, []{return ready;});
    }

    std::cout << "Worker thread "<<threadNum <<" is processing data"<<std::endl;

    // Send data back to main()
    {
        std::lock_guard<std::mutex> lk(m);
        processed = true;
        std::cout << "Worker thread "<< threadNum <<" signals data processing completed\n";
    }
    cv.notify_one();
}


int initializeData()
{
    // send data to the worker thread
    {
        std::lock_guard<std::mutex> lk(m);
        ready = true;
        std::cout << "Data initialized"<<std::endl;
    }
    cv.notify_one();
    return 0;
}

int consumerThread(unsigned int nbThreads)
{
    std::atomic<unsigned int> nbConsumedthreads=0;
    while (nbConsumedthreads<nbThreads)
    {
        std::unique_lock<std::mutex> lk(m);
        cv.wait(lk, []{return processed;});
        std::cout<<"Data processed counter="<<nbConsumedthreads << " "<<  std::endl;
        ++nbConsumedthreads;
        cv.notify_one();
    }

    return 0;
}

int main()
{
    const unsigned int nbThreads=3;
    std::thread worker1(worker_thread,1);
    std::thread worker2(worker_thread,2);
    std::thread worker3(worker_thread,3);

    std::thread init(initializeData);

    std::thread consume(consumerThread, nbThreads);



    worker1.join();
    worker2.join();
    worker3.join();

    init.join();

    consume.join();

    return 0;
}

希望有帮助，如果你需要更多的信息告诉我。