C ++：使用互斥体和条件变量控制线程执行顺序 [英] C++: Control order of thread execution with mutex's and conditional variables

问题描述

此问题是对此问题的跟进。 a>。我想要线程执行一些工作，并按顺序传递句柄到下一个线程。当尝试执行以下代码时，我会在ConsoleApplication9.exe中获得

未处理的异常0x0F7C1F5F（msvcp120d.dll）：0xC0000005：访问冲突读取位置0x00000004。

  #includestdafx.h
 #include< iostream> 
 #include< thread> 
 #include< mutex> 
 #include< chrono> 
 #include< condition_variable> 
 
 std :: mutex * m_pMutexs; 
 std :: condition_variable * m_pCVs; 
 int m_pCurrentWorker; 
 
 void func（int i）
 {
 int cvCurrentInd = i; 
 std :: mutex * pCurMutex =& m_pMutexs [cvCurrentInd]; 
 
 std :: condition_variable * pCuCV =（std :: condition_variable *）（m_pCurrentWorker + i * sizeof（std :: condition_variable））; 
 
 std :: unique_lock< std :: mutex> lk（m_pMutexs [i]）; 
 
 while（i！= m_pCurrentWorker）
 {
 pCuCV-> wait（lk）; 
} 
 
 std :: cout<< 进入线程< std :: this_thread :: get_id（）<< std :: endl; 
 std :: this_thread :: sleep_for（std :: chrono :: seconds（rand（）％10））; 
 std :: cout<< 留下螺纹< std :: this_thread :: get_id（）<< std :: endl; 
 
 m_pCurrentWorker ++; 
 lk.unlock（）; 
 pCuCV-> notify_one（）; 
 
} 
 
 int _tmain（int argc，_TCHAR * argv []）
 {
 m_pMutexs = new std :: mutex [3] 
 
 m_pCVs = new std :: condition_variable [3]; 
 
 m_pCurrentWorker = 0; 
 
 srand（（unsigned int）time（0））; 
 
 std :: thread t1（func，0）; 
 std :: thread t2（func，1）; 
 std :: thread t3（func，2）; 
 
 t1.join（）; 
 t2.join（）; 
 t3.join（）; 
 
 return 0; 
} 
  

解决方案

 <$ c $ 
 
 
 < c> std :: condition_variable * pCuCV =（std :: condition_variable *）（m_pCurrentWorker + i * sizeof（std :: condition_variable））; 
  

我认为你应该写：

  std :: condition_variable * pCuCV =& m_pCVs [i]; 
  

整个函数可能是这样的：

  void func（int i）
 {
 std :: mutex * pCurMutex =& m_pMutexs [i]; 
 
 std :: condition_variable * pCuCV =& m_pCVs [i]; 
 
 std :: unique_lock< std :: mutex> lk（m_pMutexs [i]）; 
 
 while（i！= m_pCurrentWorker）{
 pCuCV-> wait（lk）; 
} 
 
 std :: cout<< 进入线程< std :: this_thread :: get_id（）<< std :: endl; 
 std :: this_thread :: sleep_for（std :: chrono :: seconds（rand（）％2））; 
 std :: cout<< 留下螺纹< std :: this_thread :: get_id（）<< std :: endl; 
 
 m_pCurrentWorker ++; 
 lk.unlock（）; 
 if（m_pCurrentWorker> 2）{
 return; 
} 
 pCuCV =& m_pCVs [m_pCurrentWorker]; 
 pCuCV-> notify_one（）; 
 
} 
  

This question is a follow up for this question. I want threads to perform some work and pass handle to the next thread in order. When trying to execute the following code, I get

Unhandled exception at 0x0F7C1F5F (msvcp120d.dll) in ConsoleApplication9.exe: 0xC0000005 : Access violation reading location 0x00000004.

    #include "stdafx.h"
    #include <iostream>
    #include <thread>
    #include <mutex>
    #include <chrono>
    #include <condition_variable> 

    std::mutex* m_pMutexs;
    std::condition_variable* m_pCVs;
    int m_pCurrentWorker;

    void func(int i)
    {
        int cvCurrentInd = i;
        std::mutex* pCurMutex = &m_pMutexs[cvCurrentInd];

        std::condition_variable* pCuCV = (std::condition_variable*)(m_pCurrentWorker + i*sizeof(std::condition_variable));

        std::unique_lock<std::mutex> lk(m_pMutexs[i]);

        while (i != m_pCurrentWorker)
        {
            pCuCV->wait(lk);
        }

        std::cout << "entered thread " << std::this_thread::get_id() << std::endl;
        std::this_thread::sleep_for(std::chrono::seconds(rand() % 10));
        std::cout << "leaving thread " << std::this_thread::get_id() << std::endl;

        m_pCurrentWorker++;
        lk.unlock();
        pCuCV->notify_one();

    }

    int _tmain(int argc, _TCHAR* argv[])
    {
        m_pMutexs = new std::mutex[3];

        m_pCVs = new std::condition_variable[3];

        m_pCurrentWorker = 0;

        srand((unsigned int)time(0));

        std::thread t1(func,0);
        std::thread t2(func,1);
        std::thread t3(func,2);

        t1.join();
        t2.join();
        t3.join();

        return 0;
    }

解决方案

Have no idea what you're trying to do but

You're casting integer to pointer?

std::condition_variable* pCuCV = (std::condition_variable*)(m_pCurrentWorker + i*sizeof(std::condition_variable));

I think you should write instead:

std::condition_variable* pCuCV = &m_pCVs[i];

The whole function could be something like this:

void func(int i)
{
    std::mutex* pCurMutex = &m_pMutexs[i];

    std::condition_variable* pCuCV = &m_pCVs[i];

    std::unique_lock<std::mutex> lk(m_pMutexs[i]);

    while (i != m_pCurrentWorker) {
        pCuCV->wait(lk);
    }

    std::cout << "entered thread " << std::this_thread::get_id() << std::endl;
    std::this_thread::sleep_for(std::chrono::seconds(rand() % 2));
    std::cout << "leaving thread " << std::this_thread::get_id() << std::endl;

    m_pCurrentWorker++;
    lk.unlock();
    if (m_pCurrentWorker > 2) {
        return;
    }
    pCuCV = &m_pCVs[m_pCurrentWorker];
    pCuCV->notify_one();

}

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