Suspend and resume one C++ thread in another

Question

I have a C++ code with two threads in it. After an event 'A' in thread 2, thread 1 should be paused(suspended), some more tasks are to be executed in thread 2 (say event 'B')and finally thread 1 should be resumed. Is there any way to do this?

My code looks something like this:

HANDLE C;
DWORD WINAPI A (LPVOID in)
{
    while(1){
        // some operation
    }
    return 0;
}

DWORD WINAPI B (LPVOID in)
{
    while(1){

        //Event A occurs here

        SuspendThread (C);

        //Event B occurs here

        ResumeThread (C);
        }
    return 0;
}

int main()
{
    C = CreateThread (NULL, 0, A, NULL, 0, NULL);
    CreateThread (NULL, 0, B, NULL, 0, NULL);
    return 0;
}

You are doing that right now, what the problem? – masoud Mar 19 '13 at 14:09 — masoud, Mar 19 '13 at 14:09
Random deadlock, no doubt. – Hans Passant Mar 19 '13 at 14:56 — Hans Passant, Mar 19 '13 at 14:56

score 10 · Answer 1 · answered Jul 13 '13 at 20:15

Hi I have an example that I got inspired from cpp reference. The example uses C++ 11 so given that this question was not flagged win32 but c++ and multithreading I post something.

First here is the original link.

http://en.cppreference.com/w/cpp/thread/sleep_for

Now here is the code I got that solves the problem.

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

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

void ThreadB_Activity()
{
    // Wait until ThreadA() sends data
    {
        std::unique_lock<std::mutex> lk(m);
        cv.wait(lk, []{return ready;});
    }

    std::cout << "Thread B is processing data\n";
    data += " after processing";
    // Send data back to ThreadA through the condition variable
    {
        std::lock_guard<std::mutex> lk(m);
        processed = true;
        std::cout << "Thread B signals data processing completed\n";
    }
    cv.notify_one();
}


void ThreadA_Activity()
{
    std::cout<<"Thread A started "<<std::endl;
    data = "Example data";
    // send data to the worker thread
    {
        std::lock_guard<std::mutex> lk(m);
        ready = true;
        std::cout << "Thread A signals data are ready to be processed\n";
    }
    cv.notify_one();//notify to ThreadB that he can start doing his job

    // wait for the Thread B
    {
        std::unique_lock<std::mutex> lk(m);
        cv.wait(lk, []{return processed;});
    }
    std::cout << "Back in Thread A , data = " << data << '\n';

    std::this_thread::sleep_for( std::chrono::milliseconds( 1000 ));
    std::cout<<"end of Thread A"<<std::endl;
}


int main()
{
    std::thread ThreadB(ThreadB_Activity);
    std::thread ThreadA(ThreadA_Activity);

    ThreadB.join();
    ThreadA.join();

    std::cout << "Back in main , data = " << data << '\n';
    return 0;
}

Hope that helps, any comments are welcome :-)

score 0 · Answer 2 · edited May 23 '17 at 12:08

Since you seem to be using win32 you can use an event

If you want to do something similar in pthreads there is an example here.

In both cases thread A will test a condition/event (and wait if it is set or continue if it is not) and thread B will set and clear the condition/event. Note you might also need a mutex between thread A and B depending on what they are doing, can they corrupt each other?

Suspend and resume one C++ thread in another

2 Answers2