c++ - Pthread 在信号句柄中使用 pthread_cond_wait 阻塞

Question

我想写一个程序可以停止(挂起)所有其他 pthreads 而不是主线程，我使用 pthread_kill 向目标线程发送一个信号来调用它的信号处理程序，它可以阻塞本身。但是我卡住了。下面是代码:

#include <iostream>
#include <signal.h> 
#include <pthread.h>
#include <unistd.h>
#include <cassert>

using namespace std;

pthread_mutex_t _mutex;
pthread_cond_t cond;

void cur_thread_wait(int sig)
{
    cout << pthread_self() << endl;

//  pthread_mutex_lock(&_mutex);
    pthread_cond_wait(&cond, &_mutex);  
//  pthread_mutex_unlock(&_mutex);
}

void signal_all()
{
    pthread_cond_broadcast(&cond);
}

void *print(void *)
{
    pthread_detach(pthread_self());
    for (int i = 0; i < 100; i ++) {
        cout << dec << i << endl;
    }
    return nullptr;
}


int main(int argc, char *argv[]) 
{
    pthread_mutex_init(&_mutex, nullptr);
    pthread_cond_init(&cond, nullptr);

    signal(SIGUSR1, cur_thread_wait);

    pthread_t pid1, pid2, pid3;
    pthread_create(&pid1, nullptr, print, nullptr);
    pthread_create(&pid2, nullptr, print, nullptr);
    pthread_create(&pid3, nullptr, print, nullptr);

//  usleep(400);

    pthread_kill(pid1, SIGUSR1);
    pthread_kill(pid2, SIGUSR1);
    pthread_kill(pid3, SIGUSR1);

    signal_all();


    pthread_exit(nullptr);
}

事实上，我认为真的没有必要创建一个mutex(这是真的吗？)...我是linux 编程的新手。我该如何解决这个问题？谢谢。

Answer 1

您确实需要在调用pthread_cond_wait 之前锁定互斥量；它期望它被锁定，它解锁它，等待条件变量被断言，然后在返回给你之前重新锁定它。

来自 pthread_cond_wait(3p):

int pthread_cond_wait(pthread_cond_t *restrict cond,
    pthread_mutex_t *restrict mutex);

The pthread_cond_timedwait() and pthread_cond_wait() functions shall block on a condition variable. The application shall ensure that these functions are called with mutex locked by the calling thread; otherwise, an error (for PTHREAD_MUTEX_ERRORCHECK and robust mutexes) or undefined behavior (for other mutexes) results.