c - 从第二个线程不打印-带互斥锁的pthreads

我写道：

#include <pthread.h>
#include <stdio.h>
#include <sys/types.h>

pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER;

int globalVarX;

void *threadFunction (void *arg)
{
    pthread_mutex_lock (&mutex1);

    while (globalVarX < 1000)
    {
        printf("x increment by thread id: %d", gettid ());
        ++globalVarX;
    }

    pthread_mutex_unlock (&mutex1);

    return NULL;
}

int main()
{
    pthread_t threadA;
    pthread_t threadB;

    if (pthread_create (&threadA, NULL, threadFunction, NULL))
    {
        fprintf (stderr, "Error creating thread\n");
        return 1;
    }

    if (pthread_create (&threadB, NULL, threadFunction, NULL))
    {
        fprintf (stderr, "Error creating thread\n");
        return 1;
    }

    if (pthread_join (threadA, NULL))
    {
        fprintf (stderr, "Error joining thread\n");
        return 2;
    }

    if (pthread_join (threadB, NULL))
    {
        fprintf (stderr, "Error joining thread\n");
        return 2;
    }

    return 0;
}

我得到的指纹如下：

~/studies$ ./a.out
x increment by thread id: 3154
x increment by thread id: 3154
x increment by thread id: 3154
x increment by thread id: 3154
x increment by thread id: 3154
x increment by thread id: 3154
x increment by thread id: 3154
x increment by thread id: 3154
x increment by thread id: 3154
x increment by thread id: 3154
~/studies$

另一条线的指纹没有显示。

最佳答案

第一个线程将globalVarX增加到1000，而第二个线程则无需执行任何操作。
我建议：
锁定一个增量而不是整个循环。
通过调用
sched_yield()，因为如果一个线程在其时间片中从globalVarX递增到1000，那么第二个线程仍然没有打印。

#include <pthread.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/syscall.h>
#include <unistd.h>

pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER;

int globalVarX;

void *threadFunction (void *arg)
{
    int flagbreak = 0;

    for(;!flagbreak;) {
        pthread_mutex_lock (&mutex1);
        if (globalVarX >= 1000) flagbreak = 1;
        else {
            ++globalVarX;
            printf("x increment by thread id: %ld\n", syscall(SYS_gettid));
        }
        pthread_mutex_unlock (&mutex1);
        sched_yield();
    }
    return NULL;
}

int main(void)
{
    pthread_t threadA;
    pthread_t threadB;

    if (pthread_create (&threadA, NULL, threadFunction, NULL))
    {
        fprintf (stderr, "Error creating thread\n");
        return 1;
    }

    if (pthread_create (&threadB, NULL, threadFunction, NULL))
    {
        fprintf (stderr, "Error creating thread\n");
        return 1;
    }

    if (pthread_join (threadA, NULL))
    {
        fprintf (stderr, "Error joining thread\n");
        return 2;
    }

    if (pthread_join (threadB, NULL))
    {
        fprintf (stderr, "Error joining thread\n");
        return 2;
    }

    return 0;
}

关于c - 从第二个线程不打印-带互斥锁的pthreads，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/30692896/