使用condition variable实现线程之间同步

发现了，这个condition variable真是个好东西啊。

 

先上代码：

#include <pthread.h>
#include <syslog.h>
#include <fcntl.h>
#include <sys/resource.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <signal.h>
#include <stdlib.h>
#include <stdio.h>
#include <termios.h>
#include <unistd.h>

struct msg {
    struct msg *m_next;
    /* ... more stuff here ... */
    int         num;
};
struct msg *workq;
pthread_cond_t qready = PTHREAD_COND_INITIALIZER;
pthread_mutex_t qlock = PTHREAD_MUTEX_INITIALIZER;

struct msg *
dequeue_msg(void)
{
    struct msg *mp;

    pthread_mutex_lock(&qlock);
    while (workq == NULL)
        pthread_cond_wait(&qready, &qlock);
    mp = workq;
    workq = mp->m_next;
    pthread_mutex_unlock(&qlock);
    /* now process the message mp */

    return mp;
}

void
enqueue_msg(struct msg *mp)
{
    pthread_mutex_lock(&qlock);
    mp->m_next = workq;
    workq = mp;
    pthread_mutex_unlock(&qlock);
    pthread_cond_signal(&qready);
}

void
cleanup(void *arg)
{
    printf("cleanup: %s/n", (char *)arg);
}

void *
thr_fn1(void *arg)
{
    int         i;
    struct msg* message;
    printf("thread 1 start, enqueue task/n");
    for (i=0; i<10; i++)
    {
        sleep(i);
        message = (struct msg*)malloc(sizeof(struct msg));
        message->num = i;
        enqueue_msg(message);
    }
    pthread_exit((void *)1);
}

void *
thr_fn2(void *arg)
{
    int         i;
    struct msg* message;
    printf("thread 2 start, dequeue task/n");
    for (;;)
    {
        message = dequeue_msg();
        printf("thread 2 get message: %d/n", message->num);

        free(message);
    }
    pthread_exit((void *)2);
}

int
main(void)
{
    int         err;
    pthread_t   tid1, tid2;
    void        *tret;

    err = pthread_create(&tid1, NULL, thr_fn1, (void *)1);
    if (err != 0)
        printf("can't create thread 1: %s/n", strerror(err));
    err = pthread_create(&tid2, NULL, thr_fn2, (void *)1);
    if (err != 0)
        printf("can't create thread 2: %s/n", strerror(err));
    err = pthread_join(tid1, &tret);
      if (err != 0)
        printf("can't join with thread 1: %s/n", strerror(err));
    printf("thread 1 exit code %d/n", (int)tret);
    err = pthread_join(tid2, &tret);
    if (err != 0)
        printf("can't join with thread 2: %s/n", strerror(err));
    printf("thread 2 exit code %d/n", (int)tret);
    exit(0);
}

 

执行的结果是
$./thread
thread 1 start, enqueue task
thread 2 start, dequeue task
thread 2 get message: 0
thread 2 get message: 1
thread 2 get message: 2
thread 2 get message: 3
thread 2 get message: 4
thread 2 get message: 5
thread 2 get message: 6
thread 2 get message: 7
thread 2 get message: 8
thread 1 exit code 1
thread 2 get message: 9