运用条件变量保持线程同步

线程同步手段：互斥锁，读写锁，条件变量。

本文实例利用条件变量保持读写同步

#include <pthread.h>#include <stdio.h>#include <stdlib.h>#include <string.h>//#define THREAD_SYNC_PROTECTstruct msg {    struct msg *m_next;    char context[100];};struct msg *workq = NULL;int flag = 1;pthread_cond_t qready = PTHREAD_COND_INITIALIZER;pthread_mutex_t qlock = PTHREAD_MUTEX_INITIALIZER;void process_msg(void){    struct msg *mp = NULL;    for (;;) {#if defined THREAD_SYNC_PROTECT        /* protect condition varialbe without missing any condition change */        pthread_mutex_lock(&qlock);        while (workq == NULL) {            /* append thread to wait queue and make thread sleep, finally unlock mutex */            pthread_cond_wait(&qready, &qlock);            /* relock mutex when function "pthread_cond_wait" returns */            printf("condition match!\n");        }#endif        if (workq != NULL) {            mp = workq;            workq = mp->m_next;        }#if defined THREAD_SYNC_PROTECT        pthread_mutex_unlock(&qlock);#endif        if (workq != NULL) {            /* process message */            printf("thread %u :receive message %s\n", pthread_self(), mp->context);            free(mp);        }    }}void enqueue_msg(struct msg *mp){    /* Get right to operate queue */    pthread_mutex_lock(&qlock);    mp->m_next = workq;    workq = mp;    pthread_mutex_unlock(&qlock);    pthread_cond_signal(&qready);}void send_msg(void){    int i;    for (i = 0; i < 10; i++) {        struct msg *mp = malloc(sizeof(struct msg));        if (NULL == mp) {            printf("malloc failed!\n");            break;        }        sprintf(mp->context, "%s[%d] request", "customer", i);        enqueue_msg(mp);        sleep(1);    }    flag = 0;}int main(void){    pthread_t tid_send, tid_process1, tid_process2;    int ret ;    pthread_mutex_init(&qlock, NULL);    ret = pthread_create(&tid_process2, NULL, process_msg, NULL);    if (ret != 0) {        printf("create pthread send_msg failed!\n");        return -1;    }    ret = pthread_create(&tid_process1, NULL, process_msg, NULL);    if (ret != 0) {        printf("create pthread send_msg failed!\n");        return -1;    }    ret = pthread_create(&tid_send, NULL, send_msg, NULL);    if (ret != 0) {        printf("create pthread send_msg failed!\n");        return -1;    }    while(flag);    return 0;}