线程的条件变量实例

最新推荐文章于 2023-09-19 11:17:42 发布

fulinux

最新推荐文章于 2023-09-19 11:17:42 发布

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分类专栏： Linux函数篇文章标签： pthread mutex cond pthread_cond_wait 条件变量

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本博客详细介绍了如何通过多线程编程实现出租车调度系统，包括乘客到达请求、司机响应以及乘客与司机间的交互过程。通过使用信号量、互斥锁和条件变量，系统能够高效地协调乘客和司机之间的资源分配。

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情景1：

Jack开着一辆出租车来到一个站点停车，看见没人就走了。过段时间，Susan来到站点准备乘车，但是没有来，于是就等着。过了一会Mike开着车来到了这个站点，Sunsan就上了Mike的车走了。如图所示：

程序实现该情景：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>

pthread_cond_t taxicond = PTHREAD_COND_INITIALIZER;
pthread_mutex_t taximutex = PTHREAD_MUTEX_INITIALIZER;

void *traveler_arrive(void *name)
{
    char *p = (char *)name;

    printf ("Travelr: %s need a taxi now!\n", p);
    pthread_mutex_lock(&taximutex);
    pthread_cond_wait(&taxicond, &taximutex);
    pthread_mutex_unlock(&taximutex);
    printf ("traveler: %s now got a taxi!\n", p);
    pthread_exit(NULL);
}

void *taxi_arrive(void *name)
{
    char *p = (char *)name;
    printf ("Taxi: %s arrives.\n", p);
    pthread_cond_signal(&taxicond);
    pthread_exit(NULL);
}

int main (int argc, char **argv)
{
    char *name;
    pthread_t thread;
    pthread_attr_t threadattr;
    pthread_attr_init(&threadattr);

    name = "Jack";
    pthread_create(&thread, &threadattr, taxi_arrive, name);
    sleep(1);
    name = "Susan";
    pthread_create(&thread, &threadattr, traveler_arrive, name);
    sleep(1);
    name = "Mike";
    pthread_create(&thread, &threadattr, taxi_arrive, name);
    sleep(1);

    return 0;
} /* ----- End of main() ----- */

情景2：

Jack开着一辆出租车来到一个站点停车，看见没人就等着。过段时间，Susan来到站点准备乘车看见了Jack的出租车，于是就上去了。过了一会Mike开着车来到了这个站点，看见没人救等着。如图所示：

程序实现该情景：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>

int travelercount = 0;
pthread_cond_t taxicond = PTHREAD_COND_INITIALIZER;
pthread_mutex_t taximutex = PTHREAD_MUTEX_INITIALIZER;

void *traveler_arrive(void *name)
{
    char *p = (char *)name;

    pthread_mutex_lock(&taximutex);

    printf ("traveler: %s need a taxi now!\n", p);
    travelercount++;
    pthread_cond_wait(&taxicond, &taximutex);
            
    pthread_mutex_unlock(&taximutex);
    printf ("traveler: %s now got a taxi!\n", p);
    pthread_exit(NULL);
}

void *taxi_arrive(void *name)
{
    char *p = (char *)name;
    printf ("Taxi: %s arrives.\n", p);
    for(;;){
        if(travelercount){
            pthread_cond_signal(&taxicond);
            travelercount--;
            break;
        }
    }

    pthread_exit(NULL);
}

int main (int argc, char **argv)
{
    char *name;
    pthread_t thread;
    pthread_attr_t threadattr;
    pthread_attr_init(&threadattr);

    name = "Jack";
    pthread_create(&thread, &threadattr, taxi_arrive, name);
    sleep(1);
    name = "Susan";
    pthread_create(&thread, &threadattr, traveler_arrive, name);
    sleep(3);
    name = "Mike";
    pthread_create(&thread, &threadattr, taxi_arrive, name);
    sleep(4);

    return 0;
} /* ----- End of main() ----- */

author: fulinux

E-mail: fulinux@sina.com

blog: blog.youkuaiyun.com/fulinus