mutex.c

基于网络编程的例子

/*
 * mutex.c - Using mutexes
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <errno.h>

#define INDEX 10000000

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
long int ticks;
time_t end_time;

/* An "index" thread to increment a counter */
void idx_th(void *arg);

/* A "monitor" thread to check the counter's value */
void mon_th(void *arg);

int main (int argc, char *argv[])
{
    pthread_t idx_th_id;
    pthread_t mon_th_id;
    int ret;

    end_time = time(NULL) + 30; /* 30 second runtime*/

    /* Create two threads */
    ret = pthread_create(&idx_th_id, NULL, (void *)idx_th, NULL);
    if (ret != 0) {
        perror("pthread_create: idx_th");
        exit(EXIT_FAILURE);
    }
    ret = pthread_create(&mon_th_id, NULL, (void *)mon_th, NULL);
    if (ret != 0) {
        perror("pthread_create: mon_th");
        exit(EXIT_FAILURE);
    }

    pthread_join (idx_th_id, NULL);
    pthread_join (mon_th_id, NULL);

    exit(EXIT_SUCCESS);
}

void idx_th(void *arg)
{
    long l;

    while(time(NULL) < end_time) {
        /* Lock the mutex */
        if(pthread_mutex_lock(&mutex) != 0) {
            perror("pthread_mutex_lock");
            exit(EXIT_FAILURE);
        }

        /*.Increment the counter */
        for(l = 0l; l < INDEX; ++l)
            ++ticks;

        /* Now we're done, so unlock the mutex */
        if(pthread_mutex_unlock (&mutex) != 0) {
            perror("pthread_mutex_unlock");
            exit(EXIT_FAILURE);
        }    
        sleep(1);
    }
}

void mon_th(void *arg)
{
    int nolock = 0;
    int ret;

    while(time(NULL) < end_time) {
        /* Wake up every two seconds */
        sleep(2);
        /* Try to lock the mutex */
        ret = pthread_mutex_trylock(&mutex);
        if(ret != EBUSY) {
            if(ret != 0) {
                perror("pthread_mutex_trylock");
                exit(EXIT_FAILURE);
            }
            printf ("mon_th: got lock at %ld ticks\n", ticks);
            if(pthread_mutex_unlock(&mutex) != 0) {
                perror("pthread_mutex_unlock");
                exit(EXIT_FAILURE);
            }

        } else {
            /* Number of times mutex was locked */
            nolock++;
        }
    }
    printf ("mon_th missed lock %d times\n", nolock);
}