互斥锁

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<unistd.h>
#include<pthread.h>
pthread_mutex_t mutex_x = PTHREAD_MUTEX_INITIALIZER;
int total_ticket_num = 20;
void *sell_ticket(void *arg) {
    for (int i = 0; i < 20; i++) {
        pthread_mutex_lock(&mutex_x);
        if (total_ticket_num > 0) {
            sleep(1);
            printf("sell the %dth ticket\n", 21 - total_ticket_num);
            total_ticket_num--;
        }
        pthread_mutex_unlock(&mutex_x);
    }
    return 0;
}
int main() {
    int iRet;
    pthread_t tids[4];
    int i = 0; for (i = 0; i < 4; i++) {
        int iRet = pthread_create(&tids[i], NULL, &sell_ticket, NULL);
        if (iRet) {
            printf("pthread_create error, iRet=%d\n", iRet);
            return iRet;
        }
    }
    sleep(30);
    void *retval;
    for (i = 0; i < 4; i++) {
        iRet = pthread_join(tids[i], &retval);
        if (iRet) {
            printf("tid = %d,join error, iRet=%d\n",tids[i], iRet);
            return iRet;
        }
        printf("retval = %ld\n", (long*)retval);
    }
    return 0;
}