线程的同步互斥机制3月4日

题目：

代码：

#include <stdio.h>
#include <pthread.h>
#include <string.h>
#include <semaphore.h>
#include <unistd.h>sem_t sem1,sem2;void* callback1(void*arg)
{while(1){if(sem_wait(&sem1)<0)  //等待sem1的信号量变为可用，申请信号灯{perror("sem_wait");return NULL;}printf("%s\n",buf);if(sem_post(&sem2)<0)  //通知sem2的线程可以进行{perror("sem_post");pthread_exit(NULL);}}pthread_exit(NULL);return NULL;
}void* callback2(void*arg)
{int i,j;char temp;while(1){if(sem_wait(&sem2)<0){perror("sem_wait");return NULL;}for(i=0,j=strlen(buf)-1;i<j;i++,j--){temp = buf[i];buf[i]=buf[j];buf[j] = temp;}if(sem_post(&sem1)<0){perror("sem_post");                                                                                          pthread_exit(NULL);}}pthread_exit(NULL);return NULL;
}int main(int argc, const char *argv[])
{if(sem_init(&sem1,0,1)<0){perror("sem_init");return -1;}if(sem_init(&sem2,0,0)<0){perror("sem_init");return -1;}pthread_t A,B;pthread_create(&A,NULL,callback1,NULL);pthread_create(&B,NULL,callback2,NULL);pthread_detach(B);pthread_join(A,NULL);pthread_join (B,NULL);if(sem_destroy(&sem1)<0){perror("sem_destroy");return -1;}if(sem_destroy(&sem2)<0){perror("sem_destroy");return -1;}return 0;
}