posix 线程（2）信号量同步

#include<semaphore.h>
int sem_init(sem_t *sem , int pshared , unsigned int value);

这个函数初始化有sem指向的信号量对象，设置它的共享选项，并给它一个初始化的整数值。pshared参数控制信号量的类型，如果其值为 0，

就表示这个信号量是当前进程的局部信号量。否则这个信号量就可以在多个线程之间共享。

#include<semaphore.h>
int sem_wait(sem_t *sem);
int sem_post(sem_t *sem);

这两个函数都以一个指针为参数，该指针指向的对象是由sem_init调用初始化的信号量。

sem_post函数的作用是以原子操作的方式给信号量的值加1.

sem_post函数的作用是以原子操作的方式给信号量的值减1.

#include<semaphore.h>
int sem_destroy(sem_t *sem);

这个函数的作用是用完信号量后对它进行清理。

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <semaphore.h>void *thread_function(void *arg);
sem_t bin_sem;#define WORK_SIZE 1024
char work_area[WORK_SIZE];int main() {int res;pthread_t a_thread;void *thread_result;res = sem_init(&bin_sem, 0, 0);if (res != 0) {perror("Semaphore initialization failed");exit(EXIT_FAILURE);}res = pthread_create(&a_thread, NULL, thread_function, NULL);if (res != 0) {perror("Thread creation failed");exit(EXIT_FAILURE);}printf("Input some text. Enter 'end' to finish\n");while(strncmp("end", work_area, 3) != 0) {fgets(work_area, WORK_SIZE, stdin);sem_post(&bin_sem);}printf("\nWaiting for thread to finish...\n");res = pthread_join(a_thread, &thread_result);if (res != 0) {perror("Thread join failed");exit(EXIT_FAILURE);}printf("Thread joined\n");sem_destroy(&bin_sem);exit(EXIT_SUCCESS);
}void *thread_function(void *arg) {sem_wait(&bin_sem);while(strncmp("end", work_area, 3) != 0) {printf("You input %d characters\n", strlen(work_area) -1);sem_wait(&bin_sem);}pthread_exit(NULL);
}