linux用信号量进行同步
信号量一般常用来保护一段代码，使其每次只能被一个执行线程运行。
以下这段程序在主线程中，我们等待直到有文本输入，然后调用sem_post增加信号量的值，这将立刻令另一个线程从sem_wait的等待中返回并开始执行。在统计完字符个数后，它再次调用sem_wait并再次被阻塞，直到主线程再次调用sem_post增加信号量的值为止。
#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;sem_t bin_sem2;#define WORK_SIZE 1024char 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=sem_init(&bin_sem2,0,1); 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"); sem_wait(&bin_sem2); while(strncmp("end",work_area,3)!=0) { if(strncmp(work_area,"FAST",4)==0) { printf("***\n"); sem_post(&bin_sem); strcpy(work_area,"Wheeee..."); } else { fgets(work_area,WORK_SIZE,stdin); sem_post(&bin_sem); } printf("&&&\n"); //sem_post(&bin_sem); sem_wait(&bin_sem2); } 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); sem_destroy(&bin_sem2); 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_post(&bin_sem2); sem_wait(&bin_sem); } pthread_exit(NULL);}