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);}