信号量

信号量函数的名字都以sem_开头，并不像大多数线程函数那样以pthread_开头。
线程中使用的基本信号量有四个，它们都非常的简单。
#include <semaphore.h>
int sem_init(sem_t *sem,int pshared,unsigned int value);

int sem_wait(sem_t *sem);

int sem_post(sem_t *sem);

sem_post函数的作用是以原子方式给信号量的值加1.
所谓原子操作是指，如果两个线程企图同时给一个信号量加1，它们之间不会互相干扰。
sem_wait函数以原子方式将信号量的值减1.
int sem_destroy(sem_t *sem);

 

#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 *args)
{
    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);
}

Input some text.Enter 'end' to finish

The Wasp Factory

You  input  16 characters

Iain  Banks

You input 10 characters

end

 

Waiting  for thread to finish...

Thread  joined