线程中访问临界区的方法
1、信号量:控制一组对象访问时,比如从5条可用的电话线中分配一个给某个线程的情况
2、互斥锁:想控制任一时刻只能有一个线程可以访问一些共享内存
本文使用二值信号量保护临界资源
include<semaphore.h>
//创建信号量
int sem_init(sem_t *sem,int pshared,unsigned int value);
//控制信号量的值
sem_wait(sem_t * sem);//信号量的值 -1
sem_post(sem_t * sem);//给信号量的值 +1
sem_destroy(sem_t *sem);//清理信号量所有资源
临界区资源 work_area
主线程获取输入,子线程统计字符串大小
#include<stdio.h>
#include<unistd.h>
#include<string.h>
#include<stdlib.h>
#include<semaphore.h>
#include<pthread.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\n");
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 txt,Enter 'end' to finish\n");
while(strncmp("end",work_area,3) !=0)
{
fgets(work_area,WORK_SIZE,stdin);
sem_post(&bin_sem);
}
printf("\n Waiting 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);
}
打印输出
(base) wy@ubuntu:~/process$ ./thread3
Input some txt,Enter 'end' to finish
hello
You input 5 characters
end
Waiting for thread to finish...
Thread joined
(base) wy@ubun