多线程编程——屏障

屏障是多线程同步的一种方法。barrier意为屏障或者栏杆，把先后到达的多个线程挡在同一栏杆前，直到所有线程到齐，然后撤下栏杆同时放行。先到达的线程将会阻塞，等到所有调用pthread_barrier_wait()函数的线程（数量等于屏障初始化时指定的count）都到达后，这些线程才会由阻塞状态进入就绪状态再次参与系统调度。屏障是基于条件变量和互斥锁实现的。主要操作包括：调用pthread_barrier_init()初始化一个屏障，其他线程调用pthread_barrier_wait()，所有线程到期后线程唤醒进入准备状态，屏障不在使用调用pthread_barrier_destroy()销毁一个屏障

#include <pthread.h>
#include <unistd.h>
#include <stdio.h>
/* 线程控制块 */
static pthread_t tid1;
static pthread_t tid2;
static pthread_t tid3;
/* 屏障控制块 */
static pthread_barrier_t barrier;
/* 函数返回值检查函数 */
static void check_result(char* str,int result)
{
	if (0 == result)
	{
		printf("%s successfully!\n",str);
	}
	else
	{
		printf("%s failed! error code is %d\n",str,result);
	}
}
/*线程1入口函数*/
static void* thread1_entry(void* parameter)
{
	int count = 0;
	printf("thread1 have arrived the barrier!\n");
	pthread_barrier_wait(&barrier); /* 到达屏障，并等待其他线程到达 */
	while (1)
	{
		/* 打印线程计数值输出 */
		printf("thread1 count: %d\n",count ++);
		/* 休眠2秒*/
		sleep(2);
	}
}
/*线程2入口函数*/
static void* thread2_entry(void* parameter)
{
	int count = 0;
	printf("thread2 have arrived the barrier!\n");
	pthread_barrier_wait(&barrier);
	while (1)
	{
		/* 打印线程计数值输出 */
		printf("thread2 count: %d\n",count ++);
		/* 休眠2秒*/
		sleep(2);
	}
}
/* 线程3入口函数 */
static void* thread3_entry(void* parameter)
{
	int count = 0;
	printf("thread3 have arrived the barrier!\n");
	pthread_barrier_wait(&barrier);
	while (1)
	{
		/* 打印线程计数值输出 */
		printf("thread3 count: %d\n",count ++);
		/* 休眠2秒*/
		sleep(2);
	}
}
/* 用户应用入口 */
int application_init()
{
	int result;
	pthread_barrier_init(&barrier,NULL,3);
	/*创建线程1,线程入口是thread1_entry, 属性参数设为NULL选择默认值，入口参数为NULL*/
	result = pthread_create(&tid1,NULL,thread1_entry,NULL);
	check_result("thread1 created",result);
	/*创建线程2,线程入口是thread2_entry, 属性参数设为NULL选择默认值，入口参数为NULL*/
	result = pthread_create(&tid2,NULL,thread2_entry,NULL);
	check_result("thread2 created",result);
	/*创建线程3,线程入口是thread3_entry, 属性参数设为NULL选择默认值，入口参数为NULL*/
	result = pthread_create(&tid3,NULL,thread3_entry,NULL);
	check_result("thread3 created",result);
	
	
	return 0;
}
int main()
{
	int i ;
	application_init();
	i=100;
	do{
		sleep(1);
	}while(i--);
}

运行结果：

-bash-3.2$ gcc -pthread barrier.c -o 8app
-bash-3.2$ ./8app
thread1 created successfully!
thread2 created successfully!
thread3 created successfully!
thread1 have arrived the barrier!
thread2 have arrived the barrier!
thread3 have arrived the barrier!
thread1 count: 0
thread2 count: 0
thread3 count: 0
thread1 count: 1
thread2 count: 1
thread3 count: 1
thread1 count: 2
thread2 count: 2
thread3 count: 2
thread2 count: 3
thread3 count: 3
thread1 count: 3
thread2 count: 4
thread3 count: 4
thread1 count: 4
thread2 count: 5
thread3 count: 5
thread1 count: 5
thread2 count: 6
thread3 count: 6
thread1 count: 6
thread2 count: 7
thread3 count: 7
thread1 count: 7
thread2 count: 8
thread3 count: 8
thread1 count: 8
thread2 count: 9
thread3 count: 9
thread1 count: 9