Linux select/poll机制原理分析( 三 ) _Linux

3.2 测试代码测试代码逻辑：

创建一个设值线程，用于每隔2秒来设置一次count值；
主线程调用select函数监听，当设值线程设置了count值后，select便会返回；

#include <stdio.h>#include <string.h>#include <fcntl.h>#include <pthread.h>#include <errno.h>#include <unistd.h>#include <sys/ioctl.h>#include <sys/stat.h>#include <sys/types.h>#include <sys/time.h>static void *set_count_thread(void *arg){	int fd = *(int *)arg;	unsigned int count_value = https://www.isolves.com/it/rj/czxt/linux/2020-10-10/1;	int loop_cnt = 20;	int ret;	while (loop_cnt--) {ret = ioctl(fd, NOTIFY_SET_COUNT, &count_value);if (ret < 0) {printf("ioctl set count value fail:%sn", strerror(errno));return NULL;}sleep(1);	}	return NULL;}int main(void){	int fd;	int ret;	pthread_t setcnt_tid;	int loop_cnt = 20;	/* for select use */	fd_set rfds;	struct timeval tv;	fd = open("/dev/poll", O_RDWR);	if (fd < 0) {printf("/dev/poll open failed: %sn", strerror(errno));return -1;	}	/* wait up to five seconds */	tv.tv_sec = 5;	tv.tv_usec = 0;	ret = pthread_create(&setcnt_tid, NULL,set_count_thread, &fd);	if (ret < 0) {printf("set_count_thread create fail: %dn", ret);return -1;	}	while (loop_cnt--) {FD_ZERO(&rfds);FD_SET(fd, &rfds);ret = select(fd + 1, &rfds, NULL, NULL, &tv);//ret = select(fd + 1, &rfds, NULL, NULL, NULL);if (ret == -1) {perror("select()");break;}else if (ret)printf("Data is available now.n");else {printf("No data within five seconds.n");}	}	ret = pthread_join(setcnt_tid, NULL);	if (ret < 0) {printf("set_count_thread join fail.n");return -1;	}	close(fd);	return 0;}