使用Linux C select系统调用来监视文件 [英] Using Linux C select system call to monitor files

问题描述

我在以下代码的执行文件夹中创建两个文件，一个名为 test ，另一个名为 test2 .我在一个终端中运行以下代码，该终端监视"这两个文件的更改，但是即使没有触摸该文件，select调用也会一直返回.

I creates two files in the execution folder of the following code, one named test and the other is test2. I run the following code in one terminal which "monitors" those two files for changes, but the select call returns all the time even when the file is not touched.

#include <fcntl.h>      /* fcntl */
#include <sys/select.h> /* select */
#include <stdio.h> /* NULL */

int main() {

    fd_set readfds, writefds;
    int max_fd;

    int fd_1 = open("test", O_RDWR  | O_NONBLOCK);
    int fd_2 = open("test2", O_RDWR | O_NONBLOCK);

    if(fd_1 == -1)
        return -1;

    if(fd_2 == -1)
        return -1;


    while(1) {

        FD_ZERO(&readfds);
        FD_ZERO(&writefds);

        FD_SET(fd_1, &readfds);
        FD_SET(fd_2, &readfds);
        FD_SET(fd_1, &writefds);
        FD_SET(fd_2, &writefds);

        max_fd = (fd_2 > fd_1 ? fd_2 : fd_1) + 1;

        int t_rdy = select(max_fd, &readfds, &writefds, NULL, NULL);

        if(t_rdy == -1)
            return -1;

        int t_fd;
        for(t_fd = 0; t_fd < max_fd; t_fd++) {

            if(t_fd <= 2) continue;

            printf("READ  LIST %d: %s \n", t_fd, (FD_ISSET(t_fd, &readfds) ? "set" : "nope"));
            printf("WRITE LIST %d: %s \n", t_fd, (FD_ISSET(t_fd, &writefds) ? "set" : "nope"));
        }

    }

    return 0;
}

推荐答案

这正是我所期望的行为.就 select()而言，磁盘文件总是 可供读取或写入.

This is exactly the behavior I would expect. As far as select() is concerned, disk files are always ready to be read from or written to.

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