将 select() 与管道一起使用

发布于 2024-11-28 03:57:55 字数 497 浏览 0 评论 0原文

我正在读取/写入由pipe(pipe_fds)创建的管道。因此，基本上使用以下代码，我从该管道中读取：

fp = fdopen(pipe_fds[0], "r");

每当我得到一些东西时，我都会通过以下方式打印出来：

while (fgets(buf, 200, fp)) {
    printf("%s", buf);
}

我想要的是，当在一定时间内管道上没有出现任何内容时， 阅读，我想了解它并执行以下操作：

printf("dummy");

这可以通过选择（）？任何关于如何做到这一点的指示都会很棒。

原文

I am reading/writing to a pipe created by pipe(pipe_fds). So basically with following code, I am reading from that pipe:

fp = fdopen(pipe_fds[0], "r");

And when ever I get something, I print it out by:

while (fgets(buf, 200, fp)) {
    printf("%s", buf);
}

What I want is, when for certain amount of time nothing appears on the pipe to read from, I want to know about it and do:

printf("dummy");

Can this be achieved by select() ? Any pointers on how to do that will be great.

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标点 2024-12-05 03:57:55

假设您想等待 5 秒钟，然后如果没有任何内容写入管道，则打印出“dummy”。

fd_set set;
struct timeval timeout;

/* Initialize the file descriptor set. */
FD_ZERO(&set);
FD_SET(pipe_fds[0], &set);

/* Initialize the timeout data structure. */
timeout.tv_sec = 5;
timeout.tv_usec = 0;

/* In the interest of brevity, I'm using the constant FD_SETSIZE, but a more
   efficient implementation would use the highest fd + 1 instead. In your case
   since you only have a single fd, you can replace FD_SETSIZE with
   pipe_fds[0] + 1 thereby limiting the number of fds the system has to
   iterate over. */
int ret = select(FD_SETSIZE, &set, NULL, NULL, &timeout);

// a return value of 0 means that the time expired
// without any acitivity on the file descriptor
if (ret == 0)
{
    printf("dummy");
}
else if (ret < 0)
{
    // error occurred
}
else
{
    // there was activity on the file descripor
}

Let's say you wanted to wait 5 seconds and then if nothing was written to the pipe, you print out "dummy."

fd_set set;
struct timeval timeout;

/* Initialize the file descriptor set. */
FD_ZERO(&set);
FD_SET(pipe_fds[0], &set);

/* Initialize the timeout data structure. */
timeout.tv_sec = 5;
timeout.tv_usec = 0;

/* In the interest of brevity, I'm using the constant FD_SETSIZE, but a more
   efficient implementation would use the highest fd + 1 instead. In your case
   since you only have a single fd, you can replace FD_SETSIZE with
   pipe_fds[0] + 1 thereby limiting the number of fds the system has to
   iterate over. */
int ret = select(FD_SETSIZE, &set, NULL, NULL, &timeout);

// a return value of 0 means that the time expired
// without any acitivity on the file descriptor
if (ret == 0)
{
    printf("dummy");
}
else if (ret < 0)
{
    // error occurred
}
else
{
    // there was activity on the file descripor
}

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