使用select()与管 [英] using select() with pipe
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问题描述
我的读/写的由创建一个管道管(pipe_fds)
。因此,与下面code,基本上,我是从这个管道读取:
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");
和当过我得到的东西,我把它打印出来由:
And when ever I get something, I print it out by:
while (fgets(buf, 200, fp)) {
printf("%s", buf);
}
我要的是,当一定时间没有任何的管道
出现读取
,我想了解它,做的:
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");
这能由选择()?如何做到这一点的任何指针将是巨大的。
Can this be achieved by select() ? Any pointers on how to do that will be great.
推荐答案
比方说,你想等待5秒钟,然后,如果没有写入到管道,你打印出虚拟。
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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