Question

我读/写到由pipe(pipe_fds)创建的管道。所以基本上使用以下代码，我正在读取该管道：

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

当我得到某些东西时，我会把它打印出来：

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

我想要的是，当pipe到read上出现一段时间没有任何内容时，我想知道并做到：

printf("dummy");

这可以通过select()实现吗？关于如何做到这一点的任何指示都会很棒。

Answer 1

假设您想要等待5秒钟然后如果没有写入管道，则打印出“假”。

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
}

Answer 2

IIRC，select超时，然后您与FD_ISSET核对，以确定是否返回了I / O.

使用带管道的select（）

2 个答案: