I've recently been attempting to detect whether or not stdin would block a read if I tried. I have attempted to use the /core/sys/posix/poll.d but that seems to be always returning '1' whether or not stdin has anything on it, whereas for the corresponding program written in C, it will return 1 only if there is something on stdin.

If anyone has any suggestions, they would be much appreciated. Really all I need is a way of checking if a stream / file will block if I read it.

Thanks

What's in the `core.sys.posix.poll` is just a C wrapper, meaning if you use  functions declared there, you're just calling the same one you would do in C, so it's very likely that you're doing something different in D and C program. Here's the example that works for me:

```

void main()
{
    import core.stdc.stdio: fileno, stdin;
    import core.sys.posix.poll: poll, pollfd, POLLIN;
    import std.stdio: writeln, write, readln;
    import std.exception: enforce;

    pollfd fds;
    fds.fd = fileno(stdin);
    fds.events = POLLIN;

    for (;;)
    {
        int ret = poll(&fds, 1, -1);
        switch (ret)
        {
            case POLLIN:
                auto data = readln();
                write("Data on stdin: ", data);
                break;
            case 0:
                writeln("timeout");
                break;
            case -1:
            default:
                enforce(false, "Error");
        }
    }
}
```

> > If anyone has any suggestions, they would be much appreciated.
> Really all I need is a way of checking if a stream / file will block if I read it.

Be very careful here, poll works on the readiness principle, and POSIX enforces that the regular files are always ready for reading and writing, meaning that this will not work.

http://pubs.opengroup.org/onlinepubs/009695399/functions/poll.html

> Regular files shall always poll TRUE for reading and writing.

Nemanja

On Friday, 23 December 2016 at 11:07:49 UTC, LeqxLeqx wrote:
> I've recently been attempting to detect whether or not stdin would block a read if I tried. I have attempted to use the /core/sys/posix/poll.d but that seems to be always returning '1' whether or not stdin has anything on it, whereas for the corresponding program written in C, it will return 1 only if there is something on stdin.
>
> If anyone has any suggestions, they would be much appreciated. Really all I need is a way of checking if a stream / file will block if I read it.
>
> Thanks

On Friday, 23 December 2016 at 12:51:29 UTC, Nemanja Boric wrote:
> What's in the `core.sys.posix.poll` is just a C wrapper, meaning if you use  functions declared there, you're just calling the same one you would do in C, so it's very likely that you're doing something different in D and C program. Here's the example that works for me:
>
> [...]

Thank you so much! That worked perfectly. It looks like the problem was that I was passing in the wrong fileno and this was causing it to always return 1.

Thanks again!