• LeqxLeqx (10/10) Dec 23 2016 I've recently been attempting to detect whether or not stdin
• Nemanja Boric (40/54) Dec 23 2016 What's in the `core.sys.posix.poll` is just a C wrapper, meaning
• LeqxLeqx (5/11) Dec 23 2016 Thank you so much! That worked perfectly. It looks like the

LeqxLeqx <LeqxLeqx protonmail.ch> writes:

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

Nemanja Boric <4burgos gmail.com> writes:

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

LeqxLeqx <LeqxLeqx protonmail.ch> writes:

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!