[ruby-talk:12190] Re: Nonblocking Read]

On Wed, Mar 07, 2001 at 07:28:22AM +0900, Alex McHale wrote:
> > The UNIX call for doing it would be something like
> > 
> > 	fcntl(fd, F_SETFL, O_NONBLOCK)
> > 
> > In Ruby you could do
> > 
> > 	player.socket.fcntl(...)
> > 
> > but I don't know if Ruby makes the constants 'F_SETFL' or 'O_NONBLOCK'
> > available.  You probably need to look the 'fcntl' man page on your
> > system, and the 'fcntl.h' header file.
> 
> Doing some examining of the Ruby source, and it appears that O_NONBLOCK is 
> imported as File::NONBLOCK, but I can't find any reference to a varient of 
> F_SETFL, nor any pointers on where I might find an equivalent / 
> possibilities for the Ruby fcntl cmds.
> 
> With File::NONBLOCK being there, I have to assume there's a way to read 
> from a socket without blocking.

The pickaxe book documents two paramaters for IO::fcntl

	ios.fcntl(anIntegerCmd, anArg) --> anInteger

You've found File::NONBLOCK, presumably "anArg".  On OpenBSD, FreeBSD,
Linux, and Solaris '/usr/include/fcntl.h' defines 'F_SETFL' as 4, so I'd
say 4 is a good bet for "anIntegerCmd".  Now, in UNIX when you try to
read from a non-blocking file stream with read(2) ('sysread' in Ruby)
where there's no data present, or write to it with write(2) ('syswrite')
when it's not ready, you get a return value of -1 and ERRNO set to EAGAIN
or EWOULDBLOCK.  In Ruby, I presume you'd get a 'SystemCallError' that 
you'll have to trap and check.

Welcome to UNIX system programming.  The standard reference is Stevens'
'Advanced Programming in the UNIX Environment'.

David S.

> 
> If anyone out there can help..
> 
>   Alex McHale