Re: NSTask/NSPipe STDIN hangs on large data...
Re: NSTask/NSPipe STDIN hangs on large data...
- Subject: Re: NSTask/NSPipe STDIN hangs on large data...
- From: "Joe Pezzillo" <email@hidden>
- Date: Wed, 05 Feb 2003 02:35:33 -0700
Daryn-
Thanks for encouraging me to continue to look around and for leading me down
the path that used the UNIX file control commands. Finally (at 2:30am here
in Boulder, Colorado, USA), searching for an explanation for the "resource
temporarily unavailable" exception I was getting after using those UNIX
commands, I found this article:
<
http://www.omnigroup.com/mailman/archive/macosx-dev/2001-December/021997.ht
ml>
...which offers further supporting evidence of this problem and includes a
working code fragment of a solution (and from way back in 2001, to boot).
I guess I should have figured that just doing the whole file/pipe handling
in the UNIX realm would sidestep the problems I was experiencing with the
blocking NSFileHandles and NSTask/NSPipe.
Thanks again for all your help!
Joe
email@hidden
cc: Alex Raftis, author of the linked article (THANK YOU!)
On 1/29/03 7:12 PM, "Daryn" <email@hidden> wrote:
>
On Wednesday, January 29, 2003, at 06:08 PM, Joe Pezzillo wrote:
>
> Of course, I thought that's what "readInBackgroundAndNotify" was
>
> supposed to
>
> deal with in the first place for the Asynch version.
>
>
Once blocked on a write, the run loop will grind to a halt. You might
>
try spinning off another thread with the read file handle and have that
>
thread read the output. I doubt NSTask is thread-safe, but I wouldn't
>
expect any problems with the file handles.
>
>
> fileStatus = fcntl([readHandle fileDescriptor], F_SETFL, O_NONBLOCK);
>
>
>
> ... but then if I try to read right away, I get a "Resource temporarily
>
> unavailable" exception. ...
>
>
I guess NSFileHandle doesn't like 0-length reads or the EAGAIN error...
>
It's rather odd that NSFileHandle doesn't include non-blocking support.
>
>
> So then I tried using select() based on its manpage,
>
> readyFDs = select( 1, &fdreadset, nil, nil, &zeroTV );
>
>
Your first arg to select() is causing only fd 0 (stdin) to be checked.
>
Trying passing [readHandle fileDescriptor]+1. I'd recode that into a
>
selector like -(BOOL)hasAvailableData to make it more palatable.
>
>
> I truly appreciate all the time you've taken to help me with this, your
>
> insights are very valuable. If you can suggest a book or online
>
> reference
>
> for this stuff, I'll gladly devour it and spend another day testing
>
> before
>
> asking any more questions!
>
>
Almost any O'Reilly book is good. It's a bit costly ($70), but if you
>
really want to learn unix, I'd told that Richard Steven's Advanced
>
Programming in the UNIX Environment is a great book. Also try googling
>
for "unix pipe read write deadlock".
>
>
Daryn
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