Re: NSTask/NSPipe STDIN hangs on large data...

FROM : Daryn
DATE : Thu Jan 30 03:12:21 2003

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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