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From: u-lchoqu%peruvian.utah.edu@cs.utah.edu (Lee Choquette)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Non-Blocking io (stdin & MacTCP)
Summary: use asynchronous File Mgr calls
Message-ID: <1990Nov2.194118.29698@hellgate.utah.edu>
Date: 3 Nov 90 02:41:18 GMT
References: <520@mermaid.Litle.Com>
Organization: University of Utah CS Dept
Lines: 29

In article <520@mermaid.Litle.Com> kevin@mermaid.Litle.Com
	(Kevin P. Burke) writes:

	Am I clueless or does the Mac have no non blocking io?  I'm writing
	some code and don't want to hang around in reads and getlines for
	ever.  Even poll would be nice....

Use the low-level File Manager routines described in Inside Mac
II-97-114.  You'll have to pass in a parameter block to each routine,
and specify asynchronous calling, as in

	error = PBRead (pBlock, TRUE);

If you want to poll, set pBlock.ioCompletion = NULL and poll
pBlock.ioResult, waiting until ioResult != 1.  Or you can make
pBlock.ioCompletion point at a function you want called upon
completion of the I/O request, but you must follow the restrictions on
page 99 of what routines called at interrupt level may and may not do.

The functional difference between this technique and Unix non-blocking
I/O, is that in Unix if you get the error EWOULDBLOCK you don't
necessarily have to go back later and read from the file.  On the Mac
you have a pending I/O request, and I can't find in Inside Mac a safe
way to cancel that request.  Does anyone out there know how to cancel
an asynchronous File Manager request?  What happens if your
application quits before the request completes?
Lee Choquette                   Internet: u-lchoqu@peruvian.utah.edu
3846 Barbara Wy                 Bitnet:   choquette@utahcca
Salt Lake City, UT  84124       UUCP:     utah-cs!peruvian!u-lchoqu