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Newsgroups: comp.lang.ada
From: Ted Dennison<dennison@telepath.com>
References: <9r8nmb$l2j$1@e3k.asi.ansaldo.it>
Subject: Re: asynchronos select question
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NNTP-Posting-Date: Thu, 25 Oct 2001 14:57:33 EDT
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Date: Thu, 25 Oct 2001 18:57:33 GMT
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Date: 2001-10-25T18:57:33+00:00
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In article <9r8nmb$l2j$1@e3k.asi.ansaldo.it>, Paolo Argenton says...
>select
>    delay 5.0;
>    put_line (" timeout" );
>then abort
>    proc_with_blocking_io; -- i.e. wait for a byte to come from a serial
>line for istance
>end select;
>
>it never triggers the timeout part and waits forever, at least on NT+gnat

I haven't actually ever used this construct before (heck, I'd fogotten it
existed). But I'd guess that an abort of the abortable part is only possible
while you are within the language. If your Win32 thread is blocked waiting for
an I/O at the Operating System level, there is nothing Ada can do for you. So
what would probably happen here is that you will sit forever waiting for that IO
to complete. Once it does, the abortable part will get aborted, and you'd see
your "timeout" string (assuming there is still some Ada to execute after the I/O
completes).

For what you seem to be attempting to do, I think I'd use a task and a protected
type. The task services the I/O source, and the protected type implements a
queue of data read from the source. Then you can use a conditional or timed
entry call to read the data from the protected type (queue).

---
T.E.D.    homepage   - http://www.telepath.com/dennison/Ted/TED.html

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