Re: asynchronos select question

["Peter Hend�n" <phenden@tdab.com>]

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"Paolo Argenton" wrote:
<snip>
> 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
> 3.13. Is it correct ? incorrect ? my misunderstanding ? compiler/OS
> dependant code ?
Check out "pragma Polling" in the GNAT Reference Manual and the switch
-gnatP in the User's Guide. An asynchronous abort will not work at all under
NT without pragma polling (ON).

In this particular case it will not work correctly (at least not under NT)
anyway. The blocking_io call is "outside the reach" of Ada, since
no polling can take place with the process blocked in I/O.

If you replace the blocking io call with a very time-consuming calculation,
it will work just fine with Polling (ON) but not with (OFF) - the default.

Just a question to those who might know. Is this behaviour conforming
to the standard? I can see no reason in the ARM for not being able
to abort a blocking io operation. Does it work on other platforms?

Regards,
Peter H.

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