Re: tasking with GNAT 3.14p on windows

[Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>]

On 31 Mar 2003 21:40:04 -0500, Robert A Duff
<bobduff@shell01.TheWorld.com> wrote:

>"Chad R. Meiners" <crmeiners@hotmail.com> writes:
>
>> "Jano" <nono@celes.unizar.es> wrote in message
>> news:MPG.18f2a01651aa20aa9896cb@News.CIS.DFN.DE...
>> > trying to know the behavior with blocking I/O. In XP with -gnatP, you
>> > get indefinite wait for user input, but if more than 10 seconds has
>> > passed when you hit enter, you get also the "aborted" print.
>> >
>> > Is that expected behavior? Gnat docs say that polling implements calls
>> > in each loop iteration / function call. Should I assume that if you
>> > haven't loops / calls, abort will never work properly?
>> 
>> It seems like reasonable behavior.  System calls are not guaranteed to be
>> abortable.
>
>The Ada RM has nothing to say about system calls, so of course they are
>not guaranteed (by the RM) to be abortable.  But I'm very interested in
>what GNAT does with system calls in the presence of abort.  Can you tell
>us what happens if, say, a socket read is aborted?  And if it's not
>abortable, how does one work around that fact?

The single solution I know is to close the socket from another task.
This causes the pending operation to complete with an error so that
the reader task might then accept a rendezous. But this is of course
not an asynchronous control transfer.

If sockets some time will be included into the standard library, then
RM should require that all blocking socket operations be abortable and
in a bounded time.

---
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de