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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Class with task destructor
Date: Thu, 01 Dec 2011 16:48:54 -0500
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Date: 2011-12-01T16:48:54-05:00
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"J-P. Rosen" <rosen@adalog.fr> writes:

> Put an entry (say "Termination_Wait") in the waited task, and never
> accept it. Call Termination_Wait from the waiting task. When the waiting
> task receives Tasking_Error, the waited task is terminated (well,
> completed, but that should be close enough).

I don't think it's close enough.  It is impossible to actually
free things before the task is really terminated.  The task is
doing finalization between completion and termination, and that
could refer to discriminants.  And even if there's no finalization
present, the task is still using its stack, which had better not
be freed.

So there's still a race condition.

Luckily, in the latest version of GNAT, if you call U_D on an
object containing tasks, it will get freed.  If the task happens
to be already terminated, it will get freed immediately.  Otherwise,
it will get freed when the task does terminate.  But this is not
required by the RM.

- Bob