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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: protected objects and external call
Date: 23 Jan 2004 12:19:49 -0500
Organization: The World Public Access UNIX, Brookline, MA
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"Jean-Pierre Rosen" <rosen@adalog.fr> writes:

> "Robert A Duff" <bobduff@shell01.TheWorld.com> a �crit dans le message de
> > > This is why it is considered a potentially blocking operation, and as
> > > such disallowed in a protected operation.
> >
> > No, I don't think that's quite right.  Entry calls are potentially
> > blocking, and you're not supposed to call them from inside a protected
> > procedure.  (Actually, it's a bounded error, and some compilers allow
> > it.)  But a protected procedure can call another protected procedure
> > with an external call.  It's up to the programmer to make sure it's not
> > the same protected object.  (You also have to obey the priority
> > ceiling rules.)
> >
> > In other words, merely grabbing the lock of a PO is *not* considered
> > blocking or potentially blocking in Ada, and no queue-ing need be
> > involved.
> >
> 9.5.1(16): [Potentially blocking operations]
> an external call on a protected subprogram (or an external requeue)
> with the same target object as that of the protected action;

Ah, thanks, I had forgotten that.  Note that this is *only* talking
about the deadlocking case -- it's just fine to call some other PO's
procedures, and you can't detect this at compile time.  The AARM
explains, "This is really a deadlocking call, not a blocking call...."

- Bob