From: Mark H Weaver <mhw@netris.org>
To: ludo@gnu.org (Ludovic Courtès)
Cc: guile-devel@gnu.org
Subject: Re: [PATCH] Futures: Avoid creating the worker pool more than once
Date: Fri, 09 Nov 2012 22:13:50 -0500 [thread overview]
Message-ID: <87ehk2rvyp.fsf@tines.lan> (raw)
In-Reply-To: <87zk2rc3kz.fsf@gnu.org> ("Ludovic \=\?utf-8\?Q\?Court\=C3\=A8s\=22'\?\= \=\?utf-8\?Q\?s\?\= message of "Thu, 08 Nov 2012 20:11:24 +0100")
ludo@gnu.org (Ludovic Courtès) writes:
> Mark H Weaver <mhw@netris.org> skribis:
>
>> + ;; setting 'create-workers!' to a no-op is an optimization, but it is
>> + ;; still possible for '%create-workers!' to be called more than once
>> + ;; from different threads. Therefore, to avoid creating %workers more
>> + ;; than once (and thus creating too many threads), we check to make
>> + ;; sure %workers is empty within the critical section.
>
> Do you have a scenario where this happens?
I'd hoped that the comment above was clear, but let me try again.
If two threads simultaneously call 'make-future' before the worker pool
has been created, then both threads can call 'create-workers!' (before
it has been rebound), and from there both can enter '%create-workers!'.
At that point, unless one of the threads is killed, it is guaranteed
that both will enter the critical section: first one, and then the other
(after the first one has unlocked the mutex). Thus, two worker pools
will be created (though the first worker pool will become inaccessible).
Mark
next prev parent reply other threads:[~2012-11-10 3:13 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-06 23:07 [PATCH] Futures: Avoid creating the worker pool more than once Mark H Weaver
2012-11-07 13:46 ` Mark H Weaver
2012-11-07 14:14 ` Daniel Hartwig
2012-11-16 23:15 ` Ludovic Courtès
2012-11-30 19:01 ` Mark H Weaver
2012-11-30 20:14 ` Ludovic Courtès
2012-11-08 19:11 ` Ludovic Courtès
2012-11-10 3:13 ` Mark H Weaver [this message]
2012-11-10 13:53 ` Ludovic Courtès
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