From: Grant Edwards <firstname.lastname@example.org>
Subject: [ECOS] Re: Once again, I need a binary semaphore
Date: Tue, 17 Mar 2015 14:47:00 -0000 [thread overview]
Message-ID: <email@example.com> (raw)
On 2015-03-17, Grant Edwards <firstname.lastname@example.org> wrote:
> On 2015-03-17, lesc <email@example.com> wrote:
>> On 16.03.2015 18:17, Grant Edwards wrote:
>>> Once again, I find I need a binary semaphore for a C application I'm
>>> porting from another OS.
>> And just using a mutex is not a option? (Sorry if you allready ruled
>> that out, but you didn't metion why youd need that specific
> The Semaphore is used so that one thread can wait for completion of a
> task that was farmed out to different thread: Thread A waits on the
> semaphore until thread B posts. It's an inter-thread signalling
> mechanism, not a mutual-exclusion mechansim.
Perhaps I should be a bit more detailed: a Mutex is owned by the
thread that calls cyg_mytex_lock(), and it can't be unlocked by a
different thread. This enforcement of ownership prevents a mutex from
being used in place of a binary semaphore for inter-thread signalling.
I've run across situations in the past where I needed to use a
semaphore for mutual exclusion, but a counting semaphore initialized
to 1 works fine for that as long as you only release the resource once
after acquiring it (not usually a problem).
Grant Edwards grant.b.edwards Yow! World War III?
at No thanks!
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next prev parent reply other threads:[~2015-03-17 14:47 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-16 17:18 [ECOS] " Grant Edwards
2015-03-17 9:21 ` lesc
2015-03-17 14:33 ` [ECOS] " Grant Edwards
2015-03-17 14:47 ` Grant Edwards [this message]
2015-03-17 14:57 ` Frank Pagliughi
2015-03-17 15:19 ` Grant Edwards
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