I'm in agreement, for what it's worth. I've had to make use of the
binary semaphore through the C++ API, and it always made me wonder why
it wasn't brought out to the public/C API. Why code up the exact same
thing with a condition variable when there's a perfectly good binary
semaphore in the OS?
Frank
On 03/17/2015 10:47 AM, Grant Edwards wrote:
On 2015-03-17, Grant Edwards <grant.b.edwa...@gmail.com> wrote:
On 2015-03-17, lesc <l...@zhaw.ch> 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
sync-mechanism).
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).
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