This is the mail archive of the
ecos-discuss@sourceware.org
mailing list for the eCos project.
Re: Once again, I need a binary semaphore
- From: Grant Edwards <grant dot b dot edwards at gmail dot com>
- To: ecos-discuss at ecos dot sourceware dot org
- Date: Tue, 17 Mar 2015 14:32:26 +0000 (UTC)
- Subject: Re: Once again, I need a binary semaphore
- Authentication-results: sourceware.org; auth=none
- References: <me737v$ojs$1 at ger dot gmane dot org> <5507F21B dot 1000900 at zhaw dot ch>
On 2015-03-17, lesc <lesc@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.
I'm not sure why a counting semaphore wasn't used by the applications
author. I haven't analyzed all of the possible execution paths, but
the original author of the application very specifically chose to use
a binary semaphore instead of a counting semaphore, and it seemed
wisest not to change things without a good reason. It took a
half-hour to implement a C API for binary semaphores, it could take
weeks to analyze tens of thousands lines of third-party code to see if
a counting semaphore would work the same as a binary semaphore in all
the corner cases.
--
Grant Edwards grant.b.edwards Yow! I guess you guys got
at BIG MUSCLES from doing too
gmail.com much STUDYING!
--
Before posting, please read the FAQ: http://ecos.sourceware.org/fom/ecos
and search the list archive: http://ecos.sourceware.org/ml/ecos-discuss