public inbox for
 help / color / mirror / Atom feed
From: Frank Pagliughi <>
To: Grant Edwards <>,
Subject: Re: [ECOS] Re: Once again, I need a binary semaphore
Date: Tue, 17 Mar 2015 14:57:00 -0000	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <me9epm$e2m$>

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?


On 03/17/2015 10:47 AM, Grant Edwards wrote:
> On 2015-03-17, Grant Edwards <> wrote:
>> On 2015-03-17, lesc <> 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).

Before posting, please read the FAQ:
and search the list archive:

  reply	other threads:[~2015-03-17 14:57 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
2015-03-17 14:57       ` Frank Pagliughi [this message]
2015-03-17 15:19         ` Grant Edwards

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).