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Re: pthread mutex used like a semaphore. Why does it work?

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On Mon, 19 May 2014 09:12:08 +0100, Richard Kettlewell wrote:

> "Charles T. Smith" <cts.private.yahoo@gmail.com> writes:
>> I'm looking at a piece of code where one thread locks a mutex at
>> regular intervals and a different thread frees that lock.  I thought it
>> was an error for a different thread to free a mutex, but it seems to be
>> working and there's no error code.
>>
>> I see the following at http://pubs.opengroup.org/onlinepubs/9699919799/
>> functions/pthread_mutex_lock.html:
>>
>> The pthread_mutex_unlock() function shall fail if:
>>
>>   [EPERM]
>>     The mutex type is PTHREAD_MUTEX_ERRORCHECK or
>>     PTHREAD_MUTEX_RECURSIVE,
>> or the mutex is a robust mutex, and the current thread does not own the
>> mutex.
>>
>>
>> How does a PTHREAD_MUTEX_DEFAULT mutex react if a non-owning thread
>> unlocks it?
> 
> There’s a table at the top of the page which gives the behavior for the
> various cases.


Yes, you're right.
	Mutex Type	Robustness	Relock	Unlock When Not Owner
	NORMAL		non-robust	deadlock undefined behavior

Before I file that as a bug report, I just wanted to be sure that nobody 
would say that "everybody knows that a mutex unlocked by another thread 
is obviously a perfectly good semaphore"!

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Thread

pthread mutex used like a semaphore.  Why does it work? "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2014-05-18 18:51 +0000
  Re: pthread mutex used like a semaphore.  Why does it work? "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2014-05-18 19:26 +0000
  Re: pthread mutex used like a semaphore.  Why does it work? Xavier Roche <xroche@free.fr.NOSPAM.invalid> - 2014-05-19 08:32 +0200
    Re: pthread mutex used like a semaphore.  Why does it work? "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2014-05-19 08:16 +0000
  Re: pthread mutex used like a semaphore.  Why does it work? Richard Kettlewell <rjk@greenend.org.uk> - 2014-05-19 09:12 +0100
    Re: pthread mutex used like a semaphore.  Why does it work? "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2014-05-19 08:27 +0000
  Re: pthread mutex used like a semaphore.  Why does it work? Mark <i@dontgetlotsofspamanymore.invalid> - 2014-05-19 10:50 +0100
  Re: pthread mutex used like a semaphore.  Why does it work? Chick Tower <c.tower@deadspam.com> - 2014-05-19 19:16 +0000
    Re: pthread mutex used like a semaphore.  Why does it work? "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2014-05-20 10:24 +0000
      Re: pthread mutex used like a semaphore.  Why does it work? David Brown <david.brown@hesbynett.no> - 2014-05-20 21:27 +0200
      Re: pthread mutex used like a semaphore.  Why does it work? Chick Tower <c.tower@deadspam.com> - 2014-05-21 02:22 +0000
    Re: pthread mutex used like a semaphore.  Why does it work? Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2014-05-20 22:33 -0400
  Re: pthread mutex used like a semaphore.  Why does it work? James Moe <jimoeDESPAM@sohnen-moe.com> - 2014-05-20 11:13 -0700
    Re: pthread mutex used like a semaphore.  Why does it work? "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2014-05-20 19:39 +0000
      Re: pthread mutex used like a semaphore.  Why does it work? Mark <i@dontgetlotsofspamanymore.invalid> - 2014-05-22 08:59 +0100

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