From: Yusuke ENDOH <mame@...>
Date: 2010-03-20T03:20:24+09:00
Subject: [ruby-core:28803] Re: [Bug #2629] ConditionVariable#wait(mutex, 	timeout) should return whether the condition was signalled, not the waited 	time

Hi,

2010/3/17 Yusuke Endoh <redmine@ruby-lang.org>:
> I could be wrong because I'm not familiar with multi-thread programming,
> but I doubt that it is potentially dangerous to depend on the reason of
> wait termination.  Couldn't it cause race condition?
>
> I have no idea about concrete race scenario, but there is a circumstance
> where Java's Object#wait seems not to return the termination reason.


I found ptherad_cond_timedwait returns ETIMEOUT.
My concern seemed to be needless fear.

But I still doubt a little whether your code has a race:

http://www.opengroup.org/onlinepubs/000095399/functions/pthread_cond_timedwait.html

> Similarly, when pthread_cond_timedwait() returns with the timeout error,
> the associated predicate may be true due to an unavoidable race between
> the expiration of the timeout and the predicate state change.
>
> The application needs to recheck the predicate on any return because it
> cannot be sure there is another thread waiting on the thread to handle
> the signal, and if there is not then the signal is lost. The burden is
> on the application to check the predicate.


And I realized a bigger problem from the document; it is considered as
a race to speficy a relative time as timeout.

ConditionVariable#wait should accept an absolute time, at least.
But it needs Mutex#sleep accept Time instead of Integer.  Umm.

-- 
Yusuke ENDOH <mame@tsg.ne.jp>