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Date: Thu, 16 Feb 2012 13:06:37 -0800
From: Julian Elischer <julian@freebsd.org>
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To: Andriy Gapon <avg@freebsd.org>
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Cc: Alexander Kabaev <kan@freebsd.org>, threads@freebsd.org,
	FreeBSD Stable <freebsd-stable@freebsd.org>,
	Jens Axboe <jaxboe@fusionio.com>
Subject: Re: pthread_cond_timedwait() broken in 9-stable? (from JAN 10)
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On 2/16/12 9:34 AM, Andriy Gapon wrote:
> on 15/02/2012 23:41 Julian Elischer said the following:
>> The program fio (an IO test in ports) uses pthreads
>>
>> the following code (from fio-2.0.3, but its in earlier code too)
>> has suddenly started misbehaving.
>>
>>          clock_gettime(CLOCK_REALTIME,&t);
>>          t.tv_sec += seconds + 10;
>>
>>          pthread_mutex_lock(&mutex->lock);
>>
>>          while (!mutex->value&&  !ret) {
>>                  mutex->waiters++;
>>                  ret = pthread_cond_timedwait(&mutex->cond,&mutex->lock,&t);
>>                  mutex->waiters--;
>>          }
>>
>>          if (!ret) {
>>                  mutex->value--;
>>                  pthread_mutex_unlock(&mutex->lock);
>>          }
>>
>>
>> It turns out that 'ret' sometimes comes back instantly (on my machine) with a
>> value of 60 (ETIMEDOUT)
>> despite the fact that we set the timeout 10 seconds into the future.
>>
>> Has anyone else seen anything like this?
>> (and yes the condition variable attribute have been set to use the REALTIME clock).
> But why?
>
> Just a hypothesis that maybe there is some issue with time keeping on that system.
> How would that code work out for you with MONOTONIC?

Jens Axboe, (CC'd) tried both CLOCK_REALTIME and CLOCK_MONOTONIC, and 
they both had the same problem..
i.e. random early returns with ETIMEDOUT.

I think we will try move out machine forward to a newer -stable to see 
if it resolves.