[vlc-devel] [PATCH 1/7] playlist/background_worker: introduce background-worker utility

[Filip Roséen]

Hi Rémi,

On 2017-03-29 22:26, Rémi Denis-Courmont wrote:

> Le keskiviikkona 29. maaliskuuta 2017, 21.20.02 EEST Filip Roséen a écrit :
> > On 2017-03-29 22:03, Rémi Denis-Courmont wrote:
> > > Le keskiviikkona 29. maaliskuuta 2017, 20.50.50 EEST Filip Roséen a écrit 
> :
> > > > > > The thread is per definition not waiting for the conditiona variable
> > > > > > at that time, so I cannot see how it would wake itself up.
> > > > > 
> > > > > You are making unwarranted assumptions about condition variables here.
> > > > 
> > > > Assumptions based on specifications, I would however be extremely
> > > > interested on implimentations where this "assumption" does not hold
> > > > (mostly because a issue should definitely be filed based on such
> > > > finding).
> > > > 
> > > > > Been there done that.
> > > > 
> > > > Previous paragraph.
> > > 
> > > There is not much point in discussing if we cannot agree on facts such as
> > > the meaning of the specification.
> > 
> > Opinion acknowledged.
> > 
> > > Both my experience and my understanding of CV tells me that this patch is
> > > factually wrong.
> > 
> > Given that you say that my assumptions are wrong, the code should be
> > easy to break, or there should be a very easy way to demonstrate that
> > my assumptions about *condition-variables* are wrong.
> > 
> > I am happy to take a conforming implementation of the specification as
> > an example, so if you could be kind to link me the source of such I
> > would happily read it.
> 
> I already told you: the thread can end up waking itself up, instead of the 
> more intuitive behaviour that you expect.
> 
> In other words, it is perfectly possible for: lock; signal/broadcast; wait; 
> unlock; to steal the wake up, when you would expect that it wakes up another 
> thread (if any is sleeping).
> 
> You could argue that many a description of condition variable rules such 
> behaviour out, or at least seems to. But this happens in real life, and I 
> cannot say that it would contradict the "original" POSIX definition.

I have not seen a single implementation that would allow for such
behavior, but I am interested in one that does. Also, since you are so
keen on the waking up itself part, spurious wake-ups are allowed and
expected, so how would this **actually** lead to any strange (besides
potentially unwanted) behavior?
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