[vlc-devel] [PATCH] HLS: don't signal dl thread out of the blue in Close()

Frederic YHUEL fyhuel at viotech.net
Thu Jun 28 13:08:44 CEST 2012

On Thu, Jun 28, 2012 at 12:22 PM, Rémi Denis-Courmont <remi at remlab.net> wrote:
> On Wed, 27 Jun 2012 20:55:15 +0200, Jean-Baptiste Kempf <jb at videolan.org>
> wrote:
>> I think some of those good advice should be on the wiki, on the
>> check-before-sending-for-review page.
> The VLC threading subsystem has (always) been modeled after POSIX threads.
> There is no point in writing duplicated sub-standard VLC-specific
> documentation for those generic C programming paradigms. Indeed, any
> programmer familiar with POSIX threads should be able to use VLC threads
> easily. Conversely, any programmer unfamiliar with threading can be
> referred to generic POSIX threads quality documentation (e.g. books), to
> learn to program not only for VLC but for many other C projects.
> Furthermore, reference to an external standard provides a sane
> specification for what the semantics should be. Some VLC-specific helper
> functions have been plagged with vague definitions and changing semantics
> across versions and developers (e.g. string processing): I want to avoid
> that problem whenever possible.

However, maybe it would be wise to warn people that some modules in
VLC don't use threads properly. For exemple, we can find the following
pattern in a few modules:

    vlc_mutex_lock( &w->cond  );
    vlc_cond_signal(&w->cond );
    vlc_mutex_unlock( &w->cond );

IOW, signaling "out of the blue", without modifying the condition
variable's predicate while the lock is held.


are such modules, where one can find this pattern.

Also, links with good documentation about threading could be nice,
IMHO. How to avoid deadlock? Wether to use fine-grained or
coarsed-grained locking? I think it's not that easy to find good
documentation about that subject.

Some articles like this one:
http://queue.acm.org/detail.cfm?id=2088916 are nice but also somewhat

> [WIth C11] to ensure data-race-freedom, it suffices to ensure that synchronization-free code sections that run at the same time don’t both write, or read and write, the same variables.

This is very cool. And with C99?

Best regards

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