On Fri, 23 Oct 2015 06:40:29 -0400 "Ronald S. Bultje" <rsbul...@gmail.com> wrote:
> Hi, > > On Fri, Oct 23, 2015 at 12:48 AM, Dale Curtis <dalecur...@chromium.org> > wrote: > > > On Wed, Oct 21, 2015 at 6:52 PM, Dale Curtis <dalecur...@chromium.org> > > wrote: > > > > > On Tue, Oct 20, 2015 at 11:50 PM, Michael Niedermayer < > > > mich...@niedermayer.cc> wrote: > > >> > > >> the last element to be written should be checked, so that if > > >> initialization is done by 2 threads at the same time, neither can > > >> return from this function without initialization having finished > > >> > > >> also the race detectors are broken if they complain about cases where > > >> a variable that has value a is set to value a, that cannot be part of > > >> a race, not even if a is written byte per byte instead of atomically > > >> unless theres something iam missing > > >> Is this something that can be fixed or disabled on the side of the > > >> race detectors? > > >> It might reduce false positives in FFmpeg and potentially other > > >> tools. > > >> > > > > > > We can suppress it, which I think is more reasonable then the overhead > > > it'd take to make this "race" go away. I notice the sin tables are > > > initialized within the fft context so there's no "race." Is there a > > reason > > > the cosine tables aren't done this way? > > > > > > > Actually it looks like sin may suffer from the same issues -- it doesn't > > make a copy like I was thinking it did. One of the TSAN folk detailed why > > suppression isn't a good idea here > > https://codereview.chromium.org/1412123007/#msg7 -- which roughly says we > > can't rely on the compiler to do the right thing here. > > > > What are your thoughts about using ff_thread_once() to build the full sin > > and cos tables all at once? > > > That sounds right. The reason that wasn't initially done is probably > because cos/sin tables existed before ff_thread_once did. Yep, it's a recent addition. We also want to stop the practice of initializing global tables without any form of synchronization. The existing codebase doesn't reflect how things should be done. There are 2 possibilities: 1. Using ff_thread_once() 2. Not using global tables, but moving them to per-instance contexts Both should be fine, but I think 2. is preferred. _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
