On Tue, Oct 24, 2017 at 8:36 AM, James Almer <jamr...@gmail.com> wrote: > On 10/23/2017 10:24 PM, Michael Niedermayer wrote: >> On Tue, Oct 24, 2017 at 01:39:03AM +0100, Mark Thompson wrote: >>> On 24/10/17 00:52, Michael Niedermayer wrote: >>>> Hi >>>> >>>> On Mon, Oct 23, 2017 at 04:43:19PM +0100, Mark Thompson wrote: >>>>> On 23/10/17 03:56, Michael Niedermayer wrote: >>>>>> the initialization should be thread safe as it never writes a different >>>>>> value in the same spot >>>>> >>>>> This is not true; please be very careful with assumptions like this. >>>>> >>>>> The C standard calls this a data race and it is undefined behaviour. >>>> >>>> Thats interresting, we definitly do not want undefined behavior >>>> can you quote the relevant parts of the C standard >>>> which make writing the same value, a data race ? >>>> >>>> I was not aware of this if its true. >>>> Also i dont immedeatly see this in the "latest" draft i am looking at >>>> atm >>>> >>>> What i see is this: >>>> 4 Two expression evaluations conflict if one of them modifies a memory >>>> location and the >>>> other one reads or modifies the same memory location. >>>> ... >>>> 25 The execution of a program contains a data race if it contains two >>>> conflicting actions in >>>> different threads, at least one of which is not atomic, and neither >>>> happens before the >>>> other. Any such data race results in undefined behavior. >>>> >>>> This seems carefully worded to not include writing the same value. >>>> As "modification" implies change which does not occur when writing the >>>> same value. >>> >>> All writes are modifications. >>> >>> See section 3.1 note 2: >>> """ >>> 3 NOTE 2 "Modify"€™ includes the case where the new value being stored is >>> the same as the previous value. >>> """ >> >> That resolves the difference between our interpretation >> >> thanks > > Should i push this, or does someone want to give ff_thread_once() a try?
I've posted a patch. Thank's. _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
