| Context | Check | Description |
|---|---|---|
| andriy/x86 | warning | Failed to apply patch |
On Thu, Dec 3, 2020 at 1:36 AM Andreas Rheinhardt < andreas.rheinhardt@gmail.com> wrote: > av_cpu_count() intends to emit a debug message containing the number of > logical cores when called the first time. The check currently works with > a static volatile int; yet this does not help at all in case of > concurrent accesses by multiple threads. So replace this with an > atomic_int. > > Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com> > --- > To test my patches I have modified avcodec_open2() to always open the > desired AVCodecContext simultaneously from two different threads [1]. > With this one easily runs into this issue when one uses a decoder with > FF_CODEC_CAP_INIT_THREADSAFE that supports threading. > > [1]: https://pastebin.com/a1uEuQ81 > > libavutil/cpu.c | 6 ++---- > 1 file changed, 2 insertions(+), 4 deletions(-) > > diff --git a/libavutil/cpu.c b/libavutil/cpu.c > index 52f6b9a3bf..7b8a9045ab 100644 > --- a/libavutil/cpu.c > +++ b/libavutil/cpu.c > @@ -274,7 +274,7 @@ int av_parse_cpu_caps(unsigned *flags, const char *s) > > int av_cpu_count(void) > { > - static volatile int printed; > + static atomic_int printed = 0; > > int nb_cpus = 1; > #if HAVE_WINRT > @@ -306,10 +306,8 @@ int av_cpu_count(void) > nb_cpus = sysinfo.dwNumberOfProcessors; > #endif > > - if (!printed) { > + if (!atomic_exchange_explicit(&printed, 1, memory_order_relaxed)) > av_log(NULL, AV_LOG_DEBUG, "detected %d logical cores\n", > nb_cpus); > - printed = 1; > - } > > return nb_cpus; > } > -- > 2.25.1 > > Will apply. - Andreas
diff --git a/libavutil/cpu.c b/libavutil/cpu.c index 52f6b9a3bf..7b8a9045ab 100644 --- a/libavutil/cpu.c +++ b/libavutil/cpu.c @@ -274,7 +274,7 @@ int av_parse_cpu_caps(unsigned *flags, const char *s) int av_cpu_count(void) { - static volatile int printed; + static atomic_int printed = 0; int nb_cpus = 1; #if HAVE_WINRT @@ -306,10 +306,8 @@ int av_cpu_count(void) nb_cpus = sysinfo.dwNumberOfProcessors; #endif - if (!printed) { + if (!atomic_exchange_explicit(&printed, 1, memory_order_relaxed)) av_log(NULL, AV_LOG_DEBUG, "detected %d logical cores\n", nb_cpus); - printed = 1; - } return nb_cpus; }
av_cpu_count() intends to emit a debug message containing the number of logical cores when called the first time. The check currently works with a static volatile int; yet this does not help at all in case of concurrent accesses by multiple threads. So replace this with an atomic_int. Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com> --- To test my patches I have modified avcodec_open2() to always open the desired AVCodecContext simultaneously from two different threads [1]. With this one easily runs into this issue when one uses a decoder with FF_CODEC_CAP_INIT_THREADSAFE that supports threading. [1]: https://pastebin.com/a1uEuQ81 libavutil/cpu.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)