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avutil/cpu: Fix race condition in av_cpu_count()

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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>
This commit is contained in:
Andreas Rheinhardt 2020-12-02 23:57:16 +01:00 committed by Andreas Rheinhardt
parent f38f791a23
commit a2a38b1606
1 changed files with 2 additions and 4 deletions
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6
libavutil/cpu.c
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@ -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 = ATOMIC_VAR_INIT(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;
}