[FFmpeg-devel] [PATCH] Avoid creating unecessary dependencies on thread libraries.

[Gregory J. Wolfe]

(1) Multi-threading support requires knowing the number of CPUs available.
When building with MinGW on a Windows system, both gcc and Windows run
time functions are available to get this information.  However, when Windows
threading has been selected, the Windows function should be used, not the
gcc function.  This avoids creating an unnecessary dependency on the gcc
thread library.

(2) When ALL threading support is disabled, the build should not create a
dependency on ANY thread library.

Signed-off-by: Gregory J. Wolfe <gregory.wolfe at kodakalaris.com>
---
 libavutil/cpu.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/libavutil/cpu.c b/libavutil/cpu.c
index f5785fc..3843778 100644
--- a/libavutil/cpu.c
+++ b/libavutil/cpu.c
@@ -258,10 +258,15 @@ int av_cpu_count(void)
     static volatile int printed;
 
     int nb_cpus = 1;
+#if HAVE_THREADS
 #if HAVE_WINRT
     SYSTEM_INFO sysinfo;
 #endif
-#if HAVE_SCHED_GETAFFINITY && defined(CPU_COUNT)
+    // if HAVE_W32THREADS and HAVE_GETPROCESSAFFINITYMASK, we will use
+    // Windows GetProcessAffinityMask() instead of gcc library function
+    // sched_getaffinity().  This avoids creating a dependency on the gcc
+    // thread library that we don't need/want.
+#if HAVE_SCHED_GETAFFINITY && defined(CPU_COUNT) && !(HAVE_W32THREADS && HAVE_GETPROCESSAFFINITYMASK)
     cpu_set_t cpuset;
 
     CPU_ZERO(&cpuset);
@@ -286,6 +291,7 @@ int av_cpu_count(void)
     GetNativeSystemInfo(&sysinfo);
     nb_cpus = sysinfo.dwNumberOfProcessors;
 #endif
+#endif
 
     if (!printed) {
         av_log(NULL, AV_LOG_DEBUG, "detected %d logical cores\n", nb_cpus);
-- 
2.5.1.windows.1