[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 Windows and gcc run
time functions are available to get this information.  If available,
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 | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/libavutil/cpu.c b/libavutil/cpu.c
index f5785fc..a55921a 100644
--- a/libavutil/cpu.c
+++ b/libavutil/cpu.c
@@ -258,20 +258,25 @@ 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_GETPROCESSAFFINITYMASK, we will use Windows
+    // GetProcessAffinityMask() over gcc library function
+    // sched_getaffinity().  This avoids creating a dependency
+    // on the gcc thread library that we don't need/want.
+#if HAVE_GETPROCESSAFFINITYMASK
+    DWORD_PTR proc_aff, sys_aff;
+    if (GetProcessAffinityMask(GetCurrentProcess(), &proc_aff, &sys_aff))
+        nb_cpus = av_popcount64(proc_aff);
+#elif HAVE_SCHED_GETAFFINITY && defined(CPU_COUNT)
     cpu_set_t cpuset;
 
     CPU_ZERO(&cpuset);
 
     if (!sched_getaffinity(0, sizeof(cpuset), &cpuset))
         nb_cpus = CPU_COUNT(&cpuset);
-#elif HAVE_GETPROCESSAFFINITYMASK
-    DWORD_PTR proc_aff, sys_aff;
-    if (GetProcessAffinityMask(GetCurrentProcess(), &proc_aff, &sys_aff))
-        nb_cpus = av_popcount64(proc_aff);
 #elif HAVE_SYSCTL && defined(HW_NCPU)
     int mib[2] = { CTL_HW, HW_NCPU };
     size_t len = sizeof(nb_cpus);
@@ -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