windows: use number of CPUs as automatic thread count

configure

@@ -1086,6 +1086,7 @@ HAVE_LIST="
     gethrtime
     GetProcessMemoryInfo
     GetProcessTimes
+    GetSystemInfo
     getrusage
     gnu_as
     ibm_asm
@@ -2859,6 +2860,7 @@ check_func_headers io.h setmode
 check_func_headers lzo/lzo1x.h lzo1x_999_compress
 check_lib2 "windows.h psapi.h" GetProcessMemoryInfo -lpsapi
 check_func_headers windows.h GetProcessTimes
+check_func_headers windows.h GetSystemInfo
 check_func_headers windows.h MapViewOfFile
 check_func_headers windows.h VirtualAlloc
 

libavcodec/pthread.c

@@ -34,6 +34,8 @@
 #if HAVE_SCHED_GETAFFINITY
 #define _GNU_SOURCE
 #include <sched.h>
+#elif HAVE_GETSYSTEMINFO
+#include <windows.h>
 #endif
 
 #include "avcodec.h"
@@ -156,6 +158,10 @@ static int get_logical_cpus(AVCodecContext *avctx)
     if (!ret) {
         nb_cpus = CPU_COUNT(&cpuset);
     }
+#elif HAVE_GETSYSTEMINFO
+    SYSTEM_INFO sysinfo;
+    GetSystemInfo(&sysinfo);
+    nb_cpus = sysinfo.dwNumberOfProcessors;
 #endif
     av_log(avctx, AV_LOG_DEBUG, "detected %d logical cores\n", nb_cpus);
     return FFMIN(nb_cpus, MAX_AUTO_THREADS);