On Mon, 21 Nov 2016 16:23:03 +0000 Gregory J Wolfe <gregory.wo...@kodakalaris.com> wrote:
> > -----Original Message----- > > From: ffmpeg-devel [mailto:ffmpeg-devel-boun...@ffmpeg.org] On > > Behalf Of wm4 > > Sent: Monday, November 21, 2016 10:05 AM > > To: ffmpeg-devel@ffmpeg.org > > Subject: Re: [FFmpeg-devel] [PATCH] Avoid creating unecessary > > dependencies on thread libraries. > > > > On Mon, 21 Nov 2016 09:58:33 -0500 > > "Gregory J. Wolfe" <gregory.wo...@kodakalaris.com> wrote: > > > > > (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.wo...@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); > > > > Wouldn't it be better to move the HAVE_GETPROCESSAFFINITYMASK > > case > > above HAVE_SCHED_GETAFFINITY, and avoid making the ifdeffery > > mess > > worse? GetProcessAffinityMask is available on every supported > > Windows > > and could as well be replaced by "ifdef _WIN32" instead. > > > > Yeah, I had the same thought. For the first go around I opted for the > solution that moved around the least code, not knowing for sure if > I might cause some undesirable side effects by reordering the existing > code. I can easily redo the patch if we're in agreement on this point. Depends if there are any cargo cult people who are against it. > > Also, technically you might have to stop the configure script to stop > > linking to libpthread. I'm not sure what exactly stops it from doing > > that in your case. > > The result I observed was that the resulting avutil.dll did NOT have > a dependency on the gcc run time. My interpretation of this is that > if you link against a library, but don't reference any symbols in it, then > it's as if you never linked against it in the first place. This could still be caused by certain link flag (forgot which one). In general, linking against a dynamic library without using any of its functions, could still have side effects, such as registering plugins in the DLL init functions and such. _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
