build: remove pthread detection on Windows

[vtorri]

in CMakeLists.txt:

if(UNIX OR MINGW)
    # Find out if we have threading available
    set(THREADS_PREFER_PTHREAD_FLAG ON)
    find_package(Threads)
    target_link_libraries(avif_obj PRIVATE m Threads::Threads)
endif()

but in reformat.c (only file where pthread is used), the windows code uses native thread API

maybe one should use if (UNIX) only ?

[wantehchang]

Hi vtorri,

I am not familiar with the CMake Threads::Threads package, but the CMake FindThreads documentation does not say it is pthreads only. For example, it mentions three threading libraries:

• CMAKE_USE_WIN32_THREADS_INIT
• CMAKE_USE_PTHREADS_INIT
• CMAKE_HP_PTHREADS_INIT. Note: If I understand it correctly, this refers to the DCE threads in very old versions of HP-UX and is obsolete now.

So the code snippet in CMakeLists.txt that you quoted seems fine and is essentially the sams as the the CMake FindThreads example code. In fact I think we can remove the if(UNIX OR MINGW) check.

[vtorri]

i would keep if (UNIX) as mingw ships winpthread lib. pthread check is useless on Windows

[kmilos]

i would keep if (UNIX) as mingw ships winpthread lib

Which is why if(UNIX OR MINGW) is/was there, UNIX is not defined for MinGW.

However, it really does look like not even winpthreads is used for MinGW (MSYS2) builds:

$ ntldd libavif-16.dll
        KERNEL32.dll => C:\WINDOWS\SYSTEM32\KERNEL32.dll (0x000002189c390000)
        libaom.dll (0x000002189d430000)
        libdav1d-7.dll (0x000002189c390000)
        librav1e.dll (0x000002189c390000)
        libsharpyuv-0.dll (0x000002189c2b0000)
        libSvtAv1Enc-4.dll (0x000002189d430000)
        libyuv.dll (0x000002189c390000)

[vtorri]

it's normal, as win32 native threads are used on Windows, afaics

[kmilos]

Yep, just saying removing MINGW is an option after all, as winpthreads are not actually used.

[wantehchang]

Please review PR #3271. It makes two changes:

• Prefer pthread only on Unix because libavif uses Win32 native threads on Windows (including MinGW).
• Call find_package(Threads) on all platforms;.