unable to build v6.1.1 without pthreads.

[glennmcc]

root@glennmcc-i7:~/build/ffmpeg-6.1.1# ./configure --disable-pthreads

root@glennmcc-i7:~/build/ffmpeg-6.1.1# time make

Even tho I disabled pthreads.... it still got these errors and it did not build ffmpeg, ffprobe, ffplay for Linux.

In file included from libavcodec/vulkan.c:19:
./libavutil/vulkan.c: In function 'ff_vk_exec_pool_free':
./libavutil/vulkan.c:267:9: error: implicit declaration of function 'pthread_mutex_destroy'; did you mean 'ff_mutex_destroy'? [-Werror=implicit-function-declaration]
267 | pthread_mutex_destroy(&e->lock);
|
^{| ff_mutex_destroy
./libavutil/vulkan.c: In function 'ff_vk_exec_pool_init':
./libavutil/vulkan.c:410:15: error: implicit declaration of function 'pthread_mutex_init' [-Werror=implicit-function-declaration]
410 | err = pthread_mutex_init(&e->lock, NULL);
|} ~
./libavutil/vulkan.c: In function 'ff_vk_exec_wait':
./libavutil/vulkan.c:507:5: error: implicit declaration of function 'pthread_mutex_lock' [-Werror=implicit-function-declaration]
507 | pthread_mutex_lock(&e->lock);
| ^{~
./libavutil/vulkan.c:510:5: error: implicit declaration of function 'pthread_mutex_unlock'; did you mean 'ff_mutex_unlock'? [-Werror=implicit-function-declaration]
510 | pthread_mutex_unlock(&e->lock);
|} ~
| ff_mutex_unlock
cc1: some warnings being treated as errors
make: * [ffbuild/common.mak:81: libavcodec/vulkan.o] Error 1

[Gyan]

ffmpeg has required threading support since 760ce4bc0bd11f74f0851c0a662dd5cae888df83 (Jul 2022)

The vulkan make failure looks to be an oversight in the configure script but threading is required for vulkan as well.

[glennmcc]

For those questioning why I'm trying to build without threads.

This all came about while building newer versions of
both FFMPEG.EXE & FFPROBE.EXE for DOS using the DJGPP cross compiler
running on slackware Linux 64bit.

The following build script works perfectly for all the way up to v5.1.4

--- build-ffmpeg.sh ---

#!/bin/bash

# Set the DJGPP_PREFIX variable to the root directory of the DJGPP cross-compiler toolchain
export DJGPP_PREFIX="/archives-a/build/djgpp"
export PATH="$DJGPP_PREFIX/bin:$PATH"
export LIB="$DJGPP_PREFIX/lib/"
export GCC_EXEC_PREFIX="$DJGPP_PREFIX/lib/gcc/"
export INCLUDE="$DJGPP_PREFIX/include/"

# Define the target architecture by appending "/bin/i586-pc-msdosdjgpp" to the DJGPP_PREFIX
TARGET_ARCH="${DJGPP_PREFIX}/i586-pc-msdosdjgpp/bin/"

# Add the DJGPP_PREFIX/bin directory to the beginning of the PATH environment variable
export PATH="${DJGPP_PREFIX}/bin:$PATH"

# Define the version of FFmpeg to download
FFMPEG_VERSION="$1"

# Define the URL of the FFmpeg archive to download
FFMPEG_ARCHIVE="https://ffmpeg.org/releases/ffmpeg-${FFMPEG_VERSION}.tar.gz"

# Define the directory name where FFmpeg source will be extracted
FFMPEG_SOURCE_DIR="ffmpeg-${FFMPEG_VERSION}"

# Download the FFmpeg archive
wget -c "$FFMPEG_ARCHIVE"

# Remove any existing directory with the same name as FFMPEG_SOURCE_DIR
rm -rf "$FFMPEG_SOURCE_DIR"

# Extract the FFmpeg source from the downloaded archive
tar -xf "ffmpeg-${FFMPEG_VERSION}.tar.gz"

# Change the current directory to the FFmpeg source directory
cd $FFMPEG_SOURCE_DIR

# Run the configure script with specific options to prepare FFmpeg for cross-compilation
./configure \

--enable-cross-compile \
--cc="${TARGET_ARCH}gcc" \
--cxx="${TARGET_ARCH}g++" \
--ar="${TARGET_ARCH}ar" \
--as="${TARGET_ARCH}as" \
--ranlib="${TARGET_ARCH}ranlib" \
--sysroot="${DJGPP_PREFIX}" \
--disable-debug \
--arch=i486 \
--cpu=i486 \
--target-os=ms-dos \
--disable-doc \
--enable-gpl \
--disable-txtpages \
--extra-cflags="-w" \
--disable-pthreads \
--disable-vulkan

# Compile FFmpeg with multiple jobs, using the number of available processors
make -j$(nproc) 2>../1errors.txt

_

However, in the v6.x branch, even with that addition of --disable-vulkan,
as a result of Gyan pointing-out that vulkan requires threads,
only FFPROBE.EXE gets built and not FFMPEG.EXE

Therefore, there seem to be a whole bunch of items in the 6.x branch
that now require threads.

So for now, we old DOS diehards seem to be 'frozen' at v5.1.4

[Gyan]

Vulkan threads dep check added in 9e8be937fc4933ade00a18578f8c1420006d4291

ffmpeg threads dep won't be reverted.