Speed-up CMake builds by allowing a persistent Cmake build dir #788
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When we build with
pip install -e . --no-build-isolation,cmakecurrently always relies onself.build_temp:https://github.com/pytorch/torchcodec/blob/de517c51f10f39d7d5e9a34714ecd00fece7ad36/setup.py#L129-L135
self.build_tempis automatically created at some point - not sure by what, whether it'spiporsetuptoolsor something else. It doesn't matter. What matters is that it's a temporary directory that changes for each invocation ofpip install -e . --no-build-isolation. And because it changes each time, it means the cmake configuration step is re-done each time as well. And that takes time.This PR adds a
TORCHCODEC_CMAKE_BUILD_DIRthat can be optionally specified to indicate a persistent build dir for cmake. This should greatly speed-up subsequent builds by avoiding the config step, and by avoiding re-compiling most files (but you should be using ccache anyway!!)I recommend doing something like
conda env config vars set TORCHCODEC_CMAKE_BUILD_DIR=${PWD}/buildwhere PWD is the torchcodec dir, so that this variable is set automatically when you activate your conda env.Here's a diff of the first and second
TORCHCODEC_CMAKE_BUILD_DIR=./build pip install -e . --no-build-isolationinvocations. Note the configuration step, and the lack of recompilation.