State corruption with multiple tasks running on same directory · mesonbuild/meson#2922

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Description

I ran ninja -C build after changing some options. At the middle, or towards the end, I hit ^Z to check on something. After checking, I totally forgot that the job was already running, and started it again. Realizing I had done that, I killed the new job, and resumed the old one. I got:

$ nice ninja -j4 -C armv7-build 
ninja: Entering directory `armv7-build'
[0/1] Regenerating build files.
Error during basic setup:

Something went terribly wrong. Please file a bug.
FAILED: build.ninja 
/usr/bin/python3.6 /home/ilia/src/meson/meson.py --internal regenerate /home/ilia/src/mesa-meson /home/ilia/src/mesa-meson/armv7-build --backend ninja
ninja: error: rebuilding 'build.ninja': subcommand failed

Do I now have to wipe the whole build directory and all the things that were already built in it?

Contributor guide

Tech stack: python
Domain: build system
Issue type: bug
Difficulty: 4
Estimated time: 3-5 days
Activity status: stale
Clarity: clear
Prerequisites: Understanding of Meson build systemBasics of file locking and concurrency
Newbie friendliness: 20
Research direction: The issue describes state corruption when two meson builds run concurrently in the same directory. Investigate file locking mechanisms used by Meson and Ninja, particularly around the build.ninja file and other intermediate files. Look at how Meson handles concurrent access and if there is any atomicity in file operations. Consider suggesting a lock file or a warning when a build directory is already in use. Review the Meson source code in mesonbuild/meson for relevant files like mesonbuild/mesonmain.py, backends/ninjabackend.py, and any state files.