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make altinstall for PGO is not parallel-safe #93584
Description
Activity
My PR solved the race condition in
add_multiarch_paths()but revealed another race condition later.@pablogsal 's problem is caused by the fact that PGO builds use recursive make. The
sharedmodstarget and theprofile-opttarget run./python setup.py buildat the same time.setup.pyis not designed to be parallel-safe.Reacted by Emma SmithWeird, I never hit a compilation failure after 2 hours of trying on my 32 core machine, maybe this is an edge case you can only hit with the macOS scheduler.
Did you create a build with
configure --enable-optimizations? The issue only occurs with PGO builds.Yeah, I was running a script in a loop using the steps from Pablo's reproducer here: #84461 (comment)
After 2 hours it still hadn't failed
Yeah, I was running a script in a loop using the steps from Pablo's reproducer here: #84461 (comment)
After 2 hours it still hadn't failed
That's odd. I have been able to reproduce in at least 3 systems, including Linux with arch Linux and RHEL7
In comment #93589 (comment) @nascheme suggested to rename some of the targets to make the intention more clear. I like the idea, but I don't want to mix improvements with a release blocker fix.
- changed the title
[-]setup.py add_multiarch_paths() is not parallel-safe with recursive make[/-][+]make altinstall for PGO is not parallel-save[/+]on Jun 8, 2022 - changed the title
[-]make altinstall for PGO is not parallel-save[/-][+]make altinstall for PGO is not parallel-safe[/+]on Jun 15, 2022 @pablogsal As far as I know this bug has been fixed by GH-93589.
Reacted by Pablo Galindo Salgado- added a commit that references this issue
on Jun 26, 2022
Bug report
setup.pyhas a helper methodadd_multiarch_paths. The method creates a temporary filebuild/lib.{platform}/multiarchand unlinks it at the end of the function call. This is not parallel-safe.PGO builds of Python use
$(MAKE), so called recursive make. Recursive makes are considered harmful because the main make process has no understanding what the child make process is doing. With heavy parallel makes this can cause race conditions.The combination of unsafe
add_multiarch_paths(), recursive make and loooots of CPU cores can lead to build issues like #84461 (comment).Possible workarounds
$(MAKE)CC -print-multiarchanddpkg-architecture ... -qDEB_HOST_MULTIARCHcalls toconfigure.ac_bootsubprocess.check_output()andadd_multiarch_paths()to use a more safe tmp fileOption (3) is the simplest approach. Even
tmpfile = os.path.join(self.build_temp, f'multiarch-{os.getpid()}')would be good enough to avoid file conflicts in parallel builds.