gh-90622: Prevent concurrent.futures.process deadlock due to fork() after spawning a thread.#30847
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gpshead wants to merge 4 commits intopython:mainfrom
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gh-90622: Prevent concurrent.futures.process deadlock due to fork() after spawning a thread.#30847gpshead wants to merge 4 commits intopython:mainfrom
gpshead wants to merge 4 commits intopython:mainfrom
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…thonGH-27373)" This reverts commit fdc0e09. This implementation relies on a mechanism for spawning new children dynamically rather than up front that leads to deadlocks due to mixing of threads+fork. See bpo-46464.
bpo-39207: Spawn workers on demand in ProcessPoolExecutor (pythonGH-19453) was implemented in a way that introduced child process deadlocks in some environments due to mixing threading and fork() in the parent process.
gpshead
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See bug discussion. It looks like this will split into 2 and the max_tasks_per_child feature can be kept so long as it becomes an error when a 'fork' mp_context would be used. |
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1ac6e37 released in 3.9 as a performance enhancement to
concurrent.futuresintroduced a deadlock in some environments by violating the POSIX spec with new child processes being fork()ed after a thread had been started. This reverts that. It also reverts fdc0e09 which tried to add a newmax_tasks_per_child featurefor 3.11 that built upon the previous ill fated 3.9 performance enhancement.There is a better way to do this that would not fork after starting a thread, but implementing that is a much larger architectural enhancement; not something that could be back-ported as a bug fix.
The 3.10 backport will need to be manual as it doesn't have the 3.11 change. The 3.9 one can be autogenerated from that. Alternatively I could split this PR into two separate rollbacks.
https://bugs.python.org/issue46464