bpo-31356: Add context manager to temporarily disable GC by pablogsal · Pull Request #4224 · python/cpython (original) (raw)

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As far as thread-safety goes: the CM is just as thread-unsafe as doing this dance manually. That means if thread A enters first, then thread B enters, then thread A exits, the gc will be turned back on even though thread B is still inside the context manager.

While we could choose to make this more thread-safe by replacing the CM-local "Was the GC enabled?" flag with a process-global counted semaphore:

• that still isn't entirely thread-safe due to the possibility of direct calls to the underlying APIs
• it adds pointless overhead to the single-threaded case

What could be useful though is a "gc.isenabled()" check in exit that emits RuntimeWarning if the GC is already enabled at that point. That way, while the CM wouldn't magically fix your thread safety problems, it would help you find out you had them in the first place.