What happens if thread_id gets reused?

microsoft / mimalloc

mimalloc is a compact general purpose allocator with excellent performance.

MIT License

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What happens if thread_id gets reused? #956

Open malkia opened 3 weeks ago

malkia commented 3 weeks ago

Scenario:

Segment stores the thread_id it was created in.
The thread is no longer available, but the segment stays still keeping it's number.
After really long time, the thread_id gets reused, and as it happens the current thread has this number and wants to free object from the segment above (with the same thread_id)?

Does mimalloc handle this case gracefully?

daanx commented 2 weeks ago

Hi @malkia -- ah, no worries -- this is handled well. In particular, when a thread terminates the _mi_thread_done is called which will "abandon" all segments and set their thread-id to 0 (and preventing reused thread-id issues). Btw. we need to keep the segments alive since they contain still live data resulting from pointers that are shared with other threads). Later, other threads can "reclaim" such abandoned segments (see _mi_segment_try_reclaim) and reuse the memory that was abandoned.

malkia commented 2 weeks ago

Awesome - thank you so much! This makes it for another re-reading of the source code! Much appreciated!