[Issue 15939] GC.collect causes deadlock in multi-threaded environment

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=15939

--- Comment #18 from Martin Nowak <code at dawg.eu> ---
Think I just spotted the problem.

There seems to be a race condition between sending the signal and checking
whether the thread exited.
https://github.com/dlang/druntime/blob/c1f285715cf14e80307eafc76d0b25b417b8de19/src/core/thread.d#L2586-L2588
This might lead to a wrong counting of active threads, and therefor to a
deadlock.
https://github.com/dlang/druntime/blob/c1f285715cf14e80307eafc76d0b25b417b8de19/src/core/thread.d#L2648-L2649

Those changes were indeed introduced with
https://github.com/dlang/druntime/pull/1110.

A fix would be to simply synchronize the reception of the signal in
thread_suspendHandler with a variable in Thread, and only sem_wait for threads
that did receive the signal, somewhat similar to the FreeBSD workaround.

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