[erlang-bugs] Supervisor terminate_child race

Tim Watson <>
Wed May 15 12:53:04 CEST 2013

On 15 May 2013, at 11:17, Robert Virding wrote:

> Do you mean only using monitors in the supervisor, and no links? If so that would not work as you would then not get an exit signal automatically sent to the child when the supervisor dies.
> Which you do want. Or have I misunderstood you?

Oh gosh, how embarrasing. I was thinking in terms of Uni-directional Links (viz A Unified Semantics for Future Erlang, Svensson et al), and linking child to parent (so as to propagate supervisor exits) but not the other way around. Of course we can't do that - just ignore this suggestion. [note: I've been implementing the supervisor API for cloud haskell in my spare time and got confused between those semantics (viz http://haskell-distributed.github.io/static/semantics.pdf) and what I do for a day job in the *real world*].

But switching all the supervisor's signal handling to rely on monitor notifications rather than trapped exits (which might be ignored) sounds good to me. The use of linking would be there to guarantee supervisor death is propagated correctly, but we could switch away from handling child 'EXIT' signals to handling 'DOWN' notifications instead. This would IMO be a bit cleaner.

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