open-rmf/rmf_site freezes when updating from 1.5.1 to 1.5.3

[taiki-e]

Hello! I'm not sure whether it's a stack overflow but indeed our app was also broken when updating from 1.5.1 to 1.5.3. It's a complex app based on the Bevy game engine, where running it normally freezes, running it after locking the async-executor through cargo update -p async-executor --precise 1.5.1 works well.
It's a bit hard to understand what is happening and I don't want to bring in any red herring but bevy uses this executor to handle its tasks and it seems to get stuck in a sort of endless busy loop, without any significant memory leak but without any progress on the tasks it has assigned.

The app is here but I wouldn't really ask to run it and troubleshoot. Just thought I'd report the issue since we encountered it in a quite different package from the OP, so maybe it can shed some light.

Originally posted by @luca-della-vedova in #53 (comment)

[hymm]

Some bevy users have reported hanging here also. bevyengine/bevy#10032.

It's probably related to running nested executors, but I haven't have time to dig into it yet.

[notgull]

There is a busy loop mentioned; if you use a debugger to stop in the middle of this loop, what backtrack do you see? This would help us identify what part of the program is stuck in a loop.

[hymm]

There's a backtrace in the issue I linked above.

[notgull]

Nested executors have been a rough sticking point for a while now. I'd like to implement some code to simplify it so that nested executors aren't as much of a problem. The best solution would be to use the thread-local crate to reduce the number of workarounds we need, but I'm not sure that that crate's MSRV fits our policy. See Amanieu/thread_local-rs#62