worker signals and solo concurrency

[neg3ntropy]

4.4.0

worker_process_shutdown signal is not sent when a task is running with the solo pool. The solo pool is great for debugging, but it my case it makes the process hard to kill.

This is basically a rehash of #5405, but for another signal. It might make sense to generalize the solution to other relevant signals if any.

PS: Furthermore, it looks that the running task is left to finish and then the ACK fails, so it gets retried later.

[auvipy]

can you send a PR with fix and unit tests?

[neg3ntropy]

At least in the immediate future, no sorry, otherwise I would have done it.

[auvipy]

are you using the latest version of celery? and can you try celery from Github master?

[neg3ntropy]

still present in master

[auvipy]

please provide a failing testcase