Scheduling and signal delivery fixes #7822
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OTP-18838 When fetching signals for a process not in a running state and with parallel signal enqueue optimization enabled, it could end up being activated but not inserted into the run queue. If/when this happened the process would be stuck potentially for ever. Currently signals are only fetched for processes not in a running state when: a process that is receive traced is scheduled out, another process is inspected using process_info(Pid, message_queue_len), and in the break handler.
OTP-18839 When scheduling a process for dirty execution it could end up not being inserted into the run queue causing the process to get stuck for ever.
OTP-18841 Commit (1) changed so that signals sent to processes scheduled for dirty execution didn't trigger rescheduling of such processes to normal schedulers in order to handle signals, but instead rely on the dirty signal handler processes to take care of handling the signals for such processes. This since a steady flow of incoming signals to processes scheduled for dirty execution caused such processes to bounce between schedulers and could prevent them from making progress. The dirty signal handler processes did however not take care of the signals until the receiving processes were selected for execution. As a result of this, if a process got stuck for a long time in a dirty run queue due to heavy usage of dirty schedulers, it took a long time until signals were delivered to such processes. As of this commit, dirty signal handler processes will also take care of signal handling for processes in dirty run queues. (1) 53b1983
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Fixes #7801