Set multiprocessing.ProcessError with process exit-codes as the cause of the raised concurrent.futures.process.BrokenProcessPool¹ when a process in the process-pool is terminated (this BrokenProcessPool exception is raised in user-code on future.result(), for all current futures from the executor).

In addition, negative exit-codes are converted to their respective signals, as per the documentation.

¹ When the cause is None. When the cause is not None, then there is a failure to retrieve the process's return value or raised exception (eg broken pipe). If the process dies without putting anything on the result queue (such as seg-fault, os-kill, etc), then cause is None, and the only information to be retrieved is the process's exit-code

Implementation notes:

• concurrent.futures.process._ExecutorManagerThread.terminate_broken now accepts an exception instance instead of a list of strings
• concurrent.futures.process._ExecutorManagerThread.wait_result_broken_or_wakeup now returns an exception instance in the tuple's third element instead of a list of strings

https://bugs.python.org/issue41125