fix potential hang.
It can happen that the child crashes right in the beginning for whatever reason. In this case, the parent will hang when writing into the pipe, because the child fd is not closed yet.
The normal pattern is to close the child fds right after the child proc is forked/executed/spawned, so when the child dies, then also the pipes will be closed, and there will be no hang (the parent gets SIGPIPE instead).
The multiprocessing.resource_tracker replaces the multiprocessing.semaphore_tracker module. Other than semaphores, resource_tracker also tracks shared_memory segments. Patch by Pierre Glaser.
* Fix bpo-30596: Add close() method to multiprocessing.Process
* Raise ValueError if close() is called before the Process is finished running
* Add docs
* Add NEWS blurb
