As reported initially by @rad-pat in #6084, the following script causes a deadlock.
```
from concurrent.futures import ProcessPoolExecutor
class ObjectWithPickleError():
"""Triggers a RuntimeError when sending job to the workers"""
def __reduce__(self):
raise RuntimeError()
if __name__ == "__main__":
e = ProcessPoolExecutor()
f = e.submit(id, ObjectWithPickleError())
e.shutdown(wait=False)
f.result() # Deadlock on get
```
This is caused by the fact that the main process is closing communication channels that might be necessary to the `queue_management_thread` later. To avoid this, this PR let the `queue_management_thread` manage all the closing.
https://bugs.python.org/issue39104
Automerge-Triggered-By: @pitrou
Deprecated passing the following arguments as keyword arguments:
- "func" in functools.partialmethod(), weakref.finalize(),
profile.Profile.runcall(), cProfile.Profile.runcall(),
bdb.Bdb.runcall(), trace.Trace.runfunc() and
curses.wrapper().
- "function" in unittest.addModuleCleanup() and
unittest.TestCase.addCleanup().
- "fn" in the submit() method of concurrent.futures.ThreadPoolExecutor
and concurrent.futures.ProcessPoolExecutor.
- "callback" in contextlib.ExitStack.callback(),
contextlib.AsyncExitStack.callback() and
contextlib.AsyncExitStack.push_async_callback().
- "c" and "typeid" in the create() method of multiprocessing.managers.Server
and multiprocessing.managers.SharedMemoryServer.
- "obj" in weakref.finalize().
Also allowed to pass arbitrary keyword arguments (even "self" and "func")
if the above arguments are passed as positional argument.
ProcessPoolExecutor workers will hold the return value of their last task in memory until the next task is received. Since the return value has already been propagated to the parent process's Future (or has been discarded by this point), the object can be safely released.
Executors in concurrent.futures accepted tasks after executor was shutdown by interpreter exit. Tasks were left in PENDING state forever. This fix changes submit to instead raise a RuntimeError.
Fix deadlocks in :class:`concurrent.futures.ProcessPoolExecutor` when task arguments or results cause pickling or unpickling errors.
This should make sure that calls to the :class:`ProcessPoolExecutor` API always eventually return.
* bpo-31326: ProcessPoolExecutor waits for the call queue thread
concurrent.futures.ProcessPoolExecutor.shutdown() now explicitly
closes the call queue. Moreover, shutdown(wait=True) now also join
the call queue thread, to prevent leaking a dangling thread.
* Fix for shutdown() being called twice.
* bpo-27144: concurrent.futures as_complie and map iterators do not keep
reference to returned object
* Some nits. Improve wordings in docstrings and comments, and avoid relying on
sys.getrefcount() in tests.
Also, add a multiprocessing.connection.wait(rlist, timeout=None) function
for polling multiple objects at once. Patch by sbt.
Complete changelist from sbt's patch:
* Adds a wait(rlist, timeout=None) function for polling multiple
objects at once. On Unix this is just a wrapper for
select(rlist, [], [], timeout=None).
* Removes use of the SentinelReady exception and the sentinels argument
to certain methods. concurrent.futures.process has been changed to
use wait() instead of SentinelReady.
* Fixes bugs concerning PipeConnection.poll() and messages of zero
length.
* Fixes PipeListener.accept() to call ConnectNamedPipe() with
overlapped=True.
* Fixes Queue.empty() and SimpleQueue.empty() so that they are
threadsafe on Windows.
* Now PipeConnection.poll() and wait() will not modify the pipe except
possibly by consuming a zero length message. (Previously poll()
could consume a partial message.)
* All of multiprocesing's pipe related blocking functions/methods are
now interruptible by SIGINT on Windows.
Thomas Moreau
Kyle Stanley
ubordignon
Serhiy Storchaka
Brian Quinlan
Thomas Grainger
Dave Chevell
Mark Nemec
Antoine Pitrou
Victor Stinner
Grzegorz Grzywacz
Raymond Hettinger
Martin Panter
Antoine Pitrou
Richard Oudkerk
Ezio Melotti
Charles-François Natali
Andrew Svetlov
Mark Dickinson
Ross Lagerwall
Florent Xicluna
Martin v. Löwis
Georg Brandl