Issue #12328: Fix multiprocessing's use of overlapped I/O on Windows.

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.

1 files changed, 4 insertions, 0 deletions

diff --git a/Misc/NEWS b/Misc/NEWS
index 52fd990..ef3d8c8 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -13,6 +13,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #12328: Fix multiprocessing's use of overlapped I/O on Windows.
+  Also, add a multiprocessing.connection.wait(rlist, timeout=None) function
+  for polling multiple objects at once.  Patch by sbt.
+
 - Issue #13719: Make the distutils and packaging upload commands aware of
   bdist_msi products.