Supporting out-of-band buffers (pickle protocol 5) in multiprocessing

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-09-27.19:04:19.301>
labels = ['3.8', '3.9', 'expert-IO', 'performance', '3.11', 'library', '3.10']
title = 'Supporting out-of-band buffers (pickle protocol 5) in multiprocessing'
updated_at = <Date 2021-09-27.19:04:19.301>
user = 'https://github.com/jakirkham'

bugs.python.org fields:

activity = <Date 2021-09-27.19:04:19.301>
actor = 'jakirkham'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)', 'IO']
creation = <Date 2021-09-27.19:04:19.301>
creator = 'jakirkham'
dependencies = []
files = []
hgrepos = []
issue_num = 45304
keywords = []
message_count = 1.0
messages = ['402736']
nosy_count = 1.0
nosy_names = ['jakirkham']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue45304'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10', 'Python 3.11']