bpo-41273: asyncio's proactor read transport's better performance by using recv_into instead of recv

[tontinton]

https://bugs.python.org/issue41270

I got about 120% better performance on await reader.read() using this branch.

The way I tested was writing a server / client:
server.py:

importasyncioimportcontextlibimportdatetimeasyncdefclient_connected(reader, writer):
start=datetime.datetime.now()
withcontextlib.closing(writer):
foriinrange(100000):
awaitreader.read(1024*64) # tweak this parameter as much as you likediff=datetime.datetime.now() -startprint(f'{diff.seconds}.{diff.microseconds}')
asyncdefmain():
server=awaitasyncio.start_server(client_connected, '127.0.0.1', 8888)
addr=server.sockets[0].getsockname()
print(f'Serving on {addr}')
asyncwithserver:
awaitserver.serve_forever()
if__name__=="__main__":
asyncio.run(main())

client.py:

importasyncioimportcontextlibasyncdefflood(ip, port):
message=b'A'*1024*128# tweak this parameter as much as you likereader, writer=awaitasyncio.open_connection(ip, port)
withcontextlib.closing(writer):
whileTrue:
writer.write(message)
awaitwriter.drain()
if__name__=="__main__":
asyncio.run(flood('127.0.0.1', 8888))