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:

import asyncio
import contextlib
import datetime


async def client_connected(reader, writer):
    start = datetime.datetime.now()

    with contextlib.closing(writer):
        for i in range(100000):
            await reader.read(1024 * 64)  # tweak this parameter as much as you like

    diff = datetime.datetime.now() - start
    print(f'{diff.seconds}.{diff.microseconds}')


async def main():
    server = await asyncio.start_server(client_connected, '127.0.0.1', 8888)

    addr = server.sockets[0].getsockname()
    print(f'Serving on {addr}')

    async with server:
        await server.serve_forever()


if __name__ == "__main__":
    asyncio.run(main())

client.py:

import asyncio
import contextlib


async def flood(ip, port):
    message = b'A' * 1024 * 128  # tweak this parameter as much as you like
    reader, writer = await asyncio.open_connection(ip, port)
    with contextlib.closing(writer):
        while True:
            writer.write(message)
            await writer.drain()


if __name__ == "__main__":
    asyncio.run(flood('127.0.0.1', 8888))