Async write to stdout slower than print?

Source

While implementing HTTP benchmarking tool with asyncio, I was playing with asyncronous writes to stdout - aka async print. My motivation was to improve performance of course :).

But after running some small benchmarks:

import asyncio
import os
import time

async def make_stdout(loop):
    writer_transport, writer_protocol = await loop.connect_write_pipe(
        FlowControlMixin, os.fdopen(1, 'wb'))
    return asyncio.StreamWriter(writer_transport, writer_protocol, None, loop)

async def do_async_print(loop):
    stdout = await make_stdout(loop)
    started = time.time()
    for _ in range(4000):
        stdout.write(b'works works works works works works works works works works\n')
    stdout.write(bytes('Time taken: {}'.format(time.time() - started), 'ascii'))

def test_async_print():
    loop = asyncio.get_event_loop()
    loop.run_until_complete(do_async_print(loop))
    loop.close()

def test_sync_print():
    started = time.time()
    for _ in range(4000):
        print('works works works works works works works works works works')
    print('Time taken:', time.time() - started)

Turns out that test_sync_print() runs quite faster than test_async_print(). In average 4000 sync prints run in 100 ms, whereas async print in 150 ms.

Also, if I go beyond 4000 prints asynchronous method blocks for unknown reasons. Synchronous works as expected.

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