wait_for(coro, timeout=0) memleak

[ixje]

BPO	37042
Nosy	@asvetlov, @1st1, @ixje
Files	test_leak_minimal.py: minimal example that bleeds memory test_leak_minimal_mem_consumption.png

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-05-25.12:09:54.889>
labels = ['expert-asyncio', '3.7', 'performance']
title = 'wait_for(coro, timeout=0) memleak'
updated_at = <Date 2019-05-25.12:34:53.128>
user = 'https://github.com/ixje'

bugs.python.org fields:

activity = <Date 2019-05-25.12:34:53.128>
actor = 'ixje'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['asyncio']
creation = <Date 2019-05-25.12:09:54.889>
creator = 'ixje'
dependencies = []
files = ['48356', '48357']
hgrepos = []
issue_num = 37042
keywords = []
message_count = 6.0
messages = ['343470', '343472', '343473', '343475', '343476', '343477']
nosy_count = 3.0
nosy_names = ['asvetlov', 'yselivanov', 'ixje']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'resource usage'
url = 'https://bugs.python.org/issue37042'
versions = ['Python 3.7']

[ixje]

I have a networked process that looks somewhat like this in its most basic form

import asyncio

shutting_down = False

async def read_message(reader, timeout=30):
    async def _read(reader: asyncio.StreamReader):
        try:
            d = await reader.readexactly(24)
            # do something with the data
            print("I'm never called")
        except:
            return None

    try:
        return await asyncio.wait_for(_read(reader), timeout)
    except Exception:
        return None


async def my_service():
    reader, writer = await asyncio.open_connection('127.0.0.1', 20333)
    while not shutting_down:
        m = await read_message(reader, timeout=0)
        if m is None:
            continue
        # else process message


if __name__ == "__main__":
    loop = asyncio.get_event_loop()
    loop.create_task(my_service())
    loop.run_forever()

read_message() has a default timeout of 30, but I thought setting it to 0 (instead of None) would be equal to blocking. This bleeds 16GB of memory in ~3 minutes. A minimal example is provided.

I manually applied the patch of https://bugs.python.org/issue36613 to a self compiled build of 3.7.3 (ef4ec6e) on Ubuntu 18.04 and that did not solve the problem.

[asvetlov]

Thanks for the report.
If the problem is in asyncio.wait_for() function the real network code can be stripped for the leakage example and replaced with await asyncio.sleep().

Would you try to boil down the snippet by converting it into a code that I can execute on my laptop to reproduce the problem?

[ixje]

Hi Andrew,
There is an attached minimal example (that differs from the code given in the first comment). I couldn't attach 2 files. So I pasted the code of one file to showcase how we could run into the issue, then a minimal reproducible example without network code in the attachment.

[asvetlov]

Nice, thanks!

[ixje]

This is the consumption I'm seeing.

[ixje]

Perhaps also worth mentioning is that when we supply None as timeout value in the wait_for() in the minimal sample, then it still reports 60MB memory usage. Seems pretty steep for doing basically nothing but looping around.

[kumaraditya303]

I am unable to reproduce the leak on main branch. I profiled with memray and the rss usage is constant.

[iritkatriel]

@kumaraditya303 were you able to reproduce it with 3.7?

[iritkatriel]

I tried myself - indeed I can reproduce it on 3.7 but no on main (on a MAC).