aopen.py

# Asynchronous file open/close
# https://nullprogram.com/blog/2020/09/04/ 

import asyncio

class _AsyncOpen():
    def __init__(self, args, kwargs):
        self._args = args
        self._kwargs = kwargs

    def __aenter__(self):
        def thread_open():
            return open(*self._args, **self._kwargs)
        loop = asyncio.get_event_loop()
        self._future = loop.run_in_executor(None, thread_open)
        return self._future

    async def __aexit__(self, exc_type, exc, tb):
        file = await self._future
        def thread_close():
            file.close()
        loop = asyncio.get_event_loop()
        await loop.run_in_executor(None, thread_close)

def aopen(*args, **kwargs):
    return _AsyncOpen(args, kwargs)

## Test / demo

async def heartbeat():
    while True:
        await asyncio.sleep(0.5)
        print('HEARTBEAT')

async def write(i):
    async with aopen(f'/tmp/{i}', 'w') as out:
        print(i, file=out)

async def main():
    beat = asyncio.create_task(heartbeat())
    tasks = [asyncio.create_task(write(i)) for i in range(5)]
    await asyncio.gather(*tasks)
    beat.cancel()

asyncio.run(main())

open64.c

/* $ cc -shared -fPIC -o open64.so open64.c */
#define _GNU_SOURCE
#include <dlfcn.h>
#include <string.h>
#include <unistd.h>

int
open64(const char *path, int flags, int mode)
{
    if (!strncmp(path, "/tmp/", 5)) {
        sleep(3);
    }
    int (*orig)(const char *, int, int) = dlsym(RTLD_NEXT, "open64");
    return orig(path, flags, mode);
}