Handler w/ flusher thread running in an event loop.

async_logging.py

import asyncio
import logging
import time
import threading
import typing as t

import janus

LOG = logging.getLogger(__name__)

# Queue must be created within the event loop it will be used from. Start as
# None since this will not be the main thread.
_QUEUE: t.Optional[janus.Queue] = None

class DBHandler(logging.Handler):
    def __init__(self, *args, **kwargs):
        # This is set from the flusher thread
        global _QUEUE
        while _QUEUE is None:
            time.sleep(0.01)
        self.q = _QUEUE.sync_q
        super().__init__(*args, **kwargs)

    def emit(self, record: logging.LogRecord):
        # Convert log record to row, and send to queue for insertion
        row = make_row(record)
        self.q.put(row)


def make_row(record: logging.LogRecord) -> "Row":
    # Use more columns than this
    return {"msg": record.message}


def flusher():
    async def run():
        global _QUEUE
        if _QUEUE is None:
            _QUEUE = janus.Queue()
        # Upload row instead of print. Perhaps flush every n-seconds w/ buffer
        # to have an upper-bound on inserts.
        q = _QUEUE.async_q
        while True:
            row = await q.get()
            print("woohoo, recived:", row["msg"])

    loop = asyncio.new_event_loop()
    asyncio.set_event_loop(loop)
    loop.run_until_complete(run())

threading.Thread(target=flusher, daemon=True).start()
LOG.setLevel(logging.INFO)
LOG.addHandler(DBHandler())

LOG.info("starting program")
LOG.info("doing some stuff")
LOG.info("mighty cool")
# woohoo, recived: starting program
# woohoo, recived: doing some stuff
# woohoo, recived: mighty cool