synapse-product/synapse/logging/handlers.py

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import logging
import time
from logging import Handler, LogRecord
from logging.handlers import MemoryHandler
from threading import Thread
from typing import Optional
from twisted.internet.interfaces import IReactorCore
class PeriodicallyFlushingMemoryHandler(MemoryHandler):
"""
This is a subclass of MemoryHandler that additionally spawns a background
thread to periodically flush the buffer.
This prevents messages from being buffered for too long.
Additionally, all messages will be immediately flushed if the reactor has
not yet been started.
"""
def __init__(
self,
capacity: int,
flushLevel: int = logging.ERROR,
target: Optional[Handler] = None,
flushOnClose: bool = True,
period: float = 5.0,
reactor: Optional[IReactorCore] = None,
) -> None:
"""
period: the period between automatic flushes
reactor: if specified, a custom reactor to use. If not specifies,
defaults to the globally-installed reactor.
Log entries will be flushed immediately until this reactor has
started.
"""
super().__init__(capacity, flushLevel, target, flushOnClose)
self._flush_period: float = period
self._active: bool = True
self._reactor_started = False
self._flushing_thread: Thread = Thread(
name="PeriodicallyFlushingMemoryHandler flushing thread",
target=self._flush_periodically,
daemon=True,
)
self._flushing_thread.start()
def on_reactor_running():
self._reactor_started = True
reactor_to_use: IReactorCore
if reactor is None:
from twisted.internet import reactor as global_reactor
reactor_to_use = global_reactor # type: ignore[assignment]
else:
reactor_to_use = reactor
# call our hook when the reactor start up
reactor_to_use.callWhenRunning(on_reactor_running)
def shouldFlush(self, record: LogRecord) -> bool:
"""
Before reactor start-up, log everything immediately.
Otherwise, fall back to original behaviour of waiting for the buffer to fill.
"""
if self._reactor_started:
return super().shouldFlush(record)
else:
return True
def _flush_periodically(self):
"""
Whilst this handler is active, flush the handler periodically.
"""
while self._active:
# flush is thread-safe; it acquires and releases the lock internally
self.flush()
time.sleep(self._flush_period)
def close(self) -> None:
self._active = False
super().close()