#!/usr/bin/env python3
-from dataclasses import dataclass
+# © Copyright 2021-2022, Scott Gasch
+
+"""File-based locking helper."""
+
+from __future__ import annotations
+import contextlib
import datetime
import json
import logging
import os
import signal
import sys
-from typing import Optional
import warnings
+from dataclasses import dataclass
+from typing import Literal, Optional
import config
import datetime_utils
import decorator_utils
-
cfg = config.add_commandline_args(f'Lockfile ({__file__})', 'Args related to lockfiles')
cfg.add_argument(
'--lockfile_held_duration_warning_threshold_sec',
type=float,
- default=10.0,
+ default=60.0,
metavar='SECONDS',
help='If a lock is held for longer than this threshold we log a warning',
)
class LockFileException(Exception):
+ """An exception related to lock files."""
+
pass
@dataclass
class LockFileContents:
+ """The contents we'll write to each lock file."""
+
pid: int
commandline: str
- expiration_timestamp: float
+ expiration_timestamp: Optional[float]
-class LockFile(object):
+class LockFile(contextlib.AbstractContextManager):
"""A file locking mechanism that has context-manager support so you
can use it in a with statement. e.g.
expiration_timestamp: Optional[float] = None,
override_command: Optional[str] = None,
) -> None:
- self.is_locked = False
- self.lockfile = lockfile_path
- self.override_command = override_command
+ self.is_locked: bool = False
+ self.lockfile: str = lockfile_path
+ self.locktime: Optional[int] = None
+ self.override_command: Optional[str] = override_command
if do_signal_cleanup:
signal.signal(signal.SIGINT, self._signal)
signal.signal(signal.SIGTERM, self._signal)
return not os.path.exists(self.lockfile)
def try_acquire_lock_once(self) -> bool:
- logger.debug(f"Trying to acquire {self.lockfile}.")
+ logger.debug("Trying to acquire %s.", self.lockfile)
try:
# Attempt to create the lockfile. These flags cause
# os.open to raise an OSError if the file already
contents = self._get_lockfile_contents()
logger.debug(contents)
f.write(contents)
- logger.debug(f'Success; I own {self.lockfile}.')
+ logger.debug('Success; I own %s.', self.lockfile)
self.is_locked = True
return True
except OSError:
pass
- msg = f'Could not acquire {self.lockfile}.'
- logger.warning(msg)
+ logger.warning('Couldn\'t acquire %s.', self.lockfile)
return False
def acquire_with_retries(
logger.warning(msg)
raise LockFileException(msg)
- def __exit__(self, type, value, traceback):
+ def __exit__(self, _, value, traceback) -> Literal[False]:
if self.locktime:
ts = datetime.datetime.now().timestamp()
duration = ts - self.locktime
- if (
- duration
- >= config.config['lockfile_held_duration_warning_threshold_sec']
- ):
- str_duration = datetime_utils.describe_duration_briefly(duration)
+ if duration >= config.config['lockfile_held_duration_warning_threshold_sec']:
+ # Note: describe duration briefly only does 1s granularity...
+ str_duration = datetime_utils.describe_duration_briefly(int(duration))
msg = f'Held {self.lockfile} for {str_duration}'
logger.warning(msg)
warnings.warn(msg, stacklevel=2)
self.release()
+ return False
def __del__(self):
if self.is_locked:
line = lines[0]
line_dict = json.loads(line)
contents = LockFileContents(**line_dict)
- logger.debug(f'Blocking lock contents="{contents}"')
+ logger.debug('Blocking lock contents="%s"', contents)
# Does the PID exist still?
try:
os.kill(contents.pid, 0)
except OSError:
- msg = f'Lockfile {self.lockfile}\'s pid ({contents.pid}) is stale; force acquiring'
- logger.warning(msg)
+ logger.warning(
+ 'Lockfile %s\'s pid (%d) is stale; force acquiring...',
+ self.lockfile,
+ contents.pid,
+ )
self.release()
# Has the lock expiration expired?
if contents.expiration_timestamp is not None:
now = datetime.datetime.now().timestamp()
- if now > contents.expiration_datetime:
- msg = f'Lockfile {self.lockfile} expiration time has passed; force acquiring'
- logger.warning(msg)
+ if now > contents.expiration_timestamp:
+ logger.warning(
+ 'Lockfile %s\'s expiration time has passed; force acquiring',
+ self.lockfile,
+ )
self.release()
except Exception:
- pass
+ pass # If the lockfile doesn't exist or disappears, good.