#!/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
+ """The pid of the process that holds the lock"""
+
commandline: str
+ """The commandline of the process that holds the lock"""
+
expiration_timestamp: Optional[float]
+ """When this lock will expire as seconds since Epoch"""
-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.
-
- with LockFile('./foo.lock'):
- # do a bunch of stuff... if the process dies we have a signal
- # handler to do cleanup. Other code (in this process or another)
- # that tries to take the same lockfile will block. There is also
- # some logic for detecting stale locks.
+ can use it in a with statement. e.g.::
+ with LockFile('./foo.lock'):
+ # do a bunch of stuff... if the process dies we have a signal
+ # handler to do cleanup. Other code (in this process or another)
+ # that tries to take the same lockfile will block. There is also
+ # some logic for detecting stale locks.
"""
def __init__(
expiration_timestamp: Optional[float] = None,
override_command: Optional[str] = None,
) -> None:
- self.is_locked = False
- self.lockfile = lockfile_path
- self.override_command = override_command
+ """C'tor.
+
+ Args:
+ lockfile_path: path of the lockfile to acquire
+ do_signal_cleanup: handle SIGINT and SIGTERM events by
+ releasing the lock before exiting
+ expiration_timestamp: when our lease on the lock should
+ expire (as seconds since the Epoch). None means the
+ lock will not expire until we explicltly release it.
+ override_command: don't use argv to determine our commandline
+ rather use this instead if provided.
+ """
+ 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)
self.expiration_timestamp = expiration_timestamp
def locked(self):
+ """Is it locked currently?"""
return self.is_locked
def available(self):
+ """Is it available currently?"""
return not os.path.exists(self.lockfile)
def try_acquire_lock_once(self) -> bool:
- logger.debug(f"Trying to acquire {self.lockfile}.")
+ """Attempt to acquire the lock with no blocking.
+
+ Returns:
+ True if the lock was acquired and False otherwise.
+ """
+ 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(
backoff_factor: float = 2.0,
max_attempts=5,
) -> bool:
+ """Attempt to acquire the lock repeatedly with retries and backoffs.
+
+ Args:
+ initial_delay: how long to wait before retrying the first time
+ backoff_factor: a float >= 1.0 the multiples the current retry
+ delay each subsequent time we attempt to acquire and fail
+ to do so.
+ max_attempts: maximum number of times to try before giving up
+ and failing.
+
+ Returns:
+ True if the lock was acquired and False otherwise.
+ """
+
@decorator_utils.retry_if_false(
tries=max_attempts, delay_sec=initial_delay, backoff=backoff_factor
)
return _try_acquire_lock_with_retries()
def release(self):
+ """Release the lock"""
try:
os.unlink(self.lockfile)
except Exception as e:
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_timestamp:
- msg = f'Lockfile {self.lockfile} expiration time has passed; force acquiring'
- logger.warning(msg)
+ 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.
projects / python_utils.git / blobdiff