#!/usr/bin/env python3
-from dataclasses import dataclass
+"""File-based locking helper."""
+
import datetime
import json
import logging
import os
import signal
import sys
+import warnings
+from dataclasses import dataclass
from typing import 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=60.0,
+ metavar='SECONDS',
+ help='If a lock is held for longer than this threshold we log a warning',
+)
logger = logging.getLogger(__name__)
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):
"""A file locking mechanism that has context-manager support so you
- can use it in a with statement.
+ 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__(
- self,
- lockfile_path: str,
- *,
- do_signal_cleanup: bool = True,
- expiration_timestamp: Optional[float] = None,
- override_command: Optional[str] = None,
+ self,
+ lockfile_path: str,
+ *,
+ do_signal_cleanup: bool = True,
+ 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
- logger.debug(f'Failed; I could not acquire {self.lockfile}.')
+ logger.warning('Couldn\'t acquire %s.', self.lockfile)
return False
def acquire_with_retries(
- self,
- *,
- initial_delay: float = 1.0,
- backoff_factor: float = 2.0,
- max_attempts = 5
+ self,
+ *,
+ initial_delay: float = 1.0,
+ backoff_factor: float = 2.0,
+ max_attempts=5,
) -> bool:
-
- @decorator_utils.retry_if_false(tries = max_attempts,
- delay_sec = initial_delay,
- backoff = backoff_factor)
+ @decorator_utils.retry_if_false(
+ tries=max_attempts, delay_sec=initial_delay, backoff=backoff_factor
+ )
def _try_acquire_lock_with_retries() -> bool:
success = self.try_acquire_lock_once()
if not success and os.path.exists(self.lockfile):
def __enter__(self):
if self.acquire_with_retries():
+ self.locktime = datetime.datetime.now().timestamp()
return self
msg = f"Couldn't acquire {self.lockfile}; giving up."
logger.warning(msg)
raise LockFileException(msg)
- def __exit__(self, type, value, traceback):
+ def __exit__(self, _, value, traceback):
+ 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)
+ msg = f'Held {self.lockfile} for {str_duration}'
+ logger.warning(msg)
+ warnings.warn(msg, stacklevel=2)
self.release()
def __del__(self):
cmd = self.override_command
else:
cmd = ' '.join(sys.argv)
- print(cmd)
contents = LockFileContents(
- pid = os.getpid(),
- commandline = cmd,
- expiration_timestamp = self.expiration_timestamp,
+ pid=os.getpid(),
+ commandline=cmd,
+ expiration_timestamp=self.expiration_timestamp,
)
return json.dumps(contents.__dict__)
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:
- logger.debug('The pid seems stale; killing the lock.')
+ msg = f'Lockfile {self.lockfile}\'s pid ({contents.pid}) is stale; force acquiring'
+ logger.warning(msg)
self.release()
# Has the lock expiration expired?
if contents.expiration_timestamp is not None:
now = datetime.datetime.now().timestamp()
- if now > contents.expiration_datetime:
- logger.debug('The expiration time has passed; ' +
- 'killing the lock')
+ if now > contents.expiration_timestamp:
+ msg = f'Lockfile {self.lockfile} expiration time has passed; force acquiring'
+ logger.warning(msg)
self.release()
except Exception:
pass
projects / python_utils.git / blobdiff