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Mini Shell
Mini Shell
"""holds locking functionality that works across processes"""
import logging
import os
from abc import ABCMeta, abstractmethod
from contextlib import contextmanager
from pathlib import Path
from threading import Lock, RLock
from filelock import FileLock, Timeout
class _CountedFileLock(FileLock):
def __init__(self, lock_file):
parent = os.path.dirname(lock_file)
if not os.path.isdir(parent):
try:
os.makedirs(parent)
except OSError:
pass
super().__init__(lock_file)
self.count = 0
self.thread_safe = RLock()
def acquire(self, timeout=None, poll_interval=0.05):
if not self.thread_safe.acquire(timeout=-1 if timeout is None else timeout):
raise Timeout(self.lock_file)
if self.count == 0:
super().acquire(timeout, poll_interval)
self.count += 1
def release(self, force=False):
with self.thread_safe:
if self.count > 0:
self.thread_safe.release()
if self.count == 1:
super().release(force=force)
self.count = max(self.count - 1, 0)
_lock_store = {}
_store_lock = Lock()
class PathLockBase(metaclass=ABCMeta):
def __init__(self, folder):
path = Path(folder)
self.path = path.resolve() if path.exists() else path
def __repr__(self):
return f"{self.__class__.__name__}({self.path})"
def __div__(self, other):
return type(self)(self.path / other)
def __truediv__(self, other):
return self.__div__(other)
@abstractmethod
def __enter__(self):
raise NotImplementedError
@abstractmethod
def __exit__(self, exc_type, exc_val, exc_tb):
raise NotImplementedError
@abstractmethod
@contextmanager
def lock_for_key(self, name, no_block=False):
raise NotImplementedError
@abstractmethod
@contextmanager
def non_reentrant_lock_for_key(self, name):
raise NotImplementedError
class ReentrantFileLock(PathLockBase):
def __init__(self, folder):
super().__init__(folder)
self._lock = None
def _create_lock(self, name=""):
lock_file = str(self.path / f"{name}.lock")
with _store_lock:
if lock_file not in _lock_store:
_lock_store[lock_file] = _CountedFileLock(lock_file)
return _lock_store[lock_file]
@staticmethod
def _del_lock(lock):
if lock is not None:
with _store_lock:
with lock.thread_safe:
if lock.count == 0:
_lock_store.pop(lock.lock_file, None)
def __del__(self):
self._del_lock(self._lock)
def __enter__(self):
self._lock = self._create_lock()
self._lock_file(self._lock)
def __exit__(self, exc_type, exc_val, exc_tb): # noqa: U100
self._release(self._lock)
self._del_lock(self._lock)
self._lock = None
def _lock_file(self, lock, no_block=False):
# multiple processes might be trying to get a first lock... so we cannot check if this directory exist without
# a lock, but that lock might then become expensive, and it's not clear where that lock should live.
# Instead here we just ignore if we fail to create the directory.
try:
os.makedirs(str(self.path))
except OSError:
pass
try:
lock.acquire(0.0001)
except Timeout:
if no_block:
raise
logging.debug("lock file %s present, will block until released", lock.lock_file)
lock.release() # release the acquire try from above
lock.acquire()
@staticmethod
def _release(lock):
lock.release()
@contextmanager
def lock_for_key(self, name, no_block=False):
lock = self._create_lock(name)
try:
try:
self._lock_file(lock, no_block)
yield
finally:
self._release(lock)
finally:
self._del_lock(lock)
lock = None
@contextmanager
def non_reentrant_lock_for_key(self, name):
with _CountedFileLock(str(self.path / f"{name}.lock")):
yield
class NoOpFileLock(PathLockBase):
def __enter__(self):
raise NotImplementedError
def __exit__(self, exc_type, exc_val, exc_tb): # noqa: U100
raise NotImplementedError
@contextmanager
def lock_for_key(self, name, no_block=False): # noqa: U100
yield
@contextmanager
def non_reentrant_lock_for_key(self, name): # noqa: U100
yield
__all__ = [
"NoOpFileLock",
"ReentrantFileLock",
"Timeout",
]
Zerion Mini Shell 1.0