Source code for portalocker.utils

import os
import time
import atexit
import tempfile
import contextlib
from . import exceptions
from . import constants
from . import portalocker

current_time = getattr(time, "monotonic", time.time)

DEFAULT_TIMEOUT = 5
DEFAULT_CHECK_INTERVAL = 0.25
LOCK_METHOD = constants.LOCK_EX | constants.LOCK_NB

__all__ = [
    'Lock',
    'open_atomic',
]


[docs]@contextlib.contextmanager def open_atomic(filename, binary=True): '''Open a file for atomic writing. Instead of locking this method allows you to write the entire file and move it to the actual location. Note that this makes the assumption that a rename is atomic on your platform which is generally the case but not a guarantee. http://docs.python.org/library/os.html#os.rename >>> filename = 'test_file.txt' >>> if os.path.exists(filename): ... os.remove(filename) >>> with open_atomic(filename) as fh: ... written = fh.write(b'test') >>> assert os.path.exists(filename) >>> os.remove(filename) ''' assert not os.path.exists(filename), '%r exists' % filename path, name = os.path.split(filename) # Create the parent directory if it doesn't exist if path and not os.path.isdir(path): # pragma: no cover os.makedirs(path) temp_fh = tempfile.NamedTemporaryFile( mode=binary and 'wb' or 'w', dir=path, delete=False, ) yield temp_fh temp_fh.flush() os.fsync(temp_fh.fileno()) temp_fh.close() try: os.rename(temp_fh.name, filename) finally: try: os.remove(temp_fh.name) except Exception: pass
[docs]class Lock(object): def __init__( self, filename, mode='a', timeout=DEFAULT_TIMEOUT, check_interval=DEFAULT_CHECK_INTERVAL, fail_when_locked=False, flags=LOCK_METHOD): '''Lock manager with build-in timeout filename -- filename mode -- the open mode, 'a' or 'ab' should be used for writing truncate -- use truncate to emulate 'w' mode, None is disabled, 0 is truncate to 0 bytes timeout -- timeout when trying to acquire a lock check_interval -- check interval while waiting fail_when_locked -- after the initial lock failed, return an error or lock the file fail_when_locked is useful when multiple threads/processes can race when creating a file. If set to true than the system will wait till the lock was acquired and then return an AlreadyLocked exception. Note that the file is opened first and locked later. So using 'w' as mode will result in truncate _BEFORE_ the lock is checked. ''' if 'w' in mode: truncate = True mode = mode.replace('w', 'a') else: truncate = False self.fh = None self.filename = filename self.mode = mode self.truncate = truncate self.timeout = timeout self.check_interval = check_interval self.fail_when_locked = fail_when_locked self.flags = flags
[docs] def acquire( self, timeout=None, check_interval=None, fail_when_locked=None): '''Acquire the locked filehandle''' if timeout is None: timeout = self.timeout if timeout is None: timeout = 0 if check_interval is None: check_interval = self.check_interval if fail_when_locked is None: fail_when_locked = self.fail_when_locked # If we already have a filehandle, return it fh = self.fh if fh: return fh # Get a new filehandler fh = self._get_fh() try: # Try to lock fh = self._get_lock(fh) except exceptions.LockException as exception: # Try till the timeout has passed timeoutend = current_time() + timeout while timeoutend > current_time(): # Wait a bit time.sleep(check_interval) # Try again try: # We already tried to the get the lock # If fail_when_locked is true, then stop trying if fail_when_locked: raise exceptions.AlreadyLocked(exception) else: # pragma: no cover # We've got the lock fh = self._get_lock(fh) break except exceptions.LockException: pass else: # We got a timeout... reraising raise exceptions.LockException(exception) # Prepare the filehandle (truncate if needed) fh = self._prepare_fh(fh) self.fh = fh return fh
[docs] def release(self): '''Releases the currently locked file handle''' if self.fh: self.fh.close() self.fh = None
def _get_fh(self): '''Get a new filehandle''' return open(self.filename, self.mode) def _get_lock(self, fh): ''' Try to lock the given filehandle returns LockException if it fails''' portalocker.lock(fh, self.flags) return fh def _prepare_fh(self, fh): ''' Prepare the filehandle for usage If truncate is a number, the file will be truncated to that amount of bytes ''' if self.truncate: fh.seek(0) fh.truncate(0) return fh def __enter__(self): return self.acquire() def __exit__(self, type_, value, tb): self.release() def __delete__(self, instance): # pragma: no cover instance.release()
class RLock(Lock): """ A reentrant lock, functions in a similar way to threading.RLock in that it can be acquired multiple times. When the corresponding number of release() calls are made the lock will finally release the underlying file lock. """ def __init__( self, filename, mode='a', timeout=DEFAULT_TIMEOUT, check_interval=DEFAULT_CHECK_INTERVAL, fail_when_locked=False, flags=LOCK_METHOD): super(RLock, self).__init__(filename, mode, timeout, check_interval, fail_when_locked, flags) self._acquire_count = 0 def acquire( self, timeout=None, check_interval=None, fail_when_locked=None): if self._acquire_count >= 1: fh = self.fh else: fh = super(RLock, self).acquire(timeout, check_interval, fail_when_locked) self._acquire_count += 1 return fh def release(self): if self._acquire_count == 0: raise exceptions.LockException( "Cannot release more times than acquired") if self._acquire_count == 1: super(RLock, self).release() self._acquire_count -= 1 class TemporaryFileLock(Lock): def __init__(self, filename='.lock', timeout=DEFAULT_TIMEOUT, check_interval=DEFAULT_CHECK_INTERVAL, fail_when_locked=True, flags=LOCK_METHOD): Lock.__init__(self, filename=filename, mode='w', timeout=timeout, check_interval=check_interval, fail_when_locked=fail_when_locked, flags=flags) atexit.register(self.release) def release(self): Lock.release(self) if os.path.isfile(self.filename): # pragma: no branch os.unlink(self.filename)