jztools.filelock#

Fcntl / flock Unix advisory file locking with support for exclusive and shared locks.

Classes

CompoundFileLock(file_lock, *locks)

Behaves like a FileLock object but acquires/releases one or more locks (assumed to have the threading.Lock interface) simultaneously.

FileLock(filename[, mode, poll_interval])

Fcntl/flock file locking.

Mode(val)

class jztools.filelock.FileLock(filename, mode='exclusive', poll_interval=0.02)#

Bases: object

Fcntl/flock file locking. Shared locks can be re-acquired from any FileLock object or process. Exclusive locks can only be re-acquired from the same FileLock object and process. Note in particular that this object does not enforce exclusive locks between threads for the same lock object (use CompoundFileLock for this purpose).

If a file is moved while a lock is active, that lock will continue to be valid on the moved file. If it is deleted, however, that lock will continue to behave like the file existed, but it will not lock against a newly created file of the same name.

Lock acquisition for exclusive locks can implicitly upgrade or downgrade the lock:

Mode ‘exclusive’ can operate in ‘shared’ and ‘exclusive’ mode, with ‘exclusive’ being sticky: None -> acquire(mode=’shared’) -> ‘shared’; acquire(mode=’exclusive’) -> ‘exclusive’; acquire(mode=’shared’) -> ‘exclusive’; release() -> ‘exclusive’; release() -> ‘shared’; release() -> None

Mode ‘shared’ will result in an error if ‘exclusive’ is requested.: acquire(mode=’shared’) -> ‘shared’, acquire(mode=’exclusive’) -> Exception

Parameters:

  • filename – Name of file to apply advisory lock to.

  • mode – The maximum supported mode - one of 'shared' (or its alias 'read'), or 'exclusive' (or its alias 'write').

downgrade_max_mode()#

Ensures that the max mode is shared mode.

with_acquire(**acquire_kwargs)#

Context manager that fails if the lock type is not of the specified type, or if the acquire call times out.

acquire(timeout=-1, create=False, mode=None)#
Parameters:

create – Will create the lock file if mode is ‘write’/’exclusive’.

class jztools.filelock.CompoundFileLock(file_lock, *locks)#

Bases: FileLock

Behaves like a FileLock object but acquires/releases one or more locks (assumed to have the threading.Lock interface) simultaneously.

Parameters:

  • filename – Name of file to apply advisory lock to.

  • mode – The maximum supported mode - one of 'shared' (or its alias 'read'), or 'exclusive' (or its alias 'write').

acquire(timeout=-1, **kwargs)#
Parameters:

create – Will create the lock file if mode is ‘write’/’exclusive’.

with_acquire(timeout=-1, **kwargs)#

Context manager that fails if the lock type is not of the specified type, or if the acquire call times out.