Why can I acquire the same lock twice?

[fostiropoulos]

It is not clear why I can acquire the same lock more than once e.g.

from filelock import Timeout, FileLock

file_path = "high_ground.txt"
lock_path = "high_ground.txt.lock"

lock = FileLock(lock_path, timeout=1)
lock.acquire()
lock.acquire()

Shouldn't this throw an error?

[fostiropoulos]

I did provide a fix in https://github.com/fostiropoulos/py-filelock but based on the other tests it seems like this is a supported use-case but it is unclear from the documentation how to correctly "lock" a file or what is the correct use-case of this library.

[asqui]

The reason that you can acquire the lock multiple times (within the same thread) like this is because FileLocks are reentrant, meaning that if you already hold the lock in a given thread, you can acquire it a second time in the same thread.

If you execute this code snippet in a second thread, or process (e.g. just run a second instance of your code snippet in a separate python interpreter) you'll see that the lock.acquire() will block.

See the last example at https://py-filelock.readthedocs.io/en/latest/#tutorial which illustrates this behaviour, and the Python standard library documentation for RLock for an explanation of reentrant locks: https://docs.python.org/3/library/threading.html#rlock-objects