non-blocking lock with 'with' statement

Question

As far as I know, the following code will be blocked if lock is already acquired by another thread.

It seems that non-blocking can be implemented by lock.acquire(0), but instead I have to use try-finally block instead with block.

lock = threading.Lock()

def func():
 with lock:
  # do something...

Is there any method to implement non-blocking lock acquisition?

Answer 1

@contextmanager
def nonblocking(lock):
    locked = lock.acquire(False)
    try:
        yield locked
    finally:
        if locked:
            lock.release()

lock = threading.Lock()
with nonblocking(lock) as locked:
    if locked:
        do_stuff()

Answer 2

Is there any method to implement non-blocking lock acquisition?

Yes. Just raise an exception if the lock can't be acquired immediately. Something like:

@contextlib.contextmanager
def non_blocking_lock(lock=threading.Lock()):
    if not lock.acquire(blocking=False):
        raise WouldBlockError
    try:
        yield lock
    finally:
        lock.release()

Usage:

with non_blocking_lock():
    # run with the lock acquired