locklib

Deadlocks are the most terrible enemies of all programmers who make multithreaded programs. If you are a one of them - this library is going to help you out.

How can I use it?

Get the locklib from the pip:

$ pip install locklib

And use a lock from this library as a usual Lock from the standard library:

from threading import Thread
from locklib import SmartLock


lock = SmartLock()
counter = 0

def function():
  global counter

  for _ in range(1000):
      with lock:
          counter += 1

thread_1 = Thread(target=function)
thread_2 = Thread(target=function)
thread_1.start()
thread_2.start()

assert counter == 2000

In this case the lock helps us not to get a race condition, as the standard Lock does. But! Let's trigger a deadlock and look what happens:

from threading import Thread
from locklib import SmartLock


lock_1 = SmartLock()
lock_2 = SmartLock()

def function_1():
  while True:
    with lock_1:
      with lock_2:
        pass

def function_2():
  while True:
    with lock_2:
      with lock_1:
        pass

thread_1 = Thread(target=function_1)
thread_2 = Thread(target=function_2)
thread_1.start()
thread_2.start()

And... We have an exception like this:

...
locklib.errors.DeadLockError: A cycle between 1970256th and 1970257th threads has been detected.

Deadlocks are impossible for this lock!

If you want to catch the exception, import this from the locklib too:

from locklib import DeadLockError

How does it work?

Deadlock detection based on Wait-for Graph.