locking - Python Conditional "With" Lock Design

Question

I am trying to do some shared locking using with statements

def someMethod(self, hasLock = False):
     with self.my_lock:
         self.somethingElse(hasLock=True)


def somethingElse(self, hasLock = False):
    #I want this to be conditional...
    with self.my_lock:
          print 'i hate hello worlds"

That make sense? I basically only want to do the with if I don't already have the lock.

On top of being able to accomplish this, is it a bad design? Should I just acquire/release myself?

Answer 1

Just use a threading.RLock which is re-entrant meaning it can be acquired multiple times by the same thread.

http://docs.python.org/library/threading.html#rlock-objects

For clarity, the RLock is used in the with statements, just like in your sample code:

lock = threading.RLock()

def func1():
    with lock:
        func2()

def func2():
    with lock: # this does not block even though the lock is acquired already
        print 'hello world'

As far as whether or not this is bad design, we'd need more context. Why both of the functions need to acquire the lock? When is func2 called by something other than func1?