Python Conditional "With" Lock Design
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
?
The Python or
is short circuiting so you can make the locking conditional:
def somethingElse(self, hasLock = False): #I want this to be conditional... with hasLock or self.my_lock: print 'i hate hello worlds'
Unfortunately it's not quite that easy, because a boolean isn't a valid return from a with
statement. You'll need to create a class with the __enter__
and __exit__
to wrap the boolean True
value.
Here's one possible implementation that I haven't tested.
from contextlib import contextmanager@contextmanagerdef withTrue(): yield Truedef withbool(condition): if condition: return withTrue() return Falsedef somethingElse(self, hasLock = False): with withbool(hasLock) or self.my_lock(): print 'i hate hello worlds'
This is a lot of boilerplate for something so simple, so the RLock solution looks like a winner. This solution might be useful in a different context though.
Using with statement is better than just acquire()
and release()
functions. This way, if an error occurs, the locks will be released.