RfD: Automagically making a class instance 'synchronized' (draft impl.)

Gerhard Häring gh_pythonlist at gmx.de
Tue Jun 11 22:54:23 CEST 2002


For one of my projects, I'll need something not quite unlike the
following code. It's not tested, yet, but it looks ok and complete to
me. I thought that it could be useful to other developers who need to
use multithreading, so I'm posting it here. Maybe something like this
would even be a useful addition to the Standard Library?

Gerhard


from threading import RLock

class Connection:
    def begin(self):
        print "begin"

    def commit(self):
        print "commit"

class LockingWrapper:
    def __init__(self, proxy, obj):
        self.proxy = proxy
        self.obj = obj

    def __call__(self, *args, **kwargs):
        self.proxy.__dict__["rlock"].acquire(1)
        try:
            self.obj(*args, **kwargs)
        except:
            self.proxy.__dict__["rlock"].release()
            raise
            return
        self.proxy.__dict__["rlock"].release()

class LockingProxy:
    """LockingProxy proxies an instance of a class, so that in that instance,
    only one method can be active at any given point in time. In Java-speak, it
    automatically makes all methods of this class 'synchronized'."""
    def __init__(self, obj, methodnames):
        """obj -> a callable
           methodnames -> a list of method names"""
        self.__dict__["obj"] = obj
        self.__dict__["rlock"] = RLock()
        self.__dict__["methodnames"] = methodnames

    def __getattr__(self, attr):
        val = getattr(self.__dict__["obj"], attr)
        if attr not in self.__dict__["methodnames"]:
            return val
        else:
            return LockingWrapper(self, val)

conn = Connection()
lp = LockingProxy(conn, ["begin", "commit"])
lp.begin()
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