example.py

#!/usr/bin/env python

import threading
import time

class Foo(object):

    def modify_bar(self, **kwargs):
        bar_id = kwargs['bar_id']

        print "working on bar id = %s" % bar_id

        time.sleep(3)

        print "done with bar id = %s" % bar_id

if __name__ == "__main__":
    class ModifyBarThread(threading.Thread):

        def __init__(self, foo, bar_id):
            self.foo = foo 
            self.bar_id = bar_id

            threading.Thread.__init__(self)

        def run(self):
            self.foo.modify_bar(bar_id=self.bar_id)


    foo = Foo()

    threads = []

    for i in range(3):
        thread = ModifyBarThread(foo, 1)
        threads.append(thread)
        thread.start()

    [thread.join() for thread in threads]

example2.py

import threading
import time

def synchronize(field_name):
    def inner_decorator(func):
        def wrapper(self, *args, **kwargs):
            object_id = kwargs[field_name]
           
            ready_to_start = False
           
            while not ready_to_start:
                with self._active_bars_lock:
                    if object_id not in self._active_bars:
                        self._active_bars.append(object_id)
                        ready_to_start = True
               
                if not ready_to_start:
                    time.sleep(1.0)
           
            try:
                ret = func(self, *args, **kwargs)
            finally:
                with self._active_bars_lock:
                    self._active_bars.remove(object_id)
           
            return ret
        return wrapper
    return inner_decorator

class Foo(object):

    def __init__(self):
        self._active_bars = []
        self._active_bars_lock = threading.Lock()
   
    @synchronize('bar_id')
    def modify_bar(self, **kwargs):
        bar_id = kwargs['bar_id']

        print "working on bar id = %s" % bar_id

        time.sleep(3)

        print "done with bar id = %s" % bar_id

if __name__ == "__main__":
    class ModifyBarThread(threading.Thread):

        def __init__(self, foo, bar_id):
            self.foo = foo
            self.bar_id = bar_id
           
            threading.Thread.__init__(self)

        def run(self):
            self.foo.modify_bar(bar_id=self.bar_id)

    foo = Foo()

    threads = []

    for i in range(3):
        thread = ModifyBarThread(foo, 1)
        threads.append(thread)
        thread.start()
   
    [thread.join() for thread in threads]

example3.py

if __name__ == "__main__":
    class ModifyBarThread(threading.Thread):

        def __init__(self, foo, bar_id):
            self.foo = foo 
            self.bar_id = bar_id

            threading.Thread.__init__(self)

        def run(self):
            self.foo.modify_bar(bar_id=self.bar_id)

    foo = Foo()

    threads = []

    for i in range(5):
        thread = ModifyBarThread(foo, 0 if i == 2 else 1)
        threads.append(thread)
        thread.start()

    [thread.join() for thread in threads]