gistfile1.py

import gc
import threading
import time

lock = threading.Lock()
sig = threading.Event()

class C(object):
    def __del__(self):
        print "In __del__"
        with lock:
            print "Got lock in __del__!"

def thread_a():
    c = C()
    print "Created", c
    del c
    print "Deleted it"
    sig.wait()
    print "Starting GC"
    gc.collect()

def thread_b():
    with lock:
        print "Got lock in thread_b"
        sig.set()
        time.sleep(2)
        print "Releasing lock in thread_b"

if __name__ == "__main__":
    tha = threading.Thread(target=thread_a)
    thb = threading.Thread(target=thread_b)
    tha.start()
    thb.start()
    tha.join()
    thb.join()
    print "Bye!"

# Results:
# Created <__main__.C object at 0x00007fc6ccf95898>
# Deleted it
# Got lock in thread_b
# Starting GC
# In __del__
# Releasing lock in thread_b
# Got lock in __del__!
# Bye!