--- old/threading.py	2006-12-01 22:14:19.000000000 +0000
+++ new/threading.py	2006-12-01 22:12:26.000000000 +0000
@@ -209,13 +209,26 @@
                 # we'll be unresponsive.  The scheme here sleeps very
                 # little at first, longer as time goes on, but never longer
                 # than 20 times per second (or the timeout time remaining).
-                endtime = _time() + timeout
+                time = _time()
+                endtime = time + timeout
                 delay = 0.0005 # 500 us -> initial delay of 1 ms
                 while True:
                     gotit = waiter.acquire(0)
                     if gotit:
                         break
-                    remaining = endtime - _time()
+                    lasttime = time
+                    time = _time()
+                    delta = time - lasttime
+                    # If the current time is smaller than the last polled time,
+                    # the system clock was set back and must be adjusted for.
+                    # If the delta was sufficiently large (greater than 10
+                    # seconds), then the system clock was probably set forward
+                    # and should be adjusted for.  The 10 second window could
+                    # optionally be made a tunable parameter for applications
+                    # where 10 seconds is unreasonable.
+                    if delta < 0.0 or delta > 10.0:
+                        endtime += delta - delay
+                    remaining = endtime - time
                     if remaining <= 0:
                         break
                     delay = min(delay * 2, remaining, .05)