From c4e94b90a84a1127078bdb9f63707eb71fedece3 Mon Sep 17 00:00:00 2001
From: Raymond Hettinger <python@rcn.com>
Date: Sat, 25 Mar 2006 12:15:04 +0000
Subject: [PATCH] Don't decrement below zero.  And add more tests.

---
 Lib/Queue.py           |  3 ++-
 Lib/test/test_queue.py | 20 +++++++++++++++++---
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/Lib/Queue.py b/Lib/Queue.py
index ad65cf0b579..51ad3542608 100644
--- a/Lib/Queue.py
+++ b/Lib/Queue.py
@@ -56,11 +56,12 @@ class Queue:
         """
         self.all_tasks_done.acquire()
         try:
-            self.unfinished_tasks = unfinished = self.unfinished_tasks - 1
+            unfinished = self.unfinished_tasks - 1
             if unfinished <= 0:
                 if unfinished < 0:
                     raise ValueError('task_done() called too many times')
                 self.all_tasks_done.notifyAll()
+            self.unfinished_tasks = unfinished
         finally:
             self.all_tasks_done.release()
 
diff --git a/Lib/test/test_queue.py b/Lib/test/test_queue.py
index 77a1c9da118..b3f24dff517 100644
--- a/Lib/test/test_queue.py
+++ b/Lib/test/test_queue.py
@@ -228,6 +228,9 @@ def worker(q):
     global cum
     while True:
         x = q.get()
+        if x is None:
+            q.task_done()
+            return
         cumlock.acquire()
         try:
             cum += x
@@ -239,18 +242,29 @@ def QueueJoinTest(q):
     global cum
     cum = 0
     for i in (0,1):
-        t = threading.Thread(target=worker, args=(q,))
-        t.setDaemon(True)
-        t.start()
+        threading.Thread(target=worker, args=(q,)).start()
     for i in xrange(100):
         q.put(i)
     q.join()
     verify(cum==sum(range(100)), "q.join() did not block until all tasks were done")
+    for i in (0,1):
+        q.put(None)         # instruct the threads to close
+    q.join()                # verify that you can join twice
+
+def QueueTaskDoneTest(q)
+    try:
+        q.task_done()
+    except ValueError:
+        pass
+    else:
+        raise TestFailed("Did not detect task count going negative")
 
 def test():
     q = Queue.Queue()
+    QueueTaskDoneTest(q)
     QueueJoinTest(q)
     QueueJoinTest(q)
+    QueueTaskDoneTest(q)
 
     q = Queue.Queue(QUEUE_SIZE)
     # Do it a couple of times on the same queue