Add AtomicCounter class to threading module

Lib/test/test_threading.py

@@ -2339,6 +2339,30 @@ def run_last():
         self.assertIn("RuntimeError: can't register atexit after shutdown",
                 err.decode())
 
+class TestAtomicCounter(unittest.TestCase):
+    def setUp(self):
+        self.counter = threading.AtomicCounter()
+
+    def test_initial_value(self):
+        self.assertEqual(self.counter.get(), 0)
+
+    def test_increment(self):
+        self.counter.inc()
+        self.assertEqual(self.counter.get(), 1)
+        self.counter.inc(5)
+        self.assertEqual(self.counter.get(), 6)
+
+    def test_decrement(self):
+        self.counter.dec()
+        self.assertEqual(self.counter.get(), -1)
+        self.counter.dec(5)
+        self.assertEqual(self.counter.get(), -6)
+
+    def test_increment_and_decrement(self):
+        self.counter.inc(10)
+        self.counter.dec(3)
+        self.assertEqual(self.counter.get(), 7)
+
 
 if __name__ == "__main__":
     unittest.main()

Lib/threading.py

@@ -29,7 +29,7 @@
            'Barrier', 'BrokenBarrierError', 'Timer', 'ThreadError',
            'setprofile', 'settrace', 'local', 'stack_size',
            'excepthook', 'ExceptHookArgs', 'gettrace', 'getprofile',
-           'setprofile_all_threads','settrace_all_threads']
+           'setprofile_all_threads','settrace_all_threads', 'AtomicCounter']
 
 # Rename some stuff so "from threading import *" is safe
 _start_joinable_thread = _thread.start_joinable_thread
@@ -857,6 +857,31 @@ def _newname(name_template):
 _dangling = WeakSet()
 
 
+class AtomicCounter:
+    """Threadsafe counter.
+
+    Returns the value after inc/dec operations.
+    """
+
+    def __init__(self, initial=0):
+        self._value = initial
+        self._lock = Lock()
+
+    def inc(self, n=1):
+        with self._lock:
+            self._value += n
+            return self._value
+
+    def dec(self, n=1):
+        with self._lock:
+            self._value -= n
+            return self._value
+
+    def get(self):
+        with self._lock:
+            return self._value
+
+
 # Main class for threads
 
 class Thread: