asyncio: Change bounded semaphore into a subclass, like threading.[Bounded]Semaphore.

Lib/asyncio/locks.py

@@ -336,22 +336,15 @@ class Semaphore:
 
     Semaphores also support the context manager protocol.
 
-    The first optional argument gives the initial value for the internal
+    The optional argument gives the initial value for the internal
     counter; it defaults to 1. If the value given is less than 0,
     ValueError is raised.
-
-    The second optional argument determines if the semaphore can be released
-    more than initial internal counter value; it defaults to False. If the
-    value given is True and number of release() is more than number of
-    successful acquire() calls ValueError is raised.
     """
 
-    def __init__(self, value=1, bound=False, *, loop=None):
+    def __init__(self, value=1, *, loop=None):
         if value < 0:
             raise ValueError("Semaphore initial value must be >= 0")
         self._value = value
-        self._bound = bound
-        self._bound_value = value
         self._waiters = collections.deque()
         self._locked = (value == 0)
         if loop is not None:
@@ -402,17 +395,9 @@ class Semaphore:
         """Release a semaphore, incrementing the internal counter by one.
         When it was zero on entry and another coroutine is waiting for it to
         become larger than zero again, wake up that coroutine.
-
-        If Semaphore is created with "bound" parameter equals true, then
-        release() method checks to make sure its current value doesn't exceed
-        its initial value. If it does, ValueError is raised.
         """
-        if self._bound and self._value >= self._bound_value:
-            raise ValueError('Semaphore released too many times')
-
         self._value += 1
         self._locked = False
-
         for waiter in self._waiters:
             if not waiter.done():
                 waiter.set_result(True)
@@ -429,3 +414,20 @@ class Semaphore:
     def __iter__(self):
         yield from self.acquire()
         return self
+
+
+class BoundedSemaphore(Semaphore):
+    """A bounded semaphore implementation.
+
+    This raises ValueError in release() if it would increase the value
+    above the initial value.
+    """
+
+    def __init__(self, value=1, *, loop=None):
+        self._bound_value = value
+        super().__init__(value, loop=loop)
+
+    def release(self):
+        if self._value >= self._bound_value:
+            raise ValueError('BoundedSemaphore released too many times')
+        super().release()

Lib/test/test_asyncio/test_locks.py

@@ -805,7 +805,7 @@ class SemaphoreTests(unittest.TestCase):
         self.assertFalse(sem._waiters)
 
     def test_release_not_acquired(self):
-        sem = locks.Semaphore(bound=True, loop=self.loop)
+        sem = locks.BoundedSemaphore(loop=self.loop)
 
         self.assertRaises(ValueError, sem.release)