Issue #850728: Add a *timeout* parameter to the `acquire()` method of

`threading.Semaphore` objects.  Original patch by Torsten Landschoff.

Doc/library/threading.rst

@@ -596,7 +596,7 @@ waiting until some other thread calls :meth:`release`.
    defaults to ``1``. If the *value* given is less than 0, :exc:`ValueError` is
    raised.
 
-   .. method:: acquire(blocking=True)
+   .. method:: acquire(blocking=True, timeout=None)
 
       Acquire a semaphore.
 
@@ -607,14 +607,18 @@ waiting until some other thread calls :meth:`release`.
       interlocking so that if multiple :meth:`acquire` calls are blocked,
       :meth:`release` will wake exactly one of them up.  The implementation may
       pick one at random, so the order in which blocked threads are awakened
-      should not be relied on.  There is no return value in this case.
-
-      When invoked with *blocking* set to true, do the same thing as when called
-      without arguments, and return true.
+      should not be relied on.  Returns true (or blocks indefinitely).
 
       When invoked with *blocking* set to false, do not block.  If a call
-      without an argument would block, return false immediately; otherwise, do
-      the same thing as when called without arguments, and return true.
+      without an argument would block, return false immediately; otherwise,
+      do the same thing as when called without arguments, and return true.
+
+      When invoked with a *timeout* other than None, it will block for at
+      most *timeout* seconds.  If acquire does not complete successfully in
+      that interval, return false.  Return true otherwise.
+
+      .. versionchanged:: 3.2
+         The *timeout* parameter is new.
 
    .. method:: release()
 

Lib/test/lock_tests.py

@@ -521,6 +521,19 @@ class BaseSemaphoreTests(BaseTestCase):
         # ordered.
         self.assertEqual(sorted(results), [False] * 7 + [True] *  3 )
 
+    def test_acquire_timeout(self):
+        sem = self.semtype(2)
+        self.assertRaises(ValueError, sem.acquire, False, timeout=1.0)
+        self.assertTrue(sem.acquire(timeout=0.005))
+        self.assertTrue(sem.acquire(timeout=0.005))
+        self.assertFalse(sem.acquire(timeout=0.005))
+        sem.release()
+        self.assertTrue(sem.acquire(timeout=0.005))
+        t = time.time()
+        self.assertFalse(sem.acquire(timeout=0.5))
+        dt = time.time() - t
+        self.assertTimeout(dt, 0.5)
+
     def test_default_value(self):
         # The default initial value is 1.
         sem = self.semtype()

Lib/threading.py

@@ -290,8 +290,11 @@ class _Semaphore(_Verbose):
         self._cond = Condition(Lock())
         self._value = value
 
-    def acquire(self, blocking=True):
+    def acquire(self, blocking=True, timeout=None):
+        if not blocking and timeout is not None:
+            raise ValueError("can't specify timeout for non-blocking acquire")
         rc = False
+        endtime = None
         self._cond.acquire()
         while self._value == 0:
             if not blocking:
@@ -299,7 +302,14 @@ class _Semaphore(_Verbose):
             if __debug__:
                 self._note("%s.acquire(%s): blocked waiting, value=%s",
                            self, blocking, self._value)
-            self._cond.wait()
+            if timeout is not None:
+                if endtime is None:
+                    endtime = _time() + timeout
+                else:
+                    timeout = endtime - _time()
+                    if timeout <= 0:
+                        break
+            self._cond.wait(timeout)
         else:
             self._value = self._value - 1
             if __debug__:

Misc/ACKS

@@ -431,6 +431,7 @@ Ivan Krstić
 Andrew Kuchling
 Vladimir Kushnir
 Cameron Laird
+Torsten Landschoff
 Tino Lange
 Andrew Langmead
 Detlef Lannert

Misc/NEWS

@@ -315,6 +315,9 @@ C-API
 Library
 -------
 
+- Issue #850728: Add a *timeout* parameter to the `acquire()` method of
+  `threading.Semaphore` objects.  Patch by Torsten Landschoff.
+
 - Issue #8322: Add a *ciphers* argument to SSL sockets, so as to change the
   available cipher list.  Helps fix test_ssl with OpenSSL 1.0.0.