From f98d671ac11252d7920dbbfb406a8ad30a4c4f42 Mon Sep 17 00:00:00 2001
From: Mathieu Sornay <mathieu.sornay@ercom.fr>
Date: Wed, 16 Nov 2016 12:49:24 +0100
Subject: [PATCH 1/2] Cancelled lock waiter wakes up the next one if any

---
 asyncio/locks.py     | 17 ++++++++++++-----
 tests/test_pep492.py | 25 +++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 5 deletions(-)

diff --git a/asyncio/locks.py b/asyncio/locks.py
index deefc938..92661830 100644
--- a/asyncio/locks.py
+++ b/asyncio/locks.py
@@ -176,6 +176,10 @@ def acquire(self):
             yield from fut
             self._locked = True
             return True
+        except futures.CancelledError:
+            if not self._locked:
+                self._wake_up_first()
+            raise
         finally:
             self._waiters.remove(fut)
 
@@ -192,14 +196,17 @@ def release(self):
         """
         if self._locked:
             self._locked = False
-            # Wake up the first waiter who isn't cancelled.
-            for fut in self._waiters:
-                if not fut.done():
-                    fut.set_result(True)
-                    break
+            self._wake_up_first()
         else:
             raise RuntimeError('Lock is not acquired.')
 
+    def _wake_up_first(self):
+        """Wake up the first waiter who isn't cancelled."""
+        for fut in self._waiters:
+            if not fut.done():
+                fut.set_result(True)
+                break
+
 
 class Event:
     """Asynchronous equivalent to threading.Event.
diff --git a/tests/test_pep492.py b/tests/test_pep492.py
index d5b85224..3882d835 100644
--- a/tests/test_pep492.py
+++ b/tests/test_pep492.py
@@ -71,6 +71,31 @@ async def test(lock):
             self.loop.run_until_complete(test(primitive))
             self.assertFalse(primitive.locked())
 
+    def test_finished_waiter_cancelled(self):
+
+        async def create_waiter(lock, fut):
+            fut.set_result(True)
+            async with lock:
+                pass
+
+        async def runner():
+            lock = asyncio.Lock(loop=self.loop)
+
+            await lock.acquire()
+
+            fut = self.loop.create_future()
+            task = asyncio.ensure_future(create_waiter(lock, fut),
+                                             loop=self.loop)
+            await fut
+
+            lock.release()
+            task.cancel()
+
+            async with lock:
+                pass
+
+        self.loop.run_until_complete(runner())
+
 
 class StreamReaderTests(BaseTest):
 

From 3bc7f442512a4191780b530c8de3e8938ba91972 Mon Sep 17 00:00:00 2001
From: msornay <msornay@gmail.com>
Date: Fri, 18 Nov 2016 00:41:59 +0100
Subject: [PATCH 2/2] Lock waiter cancel race test

Python issue #27585
---
 tests/test_locks.py  | 23 +++++++++++++++++++++++
 tests/test_pep492.py | 25 -------------------------
 2 files changed, 23 insertions(+), 25 deletions(-)

diff --git a/tests/test_locks.py b/tests/test_locks.py
index 152948c8..fab97521 100644
--- a/tests/test_locks.py
+++ b/tests/test_locks.py
@@ -176,6 +176,29 @@ def lockit(name, blocker):
         self.assertTrue(tb.cancelled())
         self.assertTrue(tc.done())
 
+    def test_finished_waiter_cancelled(self):
+        lock = asyncio.Lock(loop=self.loop)
+
+        ta = asyncio.Task(lock.acquire(), loop=self.loop)
+        test_utils.run_briefly(self.loop)
+        self.assertTrue(lock.locked())
+
+        tb = asyncio.Task(lock.acquire(), loop=self.loop)
+        test_utils.run_briefly(self.loop)
+        self.assertEqual(len(lock._waiters), 1)
+
+        # Create a second waiter, wake up the first, and cancel it.
+        # Without the fix, the second was not woken up.
+        tc = asyncio.Task(lock.acquire(), loop=self.loop)
+        lock.release()
+        tb.cancel()
+        test_utils.run_briefly(self.loop)
+
+        self.assertTrue(lock.locked())
+        self.assertTrue(ta.done())
+        self.assertTrue(tb.cancelled())
+        self.assertTrue(tc.done())
+
     def test_release_not_acquired(self):
         lock = asyncio.Lock(loop=self.loop)
 
diff --git a/tests/test_pep492.py b/tests/test_pep492.py
index 3882d835..d5b85224 100644
--- a/tests/test_pep492.py
+++ b/tests/test_pep492.py
@@ -71,31 +71,6 @@ async def test(lock):
             self.loop.run_until_complete(test(primitive))
             self.assertFalse(primitive.locked())
 
-    def test_finished_waiter_cancelled(self):
-
-        async def create_waiter(lock, fut):
-            fut.set_result(True)
-            async with lock:
-                pass
-
-        async def runner():
-            lock = asyncio.Lock(loop=self.loop)
-
-            await lock.acquire()
-
-            fut = self.loop.create_future()
-            task = asyncio.ensure_future(create_waiter(lock, fut),
-                                             loop=self.loop)
-            await fut
-
-            lock.release()
-            task.cancel()
-
-            async with lock:
-                pass
-
-        self.loop.run_until_complete(runner())
-
 
 class StreamReaderTests(BaseTest):