Add feature region.key_is_locked()

Added new region method :meth:`.Region.key_is_locked`. Returns True if the
given key is subject to the dogpile lock, which would indicate that the
generator function is running at that time. Pull request courtesy Bastien
Gerard.

Fixes: #101
Closes: #198
Pull-request: https://github.com/sqlalchemy/dogpile.cache/pull/198
Pull-request-sha: 8a5ec7aa07dbdfc654617632ffffae6834078263

Change-Id: I8449beeeef0052ac11a4e3d2e8305e10ba70a765

2 files changed, 28 insertions, 0 deletions

diff --git a/tests/cache/_fixtures.py b/tests/cache/_fixtures.py
index 1be5a2c..539e27d 100644
--- a/tests/cache/_fixtures.py
+++ b/tests/cache/_fixtures.py
@@ -6,6 +6,7 @@ from threading import Lock
 from threading import Thread
 import time
 from unittest import TestCase
+import uuid
 
 import pytest
 
@@ -109,6 +110,21 @@ class _GenericBackendTest(_GenericBackendFixture, TestCase):
         backend.delete("some_key")
         eq_(backend.get_serialized("some_key"), NO_VALUE)
 
+    def test_region_is_key_locked(self):
+        reg = self._region()
+        random_key = str(uuid.uuid1())
+        assert not reg.get(random_key)
+        eq_(reg.key_is_locked(random_key), False)
+        # ensures that calling key_is_locked doesn't acquire the lock
+        eq_(reg.key_is_locked(random_key), False)
+
+        mutex = reg.backend.get_mutex(random_key)
+        if mutex:
+            mutex.acquire()
+            eq_(reg.key_is_locked(random_key), True)
+            mutex.release()
+            eq_(reg.key_is_locked(random_key), False)
+
     def test_region_set_get_value(self):
         reg = self._region()
         reg.set("some key", "some value")
@@ -387,11 +403,15 @@ class _GenericMutexTest(_GenericBackendFixture, TestCase):
         backend = self._backend()
         mutex = backend.get_mutex("foo")
 
+        assert not mutex.locked()
         ac = mutex.acquire()
         assert ac
         ac2 = mutex.acquire(False)
+        assert mutex.locked()
         assert not ac2
         mutex.release()
+        assert not mutex.locked()
+
         ac3 = mutex.acquire()
         assert ac3
         mutex.release()
@@ -470,6 +490,9 @@ class MockMutex(object):
     def release(self):
         return
 
+    def locked(self):
+        return False
+
 
 class MockBackend(CacheBackend):
     def __init__(self, arguments):
diff --git a/tests/cache/test_region.py b/tests/cache/test_region.py
index 467e16a..0a10beb 100644
--- a/tests/cache/test_region.py
+++ b/tests/cache/test_region.py
@@ -202,6 +202,11 @@ class RegionTest(TestCase):
 
         eq_(reg.get_or_create("some key", creator), "some value")
 
+    def test_key_is_locked(self):
+        reg = self._region()
+
+        eq_(reg.key_is_locked("some key"), False)
+
     def test_multi_creator(self):
         reg = self._region()