Lock objects now support specifying token values and ownership checking

Lock.acquire() can now be provided a token. If provided, this value will be
used as the value stored in Redis to hold the lock.

Lock.owned() returns a boolean indicating whether the lock is owned by the
current instance.

Author: andymccurdy

CHANGES

@@ -1,4 +1,10 @@
 * 3.1.0 (in development)
+    * Added an owned method to Lock objects. owned returns a boolean
+      indicating whether the current lock instance still owns the lock.
+      Thanks Dave Johansen. #1112
+    * Allow lock.acquire() to accept an optional token argument. If
+      provided, the token argument is used as the unique value used to claim
+      the lock. Thankd Dave Johansen. #1112
     * Added a reacquire method to Lock objects. reaquire attempts to renew
       the lock such that the timeout is extended to the same value that the
       lock was initially acquired with. Thanks Ihor Kalnytskyi. #1014

redis/lock.py

@@ -149,7 +149,7 @@ def __enter__(self):
     def __exit__(self, exc_type, exc_value, traceback):
         self.release()
 
-    def acquire(self, blocking=None, blocking_timeout=None):
+    def acquire(self, blocking=None, blocking_timeout=None, token=None):
         """
         Use Redis to hold a shared, distributed lock named ``name``.
         Returns True once the lock is acquired.
@@ -159,9 +159,18 @@ def acquire(self, blocking=None, blocking_timeout=None):
 
         ``blocking_timeout`` specifies the maximum number of seconds to
         wait trying to acquire the lock.
+
+        ``token`` specifies the token value to be used. If provided, token
+        must be a bytes object or a string that can be encoded to a bytes
+        object with the default encoding. If a token isn't specified, a UUID
+        will be generated.
         """
         sleep = self.sleep
-        token = uuid.uuid1().hex.encode()
+        if token is None:
+            token = uuid.uuid1().hex.encode()
+        else:
+            encoder = self.redis.connection_pool.get_encoder()
+            token = encoder.encode(token)
         if blocking is None:
             blocking = self.blocking
         if blocking_timeout is None:
@@ -195,6 +204,19 @@ def locked(self):
         """
         return self.redis.get(self.name) is not None
 
+    def owned(self):
+        """
+        Returns True if this key is locked by this lock, otherwise False.
+        """
+        stored_token = self.redis.get(self.name)
+        # need to always compare bytes to bytes
+        # TODO: this can be simplified when the context manager is finished
+        if stored_token and not isinstance(stored_token, bytes):
+            encoder = self.redis.connection_pool.get_encoder()
+            stored_token = encoder.encode(stored_token)
+        return self.local.token is not None and \
+            stored_token == self.local.token
+
     def release(self):
         "Releases the already acquired lock"
         expected_token = self.local.token

tests/test_lock.py

@@ -2,10 +2,16 @@
 import time
 
 from redis.exceptions import LockError, LockNotOwnedError
+from redis.client import Redis
 from redis.lock import Lock
+from .conftest import _get_client
 
 
 class TestLock(object):
+    @pytest.fixture()
+    def r_decoded(self, request):
+        return _get_client(Redis, request=request, decode_responses=True)
+
     def get_lock(self, redis, *args, **kwargs):
         kwargs['lock_class'] = Lock
         return redis.lock(*args, **kwargs)
@@ -18,6 +24,16 @@ def test_lock(self, r):
         lock.release()
         assert r.get('foo') is None
 
+    def test_lock_token(self, r):
+        lock = self.get_lock(r, 'foo')
+        assert lock.acquire(blocking=False, token='test')
+        assert r.get('foo') == b'test'
+        assert lock.local.token == b'test'
+        assert r.ttl('foo') == -1
+        lock.release()
+        assert r.get('foo') is None
+        assert lock.local.token is None
+
     def test_locked(self, r):
         lock = self.get_lock(r, 'foo')
         assert lock.locked() is False
@@ -26,6 +42,30 @@ def test_locked(self, r):
         lock.release()
         assert lock.locked() is False
 
+    def _test_owned(self, client):
+        lock = self.get_lock(client, 'foo')
+        assert lock.owned() is False
+        lock.acquire(blocking=False)
+        assert lock.owned() is True
+        lock.release()
+        assert lock.owned() is False
+
+        lock2 = self.get_lock(client, 'foo')
+        assert lock.owned() is False
+        assert lock2.owned() is False
+        lock2.acquire(blocking=False)
+        assert lock.owned() is False
+        assert lock2.owned() is True
+        lock2.release()
+        assert lock.owned() is False
+        assert lock2.owned() is False
+
+    def test_owned(self, r):
+        self._test_owned(r)
+
+    def test_owned_with_decoded_responses(self, r_decoded):
+        self._test_owned(r_decoded)
+
     def test_competing_locks(self, r):
         lock1 = self.get_lock(r, 'foo')
         lock2 = self.get_lock(r, 'foo')