Added a locking object with key expiry and LUA transactions

Author: Nati CT

redis/client.py

@@ -420,7 +420,12 @@ def lock(self, name, timeout=None, sleep=0.1):
         when the lock is in blocking mode and another client is currently
         holding the lock.
         """
-        return Lock(self, name, timeout=timeout, sleep=sleep)
+        from distutils.version import StrictVersion
+        version = self.info()['redis_version']
+        if StrictVersion(version) < StrictVersion('2.6.0'):
+            return Lock(self, name, timeout=timeout, sleep=sleep)
+        else:
+            return LuaLock(self, name, timeout=timeout, sleep=sleep)
 
     def pubsub(self, shard_hint=None):
         """
@@ -2211,3 +2216,94 @@ def release(self):
         self.acquired_until = None
         if delete_lock:
             self.redis.delete(self.name)
+
+
+class LuaLock(object):
+    """
+    Like Lock, but using key expiration and LUA for transactions.
+
+    Backward compatible with Lock,
+    except for not keeping released locks in redis.
+
+    NOTE: Requires Redis 2.6+
+    """
+    # KEYS[1] - lock name, ARGV[1] - timeout, ARGV[2] - timeout at
+    LUA_LOCK_ACQUIRE_SCRIPT = """
+        local ret = redis.call('setnx', KEYS[1], ARGV[2])
+        if (ret == 1) then
+            redis.call('expire', KEYS[1], ARGV[1])
+            return true
+        end
+        return false
+        """
+    LUA_LOCK_RELEASE_SCRIPT = """
+        if (redis.call('get', KEYS[1])) then
+            redis.call('del', KEYS[1])
+            return true
+        end
+        return false
+    """
+    LUA_LOCK_ACQUIRE = None
+    LUA_LOCK_RELEASE = None
+
+    def __init__(self, redis, name, timeout=None, sleep=0.1):
+        """
+        Create a new Lock instance named ``name`` using the Redis client
+        supplied by ``redis``.
+
+        ``timeout`` indicates a maximum life for the lock.
+        By default, it will remain locked until release() is called.
+
+        ``sleep`` indicates the amount of time to sleep per loop iteration
+        when the lock is in blocking mode and another client is currently
+        holding the lock.
+        """
+        self.redis = redis
+        self.name = name
+        self.acquired_until = None
+        self.timeout = timeout
+        self.sleep = sleep
+        if self.timeout and self.sleep > self.timeout:
+            raise LockError("'sleep' must be less than 'timeout'")
+        # If the Acquire/Release scripts are not in redis- load them
+        if not callable(LuaLock.LUA_LOCK_ACQUIRE):
+            LuaLock.LUA_LOCK_ACQUIRE = redis.register_script(
+                LuaLock.LUA_LOCK_ACQUIRE_SCRIPT)
+        if not callable(LuaLock.LUA_LOCK_RELEASE):
+            LuaLock.LUA_LOCK_RELEASE = redis.register_script(
+                LuaLock.LUA_LOCK_RELEASE_SCRIPT)
+
+    def __enter__(self):
+        return self.acquire()
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        self.release()
+
+    def acquire(self, blocking=True):
+        """
+        Use Redis to hold a shared, distributed lock named ``name``.
+        Returns True once the lock is acquired.
+
+        If ``blocking`` is False, always return immediately. If the lock
+        was acquired, return True, otherwise return False.
+        """
+        sleep = self.sleep
+        timeout = self.timeout if self.timeout else Lock.LOCK_FOREVER
+        while 1:
+            timeout_at = mod_time.time() + self.timeout if self.timeout \
+                else Lock.LOCK_FOREVER
+            if LuaLock.LUA_LOCK_ACQUIRE(keys=[self.name],
+                                        args=[int(timeout), timeout_at]):
+                self.acquired_until = timeout_at
+                return True
+            if not blocking:
+                return False
+            mod_time.sleep(sleep)
+
+    def release(self):
+        """
+        Releases the already acquired lock
+        """
+        if not LuaLock.LUA_LOCK_RELEASE(keys=[self.name]):
+            raise ValueError("Cannot release an unlocked lock")
+        self.acquired_until = None