Merge pull request ServiceStack#97 from mikkelfish/master

Fixed lock

src/ServiceStack.Redis/RedisLock.cs

@@ -16,7 +16,35 @@ public RedisLock(RedisClient redisClient, string key, TimeSpan? timeOut)
 			this.key = key;
 
 			ExecExtensions.RetryUntilTrue(
-				() => redisClient.SetEntryIfNotExists(key, "lock " + DateTime.UtcNow.ToUnixTime()),
+				() =>
+				    {
+                        //This pattern is taken from the redis command for SETNX http://redis.io/commands/setnx
+				        
+                        //Calculate a unix time for when the lock should expire
+                        TimeSpan realSpan = timeOut ?? new TimeSpan(365, 0, 0, 0); //if nothing is passed in the timeout hold for a year
+				        DateTime expireTime = DateTime.UtcNow.Add(realSpan);
+				        string lockString = (expireTime.ToUnixTime() + 1).ToString();
+                        
+                        //Try to set the lock, if it does not exist this will succeed and the lock is obtained
+				        var nx = redisClient.SetEntryIfNotExists(key, lockString);
+                        if (nx)
+                            return true;
+
+                        //If we've gotten here then a key for the lock is present. This could be because the lock is
+                        //correctly acquired or it could be because a client that had acquired the lock crashed (or didn't release it properly).
+                        //Therefore we need to get the value of the lock to see when it should expire
+				        string lockExpireString = redisClient.Get<string>(key);
+                        long lockExpireTime;
+                        if (!long.TryParse(lockExpireString, out lockExpireTime))
+                            return false;
+                        //If the expire time is greater than the current time then we can't let the lock go yet
+                        if (lockExpireTime > DateTime.UtcNow.ToUnixTime())
+                            return false;
+                        //If the expire time is less than the current time then it wasn't released properly and we can attempt to 
+                        //acquire the lock. This is done by setting the lock to our timeout string AND checking to make sure
+                        //that what is returned is the old timeout string in order to account for a possible race condition.
+                        return redisClient.GetAndSetEntry(key, lockString) == lockExpireString;
+				    },
 				timeOut
 			);
 		}

tests/ServiceStack.Redis.Tests/Examples/SimpleLocks.cs

@@ -97,6 +97,20 @@ public void Acquiring_lock_with_timeout()
 			}
 		}
 
+        [Test]
+        public void SimulateLockTimeout()
+        {
+            var redisClient = new RedisClient(TestConfig.SingleHost);
+            var waitFor = TimeSpan.FromMilliseconds(20);
+
+            var loc = redisClient.AcquireLock("testlock",waitFor);
+            Thread.Sleep(40); //should have lock expire
+            using(var newloc = redisClient.AcquireLock("testlock", waitFor))
+            {
+
+            }
+        }
+
 	}