dynamolock: improve cancelability of acquireLock

When acquireLock() begins sleeping before a retry, it previously would not
return until after the full sleep interval had elapsed, which would cause the
caller to block for up to the configurable refresh period even after
cancellation.  This change allows immediate return should the context be
cancelled while sleeping.

Addresses #106

CONTRIBUTORS

@@ -5,4 +5,5 @@ Pawan Bishnoi [email protected]
 Alexandre Picard-Lemieux [email protected]
 Charlie Vieth ([email protected])
 Daniel Gil ([email protected])
-David Becher ([email protected])
+David Becher ([email protected])
+Jason Tackaberry ([email protected]))

client.go

@@ -317,17 +317,18 @@ func (c *Client) acquireLock(ctx context.Context, opt *acquireLockOptions) (*Loc
 	}
 
 	for {
-		if err := ctx.Err(); err != nil {
-			return nil, err
-		}
 		l, err := c.storeLock(ctx, &getLockOptions)
 		if err != nil {
 			return nil, err
 		} else if l != nil {
 			return l, nil
 		}
 		c.logger.Println("Sleeping for a refresh period of ", getLockOptions.refreshPeriodDuration)
-		time.Sleep(getLockOptions.refreshPeriodDuration)
+		select {
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		case <-time.After(getLockOptions.refreshPeriodDuration):
+		}
 	}
 }