implemented simple gc of released loc entries in mongo collection

lock.go

@@ -684,6 +684,22 @@ func (c *Client) sUnlock(ctx context.Context, resourceName, lockId string) error
 	return nil
 }
 
+// Gc removes all lock entries in the collection that have expired
+// Specifically this removes lock entries where exclusive.lockId is nil AND shared.count is 0
+func (c *Client) Gc(ctx context.Context) error {
+	// Get all empty locks and remove
+	selector := bson.M{
+		"exclusive.lockId": nil,
+		"shared.count":     0,
+	}
+
+	_, err := c.collection.DeleteMany(ctx, selector)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
 // lockFromDetails creates a lock struct from a lockId and a LockDetails struct.
 func lockFromDetails(lockId string, ld LockDetails) lock {
 	now := time.Now()

purge.go

@@ -45,6 +45,11 @@ func (p *purger) Purge(ctx context.Context) ([]LockStatus, error) {
 		}
 		allUnlocked = append(allUnlocked, unlocked...)
 	}
+	// Garbage collect unused lock records
+	err = p.client.Gc(ctx)
+	if err != nil {
+		return allUnlocked, err
+	}
 
 	return allUnlocked, nil
 }