Model-driven software development often involves several related models. When models are updated, the updates need to be propagated across all models to make them consistent. A bidirectional model transformation keeps two models consistent by updating one model in accordance with the other. However, it does not work when the two models are modified at the same time.
In this paper we propose a new algorithm that wraps any bidirectional transformation into a synchronizer with the help of a model difference approach. The synchronizer enables parallel updates by taking the two original models, the two updated models as input and producing two new models where the updates are synchronized. We also examine the requirements for synchronizing parallel updates, and demonstrate that our algorithm satisfies the requirements if the bidirectional transformation satisfies the correctness property and the hippocraticness property. Implementation of our algorithm showed that it works well in a runtime management framework in practical cases.