How to synchronize a Scene Graph?

Hello, when I have multiple Threads, reading and writing to a scene graph, how do I synchronize data over several nodes? I.e. when a character with a gun moves, the gun moves with him. A thread dedicated to calculating matrices of both objects might update the character first but before it is able to recalculate the gun's matrix the render thread is already drawing both. Inevitably this causes the character and the gun to be out of sync... Now this doesn't only apply to the renderer but for the other threads, too.