Acquire the global scene graph write-lock.

The calling thread will block until the write-lock is available (no threads hold a global read-lock). The global write-lock is exclusive. Only a single thread can hold this lock and while it is held, no thread can acquire a global read-lock. While holding the global write-lock it is safe to modify the scene graph including adding/removing nodes, modifying field values, etc. Do not hold the global write-lock longer than necessary. See OIV.Inventor.SoDB.Writeunlock().

Note: Be sure the global write-lock is always released or there is a good chance the application will "dead lock" because all standard actions automatically attempt to acquire a global read-lock.

Reference