Parallels C API Reference Guide
Increases the specified handle reference count by one.
Handles used within the Parallels API are thread safe. They can be used in multiple threads at the same time. To maintain the proper reference counting, the count should be increased each time a handle is passed to another thread by calling the PrlHandle_AddRef function. If this is not done, freeing a handle in one thread may destroy it while other threads are still using it.