3.3.5.2.3 Constructing a Logical Surface Compositor Reference Order
The Desktop Window Manager triggers the Compositor Reference event when a logical surface has been referenced by the compositor on the server.
The compose desktop mediator constructs the TS_COMPDESK_LSURFACE_COMPREF_PENDING message using the unique hLSurf value, to instruct the client to retain the logical surface until the compositor retrieves the logical surface.