Interface for ensuring a roundtrip to the client implementation.
This interface is identical to
ei_callback but is intended for
the EIS implementation to enforce a roundtrip to the client.
Note that for a client to receive objects of this type, it must announce
support for this interface in
Since Version1 Request Opcode0
||request-specific data for the callback|
Immediately after sending this request, the object is considered destroyed by the EIS implementation. It must no longer be used by the client.
Notify the EIS implementation when the related event is done. Immediately after this request
ei_pingpong object is destroyed by the client and as such must not be used