Reserves a message previously offered by this multitype_join messaging block.
virtual bool reserve( runtime_object_identity _MsgId, _Inout_ ITarget<_Destination_type> * _PTarget );
The runtime_object_identity of the message object being reserved.
A pointer to the target block that is calling the reserve method.
true if the message was successfully reserved, false otherwise. Reservations can fail for many reasons, including: the message was already reserved or accepted by another target, the source could deny reservations, and so forth.
After you call reserve, if it succeeds, you must call either consume or release in order to take or give up possession of the message, respectively.