CORBA 2.6.1 Programmer's Guide for C++

The client role adds the connect feature to the transfer role. The client event-handler user asks the client event handler to connect to a specific
address. Depending on the outcome of the connect operation, the client event handler performs either a
connected or a connect_failed upcall
to the client event-handler user.
The basic functions of a client event-handler user and a client event handler are shown in Figure 12–5.
Figure 12.5. Client Event Handler and Event-Handler User
Server Event Handler and Event-Handler User
No additional features, beyond those provided by the transfer event handler and transfer event-handler user, are required to perform the server
roles. Therefore, there are no base server event-handler and event-handler user components; all definitions are inherited from the transfer
classes.
Header Files
Header files containing definitions for the event framework APIs are located in the $NSD_ROOT/include/nsdevent subdirectory, and include the
following:
ehbase.h
Contains abstract classes defining roles for client-server connections and data transfer.
message.h
Contains classes and methods to assemble and disassemble messages.
gfsehoss.h
Contains classes and methods for Guardian file-system I/O.
gcfehoss.h
Builds on the definitions in gfsehoss.h and adds classes and methods for TS/MP I/O.
sockeh.h
Contains classes and methods for TCP/IP socket I/O.
The
$NSD_ROOT/include/nsdevent subdirectory also contains the vthread.h and timer.h header files, whose contents are described in Writing
Multithreaded Applications, and several other header files containing definitions for NonStop CORBA internal use.
Caution:
The classes described in the following sections contain some public methods that are required for internal use
by NonStop CORBA but are not recommended for application use. Applications should use only those methods
that are described in the NonStop CORBA 2.6.1 Programmer's Reference.
Base Event-Handler Interfaces
The event-handler interfaces are defined in the header file ehbase.h and consist of the following abstract classes:
Fw_Transfer_EH_User
Fw_Transfer_EH
Fw_Client_EH_User
Fw_Client_EH
Fw_Server_EH_User
Fw_Server_EH
Fw_Listener_EH_User
Fw_Listener_EH
The transfer classes, Fw_Transfer_EH_User and Fw_Transfer_EH, are base classes for the corresponding client and server classes. Each of the
other six classes represents a role that a client or server wrapper can play.
The event-handler interfaces operate on message objects and message data-descriptor objects, which are described in Event Framework
Messages and Message Data Descriptors.
For each method that your client or server wrapper uses from these abstract classes, your wrapper must either: