"Stack" example run-time scenario

The following scenario steps through the actions taken by the DSOM run time in response to each line of code in the second "Stack" client program presented above. The illustration following the scenario shows the processes, and the objects within them, that participate in these actions.

• Initialize an environment for error passing:

SOM _ InitEnvironment ( & e ) ;

• Initialize DSOM:

SOMD _ Init ( & e ) ;

This causes the creation of the DSOM Object Manager (with SOMDObjectMgr interface). The global variable SOMD_ObjectMgr points to this object.

• Initialize "Stack" class object:

StackNewClass ( Stack _ MajorVersion ,   Stack _ MinorVersion ) ;

• Find the "StackServer" implementation and assign its proxy to the variable server:

server   =   _ somdFindServerByName ( SOMD _ ObjectMgr ,   & e ,   " StackServer " ) ;

This causes the creation of the server proxy object in the client process. Proxy objects are shown as shaded circles. Note that the "real" server object in the server process is not created at this time. In fact, the server process has not yet been started.

• Ask the server object to create a "Stack" and assign "Stack" proxy to variable stack.

stk   =   _ somdCreateObj ( server ,   & e ,   " Stack " ,   " " ) ;

This causes somdd, the DSOM daemon (which is already running) to activate the stack server process (by starting the "generic" server program). The stack server process, upon activation, creates the "real" SOMDServer object in the server process. The SOMDServer object works with the DSOM run time to create a local "Stack" object and return a "Stack" proxy to the client. (The details of this procedure are deferred until section 6.4, "Basic Server Programming".)

• Ask the "Stack" proxy to push 100 onto the remote stack:

_ push ( stk , & e , 100 ) ;

This causes a message representing the method call to be marshalled and sent to the server process. In the server process, DSOM demarshals the message and, with the help of the SOMDServer, locates the target "Stack" object upon which it invokes the method ("push"). The result (which is void in this case) is then passed back to the client process in a message.

• Invoke more "Stack" operations on the remote stack, via the proxy:

_ push ( stk , & e , 200 ) ;
_ pop ( stk , & e ) ;

if   ( ! _ empty ( stk , & e ) )   t   =   _ top ( stk , & e ) ;

• Explicitly destroy both the remote stack, the stack proxy, and the server proxy:

_ somdDeleteObj ( server ,   & e ,   stk ) ;
_ somdReleaseObject ( SOMD _ ObjectMgr ,   & e ,   stk ) ;

_ somdReleaseObject ( SOMD _ ObjectMgr ,   & e ,   server ) ;

• Free the error-passing environment:

SOM _ UninitEnvironment ( & e ) ;

This scenario has introduced the key processes in a DSOM application: client, server, and somdd. Also introduced are the key objects that comprise the DSOM run-time environment: the SOMD_ObjectMgr in the client process and the SOMD_ServerObject in the server process.