Windows NT Systems Programming

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RPC Postscript

Running Second Version (Revised)

(code is here)

Server Program

• Create server project as console application
• Import ccrpc2.idl, mandels2.cpp
• Run midl on ccrpc.idl to generate
  • Either use console window and type command "midl ccrpc.idl"
  • Or import into project (created below) and in Project/Settings, custom build with the command
    midl $(InputPath)
    and the output file(s):
    $(ProjDir)\$(InputName).h
    $(ProjDir)\$(InputName)_s.c
• Import ccrpc2.h, ccrpc2_s.c (generated by midl)
• Change project settings to add to the Link tab the libraries "rpcrt4.lib" and "rpcns4.lib"
• In "ccrpc.cpp", change the line
      for (x=left, i=0; x<=right; x += xstep, i++)
  to the line
      for (x=left, i=0; i<width; x += xstep, i++)
  (the old line wrote beyond the end of the line array)
• Build project

Client Program

• Create client project (could open another VC++) as a win32 application
• Add files mandelc2.cpp mandelc2.rc, menus.h
• If using custom build for midl, in Project/Settings, custom build with the command
  midl $(InputPath)
  and the output file(s):
  $(ProjDir)\$(InputName).h
  $(ProjDir)\$(InputName)_c.c
• Add files ccprc2.h, ccrpc2_c.c
• Add two libraries above
• Change general settings to use MFC in shared DLL
• added #include "memstub" to mandelc2.cpp
• build project

ccrpc2.idl

[
  uuid (87654329-4321-1234-4321-987654321CBA),
  version(1.0),
  endpoint ("ncacn_np:[\\pipe\\ccrpc2]")
]
interface calcline
{
  typedef struct
  {
    double real;
    double imag;
  } complex;

  void CalcLine([in] double left, 
	[in] double right,
	[in] double y, [in] long width,
	[out, size_is(width)] short line[]);
}

Memory Allocation (MEMSTUB)

void __RPC_FAR * __RPC_API
	midl_user_allocate(size_t len)
{
	return(new(unsigned char [len]));
}

void __RPC_API midl_user_free(void __RPC_FAR * ptr)
{
	delete(ptr);
}

RPCs and Objects: Towards a distributed object model

• RPCs work well for stateless functions which do not access any environment specific functions/variables
  Stateless IN and stateless OUT
• If the member functions of an object are truly stateless, then there is no problem in distributing.
• HOWEVER, one the main rationales for object is that they encapsulate both functions and state.
• While member functions belong to the class, the variables belong to an object
• In addition to naming the state variable, one must also name the object containing that variable.
• Unlike function names, Objects names are created dynamically
• Object creation implies a client name, server name and a way to resolve the two dynamically
  • The constructor could hide much of this by creating a Object shell
    which knows the name of the real object living on the server
    e.g. CMessage msg;
    • Create an Object "shell" (analogous to a function stub) which contains the member function stubs and appropriate state information about the remote object.
    • calls server to create a new object and return its name which is stored in shell as a state variable.
• Each member function call (RPC)  uses the stub in the object shell which also adds the server object name so that the proper server object is accessed
• Changes to the object state are made on the server.
• Must disallow direct access to the data members of an object (only private data members) or keep a copy of these variables in the shell (there will be some synchronization issues).

Copyright chris wild 1997.
For problems or questions regarding this web contact [Dr. Wild].
Last updated: November 03, 1997.