RPC

Remote Procedure Call

• Client-Server provides a mechanism for services in distributed systems BUT
  • requires explicit-communication (send-receive)
• How do we make distributed computing look like normal?
• Can we use procedure calls?

Parameter Passing

• RPC has to pass parameters
• RPC can simulate through
  • Stubs – proxies
  • Marshaling
• What about globals?

Stubs

• Client makes a procedure call to the client stub
• Defined from an IDL (Interface Definition Language)
• Stubs take care of the marshaling and sending over the network
• Marshaling – Packaging of the arguments

RPC View

RPC Steps

• Client call stub
• Client Stub does marshalling
• Client OS sends to Remote OS
• Server stub unpacks params
• Server does work and returns to stub
• Server stub does marshaling
• Server OS sends to Client OS
• Client OS gives to Client stub
• Client Stub unpacks and returns to app

Problems in Marshalling

• Different machines can have different archs and data formats
  • i.e.: little endian, SPARC: big endian
• How do we pass pointers
  • What it it points to a struct
  • What if it points to a struct with pointers
• Marshalling transforms the params into a byte stream

Failure Semantics

• Server can crash, client can crash, etc.

Client and Server should be cognizant of these failure semantics.

SUNRPC - Binder: Port Mapper

• On start up, the server creates port.
• Server stub calls svc_register to register program #, version #, with local port mapper.
• Port mapper stores prog #, version #, and port.
• On start up client will call clnt_create to locate the server port
• Upon return, the client can now call procedures on the server.

RPCGEN Example