CSE 358 Spring 2006 Selected Notes Set 8

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1 CSE 358 Spring 2006 Selected Notes Set 8 Alexander A. Shvartsman Computer Science and Engineering University of Connecticut February 2,

2 - Models Centralized (e.g, single node) system C-S is implemented as a local procedure call Request becomes input arguments Response are the output arguments No messages -- no unreliability attributable to network Distributed system: consider several alternatives Traditional approaches Remote procedure call Network objects -- Object call

3 - Models: Distributed Systems -server a-la maman Use send / receive primitives Implement client-server interactions manually (message discipline, message syntax/semantics) Remote procedure calls (RPC) Extending local procedure call to remote call Formally specifying input/output arguments Letting the RPC framework do the low level work Network objects Modeling servers formally in terms of objects Taking advantage of object-oriented features Letting the object framework do the low level work Object Request Broker (ORB) technology

4 Remote Procedure Call (RPC) Using a procedure call paradigm to implement distributed - Request / Reply protocol Maintain procedure call simplicity Provide distribution transparency call call

5 An Example Problem Consider main() { long A[1024]; long B[1024]; long result; char nonnegative; char inner();... nonnegative = inner(1024, A, B, &result);... char inner ( long size; long A[]; long B[]; long *result ) { long i; *result = 0; for (i=0; i<size; i++) *result += A[i]*B[i]; return(*result >= 0); } }

6 Remoting the Call (1) Memory and addressing main s stack frame inner s stack frame &result B A size return address saved registers i Remoting the call main s stack frame on local computer inner s stack frame on remote computer &result B A size return address saved registers i

7 Deploying stub routines Remoting the Call (2) main s stack frame client s stub stack frame &result B A size return address server s stub stack frame inner s stack frame &result B A size return address saved registers i Stack on client / local computer Stack on server / remote computer

8 Identifying and Specifying an Interface Interface Definition Language (e.g., DCE/IDL) Disambiguating data types Input / Output parameters Array sizing Pointers [ type ); (e.g., Idempotent) } and endpoint ] Interface identification and versioning Stubs s and servers [uuid (A01A D C000111), version (3.1.)] interface vectorops { small inner ( [in] long size, [in, size_is (size)] long A[], [in, size_is (size)] long B[], [out] long *result

9 What Goes Over the Wire Stubs and argument marshalling, I.e., encoding/decoding Flatten data structures for transmission Manage data representation Transfer syntax -- (e.g., NDR, network data representation) STUB marshal unmarshal wire A[1..size] B[1..size] wire STUB unmarshal inner marshal result return value CLIENT SERVER

10 Locating s Direct binding and server agreement, out of band deploys direct identification/addressing Easy to deal with for simple applications Inadequate for complex systems Name Service s export interfaces and binding info to a name service s query the name service and import info import import Name Service export export export

11 Building RPC and Components to be developed: IDL file, client and server Stubs are automatically generated and server are built for each platform IDL FILE IDL Compiler Code Stub Stub Init. Code Linker Run-time Libraries Linker

12 RPC - Big Picture Do RPC Find a compatible server Connect to the server Marshal arguments and form network packets Send input arguments... wait Receive the results Process network packets, unmarshal results Pass the results to the calling code Handle exceptions (if any) Select network protocols Advertise RPC interfaces and services in name service Listen for calls... wait Receive the call Process network packets and unmarshal arguments Create server context Invoke called procedure Execute remote procedure Marshal output arguments and form network packets Send the results

Distributed Systems 8. Remote Procedure Calls

Distributed Systems 8. Remote Procedure Calls Paul Krzyzanowski pxk@cs.rutgers.edu 10/1/2012 1 Problems with the sockets API The sockets interface forces a read/write mechanism Programming is often easier