1CSE 120CSE 120Principles of Operating Principles of Operating SystemsSystemsFall 2004Fall 2004Lecture 14: Remote Procedure CallLecture 14: Remote Procedure CallAnd Network File SystemAnd Network File SystemGeoffrey M. VoelkerGeoffrey M. VoelkerNovember 22, 2004 CSE 120 – Lecture 14 – Remote Procedure Call 2© 2004 Geoffrey M. VoelkerWhy is RPC Interesting?Why is RPC Interesting?z Remote Procedure Call (RPC) is the most common means for remote communicationz It is used both by operating systems and applications NFS is implemented as a set of RPCs DCOM, CORBA, Java RMI, etc., are all basically just RPCz Someday (soon?) you will most likely have to write an application that uses remote communication (or you already have) You will most likely use some form of RPC for that remote communication So it’s good to know how all this RPC stuff works» More “debunking the magic”2November 22, 2004 CSE 120 – Lecture 14 – Remote Procedure Call 3© 2004 Geoffrey M. VoelkerClients and ServersClients and Serversz The prevalent model for structuring distributed computation is the client/server paradigmz A server is a program (or collection of programs) that provide a service (file server, name service, etc.) The server may exist on one or more nodes Often the node is called the server, too, which is confusingz A client is a program that uses the service A client first binds to the server (locates it and establishes a connection to it) A client then sends requests, with data, to perform actions, and the servers sends responses, also with dataNovember 22, 2004 CSE 120 – Lecture 14 – Remote Procedure Call 4© 2004 Geoffrey M. VoelkerMessagesMessagesz Initially with network programming, people hand-coded messages to send requests and responsesz Hand-coding messages gets tiresome Need to worry about message formats Have to pack and unpack data from messages Servers have to decode and dispatch messages to handlers Messages are often asynchronousz Messages are not a very natural programming model Could encapsulate messaging into a library Just invoke library routines to send a message Which leads us to RPC…3November 22, 2004 CSE 120 – Lecture 14 – Remote Procedure Call 5© 2004 Geoffrey M. VoelkerProcedure CallsProcedure Callsz Procedure calls are a more natural way to communicate Every language supports them Semantics are well-defined and understood Natural for programmers to usez Idea: Have servers export a set of procedures that can be called by client programs Similar to module interfaces, class definitions, etc.z Clients just do a procedure call as it they were directly linked with the server Under the covers, the procedure call is converted into a message exchange with the serverNovember 22, 2004 CSE 120 – Lecture 14 – Remote Procedure Call 6© 2004 Geoffrey M. VoelkerRemote Procedure CallsRemote Procedure Callsz So, we would like to use procedure call as a model for distributed (remote) communicationz Lots of issues How do we make this invisible to the programmer? What are the semantics of parameter passing? How do we bind (locate, connect to) servers? How do we support heterogeneity (OS, arch, language)? How do we make it perform well?4November 22, 2004 CSE 120 – Lecture 14 – Remote Procedure Call 7© 2004 Geoffrey M. VoelkerRPC ModelRPC Modelz A server defines the server’s interface using an interface definition language (IDL) The IDL specifies the names, parameters, and types for all client-callable server proceduresz A stub compiler reads the IDL and produces two stub procedures for each server procedure (client and server) The server programmer implements the server procedures and links them with the server-side stubs The client programmer implements the client program and links it with the client-side stubs The stubs are responsible for managing all details of the remote communication between client and serverNovember 22, 2004 CSE 120 – Lecture 14 – Remote Procedure Call 8© 2004 Geoffrey M. VoelkerRPC StubsRPC Stubsz A client-side stub is a procedure that looks to the client as if it were a callable server procedurez A server-side stub looks to the server as if a client called itz The client program thinks it is calling the server In fact, it’s calling the client stubz The server program thinks it is called by the client In fact, it’s called by the server stubz The stubs send messages to each other to make the RPC happen “transparently”5November 22, 2004 CSE 120 – Lecture 14 – Remote Procedure Call 9© 2004 Geoffrey M. VoelkerRPC ExampleRPC ExampleServer Interface:int Add(int x, int y);Client Program:…sum = server->Add(3,4);…Server Program:int Add(int x, int, y) {return x + y;}z If the server were just a library, then Add would just be a procedure callNovember 22, 2004 CSE 120 – Lecture 14 – Remote Procedure Call 10© 2004 Geoffrey M. VoelkerRPC Example: CallRPC Example: CallClient Program:sum = server->Add(3,4);Server Program:int Add(int x, int, y) {}Client Stub:Int Add(int x, int y) {Alloc message buffer;Mark as “Add” call;Store x, y into buffer;Send message;}RPC Runtime:Send message to server;Server Stub:Add_Stub(Message) {Remove x, y from bufferr = Add(x, y);}RPC Runtime:Receive message;Dispatch, call Add_Stub;6November 22, 2004 CSE 120 – Lecture 14 – Remote Procedure Call 11© 2004 Geoffrey M. VoelkerRPC Example: ReturnRPC Example: ReturnClient Program:sum = server->Add(3,4);Server Program:int Add(int x, int, y) {}Client Stub:Int Add(int x, int y) {Create, send message;Remove r from reply;return r;}RPC Runtime:Return reply to stub;Server Stub:Add_Stub(Message) {Remove x, y from bufferr = Add(x, y);Store r in buffer;}RPC Runtime:Send reply to client;November 22, 2004 CSE 120 – Lecture 14 – Remote Procedure Call 12© 2004 Geoffrey M. VoelkerRPC MarshallingRPC Marshallingz Marshalling is the packing of procedure parameters into a message packetz The RPC stubs call type-specific procedures to marshal (or unmarshal) the parameters to a call The client stub marshals the parameters into a message The server stub unmarshals parameters from the message and uses them to call the server procedurez On return The server stub marshals the return parameters The client stub unmarshals return parameters and returns them to the client program7November 22, 2004 CSE 120 – Lecture 14 – Remote Procedure Call 13© 2004 Geoffrey M.
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