2/9/20101Remote Batch Invocation for Compositional Object ServicesCPS 296.19thFeb 2010Vamsidhar ThummalaContent borrowed from William R CookStandard Approach to Distribution` Step I: Design a language` Clean Interfaces, modules` Step 2: Add library for distribution` Remote procedure calls` Stub that send calls remotely` Distributed objects` C, C++, ML` RMI` CORBA` DCOM` Proxies: pointer to remote object` Create proxies on demand` End Result` Clean, elegant, orthogonal` Is it the case for Persistence too?` Example in later slides` Cons?` PerformanceExample: Music Jukebox in the Cloud` Remote service which can play music on your home speakers` Fine-grained interface` OO designinterface Music {Album[] getAlblums();…..}interface Alblum {String getTitle();void play();int rating();….}Remote Procedure Calls (RPC)int minimumRating = 4;Music musicService = ... ;for (Album album : musicService.getAlbums()) {if (album.rating() > minimumRating) {System.out.println("Played: " +album.rating() + " " +g()album.getTitle());album.play();} else {System.out.println("Skipped: " +album.getTitle());}}RPC behind the scenes Result: Too many RPC callsint minimumRating = 4;Music musicService = ... ;for (Album album : musicService.getAlbums()) {if (album.rating() > minimumRating) {System.out.println("Played: " +album.rating() + " " +g()album.getTitle());album.play();} else {System.out.println("Skipped: " +album.getTitle());}}n: number of albumsworst case: 4n + 1 remote calls2/9/20102Current approaches` Data Transfer Objects and Server Façade` Move data in bulk` Specialize to particular sequence of client calls` Document-oriented Web Services` Stateless servers` TCP-based command line interfaces` POP, IMAP, FTP, HTTP, etc...` End result` Messy, non-compositional, rigid … fastData Transfer Objectclass TitleAndRatingAndCond implements Serializable {public String getTitle() { ... }public int getRating() { ... }public boolean getCond() { ... }pg(){}}Remote Facadeinterface MusicFacade{TitleAndRatingAndCond[]TitleAndRatingAndCond[]playHighRatedAlbums(int minRating);...}Remote Façade and Data Transfer Objectsint minimumRating = 4;MusicFacade musicService = ... ;TitleAndRatingAndCond[] results =musicService.playHighRatedAlbums(minimumRating);for (TitleAndRating result : results) {if (result.getCond()) {(g()){System.out.println("Played: " +result.getRating() + " " +result.getTitle());} else {System.out.println("Skipped: " + album.getTitle());}}What are the problem with DTO and Remote Façade? ` Tight coupling with objects/code` Not service-oriented` Can result in ` under-approximation ` Multiple calls to server Client needs to print title of two different albums` over approximation` Single call to serverRemote Batch Invocation (RBI) - Insight` We have an incorrect assumption:` Distribution can be solved in existing languages without any changes` Goals` Fine-grained interfaces` Execute many remote operations in bulk` Create Facades and Transfer objects automatically2/9/20103Remote Batch Invocation (RBI)int minimumRating = 4;Service service = ... ;batch (Music musicService : service) {for (Album album : musicService.getAlbums())final Artist = musicService.addArtist(“John”);if (album.rating() > minimumRating) {System out println("Played:"+System.out.println( Played: +album.rating() + " " +album.getTitle());album.play();} else {System.out.println("Skipped: " + album.getTitle());}}}Generated Façade by Partitioningint minimumRating = 4;Service service = ... ; Music musicService = ...;for (Album a : musicService.getAlbums())if (a.rating() > minimumRating) {// GET rating, titlealbum.play();} else {}Remote}for (????) {if (???) {System.out.println("Played: " +rating + " " +title);} else {System.out.println("Skipped: " + title);}}LocalGenerated Codeint minimumRating = 4;Service service = ... ; Music musicService = ...;List<TitleAndRatingAndCond> results = new...;for (Album a : musicService.getAlbums())if (a.rating() > minimumRating) {results.add(new TitleAndRatingAndCond(a.rating(), album.getTitle(), true));album.play();} else {results add(newTitleAndRatingAndCond(0 null false);Remoteresults.add(new TitleAndRatingAndCond(0, null, false);}for (TitleAndRatingAndCond result : results) {if (result.getCond()) {System.out.println("Played: " +result.getRating() + " " +result.getTitle());} else {System.out.println("Skipped: " +result.getTitle();}}LocalRemote Batch Invocation` Clean server interface, decoupled clients` Fine-grained interfaces` Automatic bulk data transfer and facades` Only primitive values can be transferred between clients and server` No stubs, No proxies!`One round-trip per lexical batch block`One roundtrip per lexical batch block` Two kinds of exceptions:` Remote exceptions` Does the paper handle them? Not gracefully` Proposed solution: transactional memory on server Does this violate service-oriented (stateless) principle?` Network exceptions (reduced!)What can be executed remotely?` Sequences and Composition` batch (r) { r.foo(); r.foo().bar().getName(); }` Loops and Conditions` batch (music) {for (Album a : music.getAlbums() )if (a.rating() > 5)print( a.getName() + “: ” + a.rating() ); }What cannot be executed remotely?` Constructor calls` Casts` While loops` Assignments`Exceptions`Exceptions` Are these Java compiler specific?` What is the main drawbacks?` Think of SQL` Aggregate over collections cannot be done remotely2/9/20104RBI pros & cons – Memory model` Only transfer primitive values` No proxies (remote pointers)` Server can be stateless, “service oriented”` rbi.Service musicService = new rbi.Service(“MusicCloud”, Music.class);` What about iterative computation?` No distributed garbage collection` Serialization through public interfacesbatch (remote) {RemoteSet r = remote.makeSet();for (int elem : localSet().items() )r.add( elem );....}` Is it legal to set RemoteSet r = localSet?` Use public setters and getters` Need reusable helper functions/coercionsRBI pros & cons – Execution model` Client` Language support` How easy/hard is to add support to “batch” in PL?` final keyword` What about order of execution?` What is the output of the below code?StringBuilder sb = new StringBuilder();sb.append("My Album");batch(Music music : musicService) {m(sb);music.createAlbum("1", sb);}...void m(StringBuilder sb) { sb.append(": Blues"); }RBI pros & cons – Execution model` Client` Language support` How easy/hard is to add support to “batch” in PL?` final keyword` What
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