Böge, M

Chrin, J

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A CORBA BASED C LIENT-SERVER MODELFOR B EAM D YNAMICS A PPLICATIONS AT THE SLSM. Bo¨ge , J. Chrin   Paul Scherrer Institut, 5232 Villigen PSI, Switzerlandemail: Michael.Boege@psi.ch email: Jan.Chrin@psi.chAbstractA distributed object oriented client-server model, basedon the Common Object Request Broker Architecture(CORBA), has been established to interface beamdynamics application programs at the Swiss Light Source(SLS) to essential software packages. These includethe accelerator physics package, TRACY, the CommonDEVice (CDEV) control library, a relational databasemanagement system and a logging facility for errormessages and alarm reports. The software architectureallows for remote clients to invoke computer intensivemethods, such as beam orbit correction procedures, ona dedicated server running the UNIX derivative, Linux.Client programs typically make use of graphical userinterface (GUI) elements provided by specialized toolkitssuch as Tk or Java Swing, while monitored data requiredby procedures utilising the TRACY library, such asbeam optics parameters, are marshalled to the modelserver for fast analysis. Access to the SLS acceleratordevices is achieved through a generic C++ CDEV server.The architectural model components are describedand a prototype application within the beam dynamicsenvironment is presented.1 INTRODUCTIONThe Swiss Light Source (SLS) [1] is a 2.4 GeV electronstorage ring currently under construction at the PaulScherrer Institute, Switzerland. Electrons from aninjector booster synchrotron, fed by a 100 MeV linearaccelerator, are transferred to the main ring at fulloperating energy. Scheduled for operation in August2001, the SLS will provide synchrotron radiation of highbrilliance to experimenters from a variety of disciplines.A considerable number of high-level beam dynamicsapplication program interfaces (APIs) are required forthe commissioning and operation of the SLS acceleratorcomplex and for machine physics studies. These APIstypically share a number of generic tasks including: access to an accelerator physics package, accelerator device control, database access and management, and logging of error messages and alarms.With the aid of object-oriented methodology, commonfunctions can be identified and developed as reusablecomponents. Furthermore, a distributed system allowsoptimal use of available resources, an importantconsideration given the computer intensive physicsalgorithms employed by the accelerator modellingprocedures. To this end, a distributed client-servermodel, based on the Common Object Request BrokerArchitecture (CORBA) [2], is presented; client programsreadily access shared services, either locally or across thenetwork, through CORBA objects.2 ARCHITECTURAL MODELIn the evolution of object-oriented distributed computingsystems, CORBA is a recent standard that provides amechanism for defining interfaces between distributedcomponents. Its most distinguished assets are platformindependence, in so far as the platform hosts a CORBAObject Request Broker (ORB) implementation, andlanguage independence, as ensured through the use of theInterface Definition Language (IDL). The latter featureis of particular interest to SLS beam dynamics APIdevelopers as it provides for the option between high-levelapplication languages. For instance, the client componentof the prototype closed orbit correction API has beenimplemented in Tcl/Tk [3] using the BLT extension, apackage that is an appropriate match to the requirementsof this particular application. The server components, onthe other hand, have been implemented in C++ for highperformance and run on a dedicated server machine. It isinteresting to note that in this multi-language scenario,the Tcl/Tk client program is comparatively short in lengthand, therefore, quite managable. Optimal use of theTk/BLT package is made for building the graphical userinterface (GUI) component of the API, while the morecomplex components are routed to server processes bymeans of CORBA objects.2.1 Server Hardware and System SoftwareComponentsThe chosen operating system and platform for serverapplications is RedHat Linux version 6.0 on a serverhousing dual 550 MHz Intel Pentium III processors.The use of Linux and the GNU project C++ compilerInternational Conference on Accelerator and Large Experimental Physics Control Systems555International Conference  Accel rator and L rge Experim ntal Physics Control Systems, 1999, Trieste, ItalyGUI    TRACYModel ServerTcl/Tk  or Javaclient  API     Local Control SystemCDEVServerMonitor Control    Analysis     Server   Database    ServerDatabase   Message    Se r ver     All processesFigure 1: Software Architectural Model for SLS Beam Dynamics APIs(egcs) avoids vendor dependency; compilation with egcsfurther reduces the dependency on the operating systemthereby increasing the portability of applications. Asecond identical server is permanently available to provideredundancy. Client programs typically run on local LinuxPCs.The principal CORBA product employed is MICO [4],a fully compliant CORBA 2.2 implementation, availablefree of charge under the GNU public license terms.Use is made of the Naming Service and InterfaceRepository facilities provided by MICO. Significantly,in addition to the given IDL to C++ mapping, a Tclinterface to MICO [5] that provides CORBA client andserver functionality to Tcl scripts has been incorporated.Noticably absent from MICO at present, however,is mapping for the Java programming language [6].Since Java client components will be an integral partof SLS beam dynamics applications, another CORBAproduct, namely the Java-based JavaORB package [7],provides IDL mapping to Java. Applications involvingpermutations of client-server processes written in C++,Tcl/Tk and Java have all been tried and tested, furtherverifying the interoperability between the differentCORBA 2-compliant products1.2.2 Server-Client Software ComponentsFig. 1 illustrates the conceptual design of the softwaremodel employed for the retrieval, analysis and display ofpertinent data for a specific beam dynamics API, namelythe closed orbit display. The prototype Tk/BLT client GUIis shown in Fig. 2.A CORBA interface to the C-based TRACY library [8]1Interoperability is made possible by virtue of the CORBA2.0 requirement that the Internet Inter-ORB Protocol (IIOP) bethe standard protocol for communication between ORBsprovides users with convenient access to the acceleratorphysics routines. This capability in itself provided strongmotivation for the use of CORBA as it allows access tothe same machine model as used in offline simulations;procedures tested in simulation can thus be effectivelyemployed for the optimization of the accelerator online.In this present example, measured beam positions aremarshalled to the dedictated TRACY model server foranalysis. A new set of corrector values is calculatedand presented to the client together with the predictedorbit. The corresponding hardware settings required toachieve the improved orbit are handled by the Analysisand Database Servers.Synchronous and asynchronous interaction with theEPICS-based local accelerator device control system [9]is achieved through use of the Common DEVice (CDEV)C++ class library (version 1.6.2) [10]. A generic CDEVServer employs a CORBA server object that respondsto CDEV-type verbs. The “set”, “get” and “monitor”verbs are accompanied by a CORBA sequence of objectscontaining the parameters required to, respectively,download setpoints, readback device attributes andmonitor selected channels. The configuration informationis held in a SQL92 compliant relational database [11]which is accessed through a CORBA wrapped DatabaseServer. The Analysis Server further retrieves monitoreddata from the real-time system, through the CDEV Server,for recalibration and analysis. The application APIembedded in the client GUI component polls the AnalysisServer for updated values and displays them.All client-server processes are able to report errormessages and alarms to a dedicated Message Serverthrough a CORBA interface. Presently the server employsthe UNIX syslog message logging facility, incorporatinga variety of priority levels. Syslog entries are furtherconverted to SQL insert queries for immediate entry into556Figure 2: A prototype client application displaying measured beam positionsthe database. Error messages are viewed either through aTcl/Tk based browser or the native database browser.The server-client components featured are typical ofthe requirements of several anticipated applications. Theframework further allows for critical code components tobe better tested through their eventual use in different APIs.3 FUTURE DEVELOPMENTSThe model presented here represents work in progressand, as such, a number of developments are foreseen.Since several of the servers have write privileges tosensitive software and hardware channels, it is intended toadd authentication procedures that identify and authorizethe client, e.g. through use of the Secure Sockets Layer(SSL), a protocol also supported by MICO. Serverdiagnostic tools will also be added to provide a synopsisof usage and performance.It is envisioned that configuration, calibration and otherdata will be held in an Oracle database. Work is in progresswithin the CDEV community to interface Oracle to theCDEV service layer allowing easy database access throughthe CDEV device/message paradigm [12].Of the CORBA facilities and services that are becomingincreasingly available, particularly appealling is the EventService which offers a convenient channel for distributingdata to one or more consumers. Data from a supplieris distributed to consumers, on a push or pull basis,without the supplier requiring knowldege of the receivingobjects. Such a service would be usefully employed in thedistribution of calibrated data to client consumers.The use of Java is noticably gaining momentum inthe accelerator physics community; its unique featuresof garbage collection, exception handling and integratedthread support are desirable assets for building large-scaledistributed systems. Java Swing and Java Beans furtheroffer components for building GUI operator interfaces(OPIs). In this respect, an effort to coordinate activitieswith the aim of releasing a standard Java OPI is on theSoftware Sharing Workshop agenda [13].4 CONCLUSIONAn object oriented client-server model in which dedicatedC++ servers provide essential services to clients by meansof CORBA objects has been presented. A prototypeclient application has demonstrated that the proposedarchitectural model offers an appropriate framework forapplication programmers to develop APIs within the beamdynamics environment.5 REFERENCES[1] M. Bo¨ge et al., “The Swiss Light Source AcceleratorComplex: An Overview”, Proc. 1998 6th European ParticleAcc. Conf. (EPAC-98), Stockholm, Pub: IoP, UK, p. 623[2] OMG, CORBA, http://www.omg.org/[3] J.K. Ousterhout, “Tcl and the TK Toolkit”, Pub: Addison-Wesley; Tk/BLT, http://www.tcltk.com/blt/[4] A. Puder, K. Ro¨mer, “Mico is CORBA”, Pub: ApProfessional; http://www.mico.org/[5] F. Pilhofer, “TclMico, A Tcl Interface to Mico”, http://www.informatik.uni-frankfurt.de/˜fp/Tcl/tclmico/[6] Java, http://java.sun.com/[7] JavaORB, http://www.multimania.com/dogweb/Projects/JavaORB/javaorb.html[8] J. Bengtsson, “TRACY-2 User’s Manual”, SLS InternalDocument (1997); M. Bo¨ge, “Update on TRACY-2Documentation”, SLS Internal Note, SLS-TME-TA-1999-0002 (1999); http://slsbd.psi.ch/pub/slsnotes/[9] M. Dach et al., “Control and Data Acquisition System of theSwiss Light Source”, ICALEPCS’99, Invited Paper MA1I01[10] CDEV, http://www.jlab.org/cdev/[11] PostgreSQL, http://www.pgsql.com/[12] W. Watson, T. Pal, private communication[13] SOSH’99, http://www.jlab.org/sosh/sosh99/557

A CORBA Based Client-Server Model for Beam Dynamics Applications at the SLS

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