Report from theRequirements Group forReal-time ExtensionsFor the Java™ PlatformLisa Carnahan, NISTEditorU.S. DEPARTMENT OFCOMMERCETechnology AdministrationInformation Technology LaboratoryNational Institute of Standards andTechnologyGaithersburg, MD 20899-0001NISTIR XXXX - WORKING DRAFTOctober 28, 1998Requirements For Real-time ExtensionsFor the Java™ PlatformThe Requirements Group for Real-time Extensions to the Java™ Platform includes representativesfrom companies and organizations whose expertise spans the computing industry and academia. Industryparticipants include desktop, server, and enterprise systems providers, embedded systems providers,device manufacturers, and real-time operating system vendors. The goal of the Group is to develop cross-disciplinary requirements for real-time functionality that is expected to be needed by real-timeapplications written in the Java™ language and executing on various platforms. Seehttp://www.nist.gov/rt-java for more information regarding the Requirements Group and thisdocument.Members of the Requirements Group for Real-time Extensions to the Java™ Platform include:Access Co., Ltd.Ada Core Technologies, Inc.AonixApogee SoftwareBay Networks / Bay Architecture LabCommotion Technology, Inc.Enea OSE SystemsFlorida State University, Department of ComputerScienceHewlett-Packard CompanyHoneywellIBMInsignia Solutions, Inc.Integrated Systems, Inc.Intermetrics, Inc. (An AverStar Company)Mantha Software, Inc.MicrosoftMicroware Systems CorporationMotorola, Inc.NewMonics, Inc.NIST/Information Technology LaboratoryNokia ResearchNSI ComOberon MicrosystemsOMRON CorporationPlum Hall, Inc.Plum Hall Europe, Ltd.QNX Software Systems, Ltd.Rockwell CollinsSchneider AutomationSiemens AG, A&DSilverhill Systems, Inc.SoftPLC CorporationSun Microsystems, INC.TeleMedia Devices, Inc.The MITRE CorporationThe Open GroupWind River Systems, Inc.TM: Java and all Java-based trademarks and logosare trademarks or registered trademarks of SunMicrosystems, Inc. in the United States and othercountries.- i -Table of ContentsSection 1 - Terms and Concepts..................................................................................................1Real-time Concepts.................................................................................................................1Real-time Scheduling..............................................................................................................1Negotiating Component ..........................................................................................................2Terms......................................................................................................................................2Sources...................................................................................................................................4Section 2 Java(tm) Traits..............................................................................................................4Section 3 Guiding Principles......................................................................................................5Section 4 Goals and Derived Requirements................................................................................5Section 5 Resource Management (RM) Requirements................................................................7Introductory Discussion ..........................................................................................................7Utility of Resource Management:............................................................................................8Derived Requirements.............................................................................................................8Open Issues.............................................................................................................................9Section 6 Requirements for Memory Management (MM) ........................................................10Introductory Discussion ........................................................................................................10Derived Requirements...........................................................................................................10Open Issues...........................................................................................................................11Section 7 Asynchrounous Event Handling................................................................................12WORKING DRAFT – OCTOBER 28, 1998 - 1 -Section 1 - Terms and Concepts Real-time ConceptsReal-time Computing has two aspects: ‘operating in real-time’ and real-time resource management. Asystem (at any level of abstraction -- e.g., application, computer system, operating system, Java platform,etc.) operates in real-time to the degree that it satisfies the system's time constraints acceptably -- i.e., withacceptable optimality and predictability. To that end, resource management is real-time to the degree thatit explicitly takes those time constraints into account. [Abstracted from Jensen]Timeliness can be defined by three aspects: (1) any time constraints (e.g., deadlines) on individualactivities (an activity is a portion of a thread's locus of execution); (2) the collective timelinessoptimization criterion used for scheduling threads to meet their activity’s time constraints (e.g., meet allhard deadlines, minimize the number of missed deadlines according to their relative importance,minimizise mean tardiness, etc.), (3) the trade-off between the collective timeliness optimality and thepredictability of that collective timeliness optimality value (e.g., mean tardiness or number of misseddeadlines may be higher but their variance is lower, or vice versa). [Abstracted from Jensen]Predictability is the degree to which something can be known a' priori. It implies the degree to which thefuture execution (system and application) context of that something can be predicted. Determinism andmaximum entropy are the end-points on the scale of predictability, and coefficient of variation is anexample of a predictability metric. [Abstracted from Jensen]Hard DeadlineA hard deadline is an activity time constraint which requires that the activity complete bythe deadline time in order to be considered timely; completion after the deadline is considered untimely(i.e., there is no utility in completing the activity). [Abstracted from Jensen]Hard real-time