dit RMI-HRT: Remote Method Invocation for Hard Real Time Systems UPM D. Tejera, A. Alonso, M.A de Miguel Universidad Politécnica de Madrid

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1 RMI-HRT: Remote Method Invocation for Hard Real Time Systems D. Tejera, A. Alonso, M.A de Miguel Universidad Politécnica de Madrid JTRES 2007, Vienna 1

2 Introduction Provide support for the development of Distributed Hard Real-Time Systems with Java There is an industrial need for such support RTSJ (Real-Time Java Specification): Defines extensions for RTS No support for distribution (JSR-50) No support for hard real-time systems (JSR-302) RMI-HRT: Oriented to Hard Real-Time Systems Available RMI implementations are not suitable DIT/

3 HRTJ: Hard Real-Time Profile Reliable and predictable Java concurrent model Main features: Schedulable objects: periodic or sporadic with MIT Only no-heap RTSJ objects Application executes in two phases:» Initialization: load and creation of required elements» Mission: execution of business code Limited memory model to achieve predictability:» No object creation on immortal during mission phase» Each SO has its own scoped memory Defined in HIJA project and one basis of JSR-302 DIT/

4 RMI-HRT Compliant with HRT profile Time and memory predictability Off-line schedulability and memory analysis RMI model has been simplified System configuration is known in advance Resource needs, release parameters, activation patterns, invocation patterns, etc. DIT/

5 RMI-HRT Two execution phases: Initialization and Mission Configuration parameters are modeled as classes, Static creation of threads, connections, etc. References: Each one is associated with one connection Characterized by a set of real-time parameters New serialization approach Memory usage: Scope memory for temporal objects Immortal memory for initialization and keeping state DIT/

6 Initialization Phase Node 1 Client1 2. new stub( Ref1 ) L Node 2 Server Hrt-Stub Client2 H1 m1 m2 1. Initializer: Creation of basic objects HRT Remote Object 2. Connection creation and parameter passing 3. Handler creation and associated to a connection and remote object DIT/

7 Mission Phase Node 2 Node 1 ref 1 L Server Client m1() 4 9 Hrt-Stub 8 7 H1 6 Hrt-Skel 5 m1 m2 HRT Remote Object DIT/

8 Predictable Serialization Relies on the static nature of HRT applications: a-priori knowledge of communicating objects RMI compiler performs preliminary activities to simplify run-time serialization Calculates the worst-case objects size Generates classes for serialization operations At run-time: Internal buffers are created at initialization phase No need for creating objects during mission phase The knowledge of worst-case streams size is used for a precise end-to-end response time calculation DIT/

9 Response Time Analysis System composed by a set of transactions Transactions composed by a set of actions An action is a portion of code in a thread or a message Actions can only be activated by an event which can only activate an action Linear action e i j-1 e i j+1 a j T i j-i = T i = T i j+1 CPU-1 Net CPU-2 e 1 e 1 2 e 2 3 a 1 a 2 a 3 DIT/ 9

10 Memory Usage Client RMI-HRT Core RMI-HRT Core Server Client IM 1 Hrt-Stub IM 2 Serialization Classes Net Module B1 B2 Net Module B3 B4 Handler IM3 Hrt-Skel IM4 Serialization Classes Remote Object IM5 Scoped Memory ReturnValue Scoped Memory Parameters Temporary Objects IM = Immortal memory, Bx = Buffer x DIT/

11 Industrial Assessment DIT/

12 Conclusions RMI-HRT allows development of DHRTS Compliant with HRTJ profile Its design and implementation allows for memory and time response predictability Future work: Further experimentation Precise characterization of memory usage and overhead in an industrial platform Other improvements: serialization, error handling, etc Alignment with future standards DIT/

Recommendations for a CORBA Language Mapping for RTSJ

Recommendations for a CORBA Language Mapping for RTSJ CORBA Language Mapping Victor Giddings Objective Interface Systems victor.giddings@ois.com Outline Real-time Specification for Java Background Memory Management Thread Types Thread Priorities IDL to RTSJ