No Heap Remote Objects for Distributed real-time Java
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This document proposes a No Heap model for remote objects in distributed real-time Java systems. The model avoids garbage collection by containing objects within scoped memory areas. Remote objects have a creation context in immortal memory and invocation contexts in local temporary memory areas. This allows safe nesting of contexts by forbidding references from creation to invocation contexts while allowing references the other way. The model is compared to traditional garbage collected remote objects, showing it uses less time as it avoids garbage collection overhead.
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No Heap Remote Objects for Distributed real-time Java
- 1. No Heap Remote Objects for Distributed Real-Time Java Pablo Basanta-Val, Marisol García-Valls, and Iria Estévez-Ayres mailto:pbasanta@it.uc3m.es †Jornadas de Tiempo Real 2011- Madrid( ) Publicado en ACM Transactions On Embedded Systems
- 2. Outline • Context and Motivation • No-Heap Remote Objects – Basic Model • Programming model • Example • Performance – Extended Model • Programming patterns • Extended model • Performance • Conclusion and ongoing work 2
- 3. Memory management for real- time Java • Techniques used for memory management in real-time Java (RTSJ) – Auto-managed memory (object pools) – Garbage collection (and its RT* variants) – Regions (ScopedMemory) • Memory management issues in distributed real-time Java (DRTSJ) – Real-time garbage collection – Distributed Garbage Collection – Regions • Current garbage collectors may be not enough for distributed real-time applications – E.g. a heap with 1Gb may introduce a 30 seconds delay JRT-11 3
- 4. State of the art Denomination Technologies Goals RT- CORBA+ Implementation of RT-CORBA with RTSJ RTZen RTSJ DRTSJ RMI+RTSJ A specification for distributed real-time Java RT-RMI-York RMI+RTSJ A framework for distributed real-time Java. RT-RMI-UPM RMI+RTSJ Profiles for distributed real-time Java DRTJava-on-CSP CSP+Java Produce an alternative based on CSP formalisms RTJ-COM RTSJ A component framework for embedded Java Scratchpad RTSJ A no-heap component model for real-time Java A distributed real-time object-oriented platform APICOM RTSJ +CAN • There is not a simple technique to remove the GC’s from the server side !!! • RTZen hybrid approach, • DRTSJ , RTRMI-York, RTRMI-UPM take non-heap as a requirement JRT-11 4
- 5. RTSJ region-based memory model • Three types of memory areas :O1=new Object – Heap – Immortal Memory (I) – Scoped Memory (Sx) O1 • A selector mechanism Sa 1 – One scope stack per thread – Enter, executeInArea Sb O2 1 • Destruction mechanism I – Stack discipline (counter) • Safety mechanism Scope Stack – Assignment rule – Single parent rule Forbidden assignment Default allocation 5 context
- 6. Calculator() Calculator() NhRo: memory model lastInteger lastInteger add() add() lastResult() lastResult() doNothing() doNothing() • Fragmented memory model – Creation Context • Represents the state of the remote object – Invocation Context • Objects created during remote invocation • Safe nesting of contexts – NhRo-rule: references from creation to invocation are forbidden – References from invocation to creation are allowed 6
- 7. NhRo: Example JRT-11 7
- 8. NhRo: Impact on the middleware Scoped or Immortal CalculatorImpl_Stub CalculatorImpl lastInteger add() add() lastResult() lastResult() doNothing() doNothing() Programmer Layer ObjId Ref CC Invocation max Invocation 1 CalcID Immortal memory 0 0 Remote Object Table Thread Memory Area Pool Pool Middleware Layer JRMP/IIOP Transport Transport RTSJ Virtual Machine Client Server 8
- 9. NhRo in action Calculator() Creation Context lastInteger (Immortal Memory) add() lastResult() Invoc. Context doNothing() (LTMemory) CalcID Ref OBJId Table enter 0 0 1 0 Thread Memory Area objID a b pool pool meth tmp ser 1 Transport CalcID.add(DataInt(3),DataInt(4)) Middleware Program DataInt(7) created created object object 9
- 10. NhRo vs. traditional GC’d remote objects Garbage collector RTSJ-RI Memory area pool Garbage collector RTSJ-RI Memory area pool 8 16 7 14 6 Consummed time (ms) 12 Consummed time (ms) 5 10 4 8 3 6 2 4 1 2 0 0 1 21 41 61 81 101 121 141 752 1286 1910 2534 3158 sample Alive memory (kB) JRT-11 10
- 11. Enhancements to the basic NhRo model • Patterns for programming with NhRos • NhRo stored in scoped memory – Scope stack characterization – Changes in the middleware – Policies for the memory are pool • Performance issues – Dependency on data transmitted JRT-11 11
- 12. Calculator() NhRo: constraints (I) lastInteger add() lastResult() doNothing() • NhRo-rule limitations – Objects is creation context are destroyed after remote invocation by default • Two patterns to avoid the problem – Copy pattern – Extended portals 12
- 13. NhRo: Scope Stack at the server Invocation context :RO1=new RemoteObject Sinv1 a b Handler 1 Thread Sa RO1 Sa RO1 Creation context Creation context 1 1 Sb Sb 1 1 I I Scope Stack Scope Stack (during remote object creation) (during remote invocation) • Creation context: state of the remote object • Invocation context: parameters of remote invocation 13
- 14. Decoupling middleware implemenation from NhRos JRT-11 14
- 15. Invocationnumber Memory Area Pool Invocationsize 0 0 0 Memory Area • It stores LTMemory instances only Pool • It requires two configuration parameters – Number of instances in the pool – Memory associated to each invocation context • Auto-collection – Invocation context returns automatically to its pool when they are not used • Internal counter 1→0 • Avoids memory area leakage 15
- 16. bytes 5000 0 10000 15000 20000 25000 30000 void boolean byte char short int long float double null Byte Short Integer Long Float Double Character X Boolean RtUnRemOb String() JRT-11 String(10) and LTMemory size String(25) String(50) String(100) Object[0] Object[10D] Object[25D] Object[50D] Object[100D] Vector(0) Vector(10D) Vector(25D) Vector(50D) Vector(100D) Remove invocation parameters X echo(X) X doNothing() void doNothing(X) 16
- 17. NhRos vs. (RT*) Garbage Collectors [new] JRT-11 17
- 18. Conclusions • This work has introduced a model able to remove the garbage collection from the end-to-end path – NhRo model • Empirical results showed: – Its implementation in basic environments is simple – The performance patterns offered are powerful JRT-11 18
- 19. Ongoing Work- • To produce an analytic model for the NhRo – Use of heap, and different threads – Identification of useful combinations • Analyze the parentage-rules proposed by Higuera- Toledano and integrate them with NhRos – A more restricted model JRT-11 19
- 20. JRT-11 20
Editor's Notes
- #7: From the programmer perspective, the memory model of the region based remote objects, the memory is fragmented is fragmented in two contexts. The first of this contexts is the creation context The creation context contains all objects that are accessible from the remote object instance; that is, all objects that are accessible from the state of the attibutes. The second of the contexts is the invocation context. The invocation context contains all objects that are created as consequence of the remote invocation. All objects created in the remote methods of the object belongs to the invocation context. Besides there is a safety rule. This rule is kown as NhRo-rule. It states that the objects created during the remote invocation may not be references from those that belonging the creaation context. The opposite is posible, an object stored in creation context may be referenced from the creation context.