Temadag om Java

JamaicaVMHard Realtime Response for Java Programs

Dr. Isabel Tonin CEO, aicas

September 2013

2JamaicaVM: Realt ime Response for Java Applications

Java Advantages

Deep Ecosystem

Large number of developers

Diverse middleware and libraries

Many development tools

Well defined language

Minimizes errors (strong typing w/ GC)

Security and memory model

Support for parallelism & distribution

Supports dynamic code loading (modules)

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Real-Time Specification for Java

Realtime Tasking

Realtime threads

Event handling

Priority inversion avoidance

Control Flow

Deadline Mon & Cntrl

Overrun Mon & Cntrl

ATC

Input/Output

Raw memory

POSIX events

Happenings

Memory Areas

Immortal

Scope

Physical

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Java Problemsunpredictable pauses & delays

Java nondeterminism

Java application size

Java performance

Java RTSJ Scoped Memory complexity

Lack of Java on Embedded Platforms

The JamaicaVM Solution

JamaicaVM SolutionMultithreaded, fully preemptable Garbage Collector (RTGC)

worst case execution time analysis (WCETA) possible with deterministic RTGC

Smart Linker reduces executable size by up to 90%

ahead-of-time (AOT) compiler delivers “native” compiled code performance

no need for ScopedMemory

support for most embedded OSes & CPUs including GENIVI

5JamaicaVM: Realt ime Response for Java Applications

Realtime Java Technology

Static compiler technology with profiling

Faster code

Better time vs. space trade off

Smart linking

Only include what is necessary

Deterministic garbage collection

GC does not interrupt other (realtime) tasks

No pauses in the application

6JamaicaVM: Realt ime Response for Java Applications

Determinist ic Garbage Collection

Saves development time

No need to release objects explicitly

Fewer memory errors

Improves safety

Reduces the danger of memory leaks

Prevents premature object deallocation

Does not interfere with realtime response

7JamaicaVM: Realt ime Response for Java Applications

Certifying a Garbage Collector

Not possible for all collector

Must be deterministic; no unbound steps

Must assume maximum memory use

Must consider allocation rate

Work Based Collector

No root scan and compaction (unbound)

Mark and sweep steps on fixed size blocks

Automatically tracks allocation rate

8JamaicaVM: Realt ime Response for Java Applications

Conventional Garbage Collection

GC can interrupt execution for long periods of time:

Problem

long, unpredictable pauses during execution

9JamaicaVM: Realt ime Response for Java Applications

RTSJ & Conventional Garbage Collection

No heap threads can interrupt garbage collector:

The application must be split into a realtime and a nonrealtime part.

10JamaicaVM: Realt ime Response for Java Applications

Realtime Garbage Collection

Paced garbage collectorRun GC at a high priority

Runs at given interval, for given amount of time

Programmer must provide both maximum memory use and maximum allocation rate

Slack garbage collectorRun GC at lower priority than realtime tasks

Runs when processor cycles are available

Programmer must provide both maximum memory use and maximum allocation rate

11JamaicaVM: Realt ime Response for Java Applications

Realtime Garbage Collection

Work based garbage collector

No GC thread

GC borrows application thread

Need only determine maximum memory use

No read barriers needed

Low latency

12JamaicaVM: Realt ime Response for Java Applications

Work-Based Garbage Collector

All Java Threads are realtime threads

GC work is performed at allocation time

GC work must be sufficient to recycle enough memory before free memory is exhausted

Execution time of all allocations must be bound

13JamaicaVM: Realt ime Response for Java Applications

JamaicaVM Builder Architecture

DefaultCode Generator

Machine Code Optimization

SSA Converter

Byte Code Reader

Java Byte Code

IntermediateCode

SSA Blocks

Machine Code

Object Code Writer

SSA IC Optimization

Machine Code Generator

Machine Code Generation Rules

SSA IC Optimization Rules

Object Code (ELF/PECOFF)

Machine Code Optimization Rules

Processor Definition

C Code Generator

C Compilation

C Code

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aicas Drives Standards Forward

Java Community Process

JSR 282: update Real-Time Specification for Java

JSR 302: Safety Critical Java

JSR 50: Distributed Realtime Java

SC-205/WG-71 Plenary

Update software standards for civil aviation:DO-178, -248, -278, -330, -331, -332, and -333

Active in SG-5: Object Oriented Technology

Java Modeling Language (JML)

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Major RTSJ Improvements

Raw Memory

Typed device access

Factory based

ActiveEvents

Unify API for Timer, Happening, & Signal

Happening object

ISR Support

Stateful Events & Handlers

Object & long

POSIX Realtime Signal

CPU Affinity

New Scope types

PinnableMemory

StackedMemory

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Applications

17JamaicaVM: Realt ime Response for Java Applications

JamaicaVM vs. Oracle’s JDK

JamaicaVM

Realtime GCno GC pauses

Supports realtime priorities w/ OS map

RTSJ APIsRealtimeThread,

AsyncEvent, etc.

Static compilation

Flexible license

Oracle’s JDK

Conventional GCGC causes pauses

Priorities ill defined w/o mapping to OS

No RTSJ support, just standard classes

JIT Only

One for all license(not free)

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Conclusion

State-of-the-art Java technology

Realtime garbage collection

Compilation and linking technology

Complete RTSJ implementation

multicore support

Market proven products

Dedicated to standards

Tools to ensure your system works correctly