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JTRES 2014
The Next Generation of the Real-Time Specifj fjcation for Java
- Dr. James J. Hunt
JSR 282 Spec Lead CEO aicas GmbH JTRES 2014
2 Real-TIme Specifj fjcation for Java 2.0
The Next Generation of the Real-Time Specifj fjcation for Java Dr. - - PowerPoint PPT Presentation
The Next Generation of the Real-Time Specifj fjcation for Java Dr. - - PowerPoint PPT Presentation
JTRES 2014 The Next Generation of the Real-Time Specifj fjcation for Java Dr. James J. Hunt JSR 282 Spec Lead CEO aicas GmbH JTRES 2014 What is the RTSJ? Support for realtime programming in Java importance vs fair scheduling determinism
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3 Real-TIme Specifj fjcation for Java 2.0
Constraints
No changes to the language
same bytecode no new language features
Fully compatible with convention Java implementations such as OpenJDK
Java programs should run correctly on RTSJ implementations that supports the required profjle Maximize code reuse under time complexity constraints
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4 Real-TIme Specifj fjcation for Java 2.0
Why Update the RTSJ?
Environment evolution
better realtime garbage collection Java 1.4 Java 1.8 →
Marketing
support different levels of realtime: even for conventional Java implementations reduce need for JNI deemphisize memory areas differencial to Android
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5 Real-TIme Specifj fjcation for Java 2.0
RTSJ 1.0.2 Issues
Device memory access ineffjcient
Single class for accessing all precision for each of integral and fmoating types:
RawMemoryAccess RawMemoryFloatAccess
Unclear how I/O memory is address: fjlters under defjned Access testing on every access Cannot type restrict memory access Hard to inline
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6 Real-TIme Specifj fjcation for Java 2.0
RTSJ 1.0.2 Issues
Happening ill defjned
No standard way to add new happenings Happenings not objects Inconsistent with other AsyncEvent types
POSIX Clock User triggered
Too many levels of indirection: Happening AsyncEvent AsyncEventHandler → → No support for fjrst level interrupt handlers
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7 Real-TIme Specifj fjcation for Java 2.0
RTSJ 1.0.2 Issues
No way to defjne a new Clock ScopedMemory
No simple way to use scopes for Producer- Consumer pattern No way to manage backing store
Multicore
no way to assign SOs to processors
Miscellaneous Defjciencies
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8 Real-TIme Specifj fjcation for Java 2.0
New Raw Memory Architecture
FactoryBased
RawMemory class for registration RawMemoryFactory for implementation
Interfaces for each access type: RawInt, RawShort, RawByte, RawFloat, etc. Concrete classes for
Memory mapped devices, I/O mapped devices, and Generic mapped devices.
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9 Real-TIme Specifj fjcation for Java 2.0
RawMemory Interfaces
javax.realtime::RawFloatWriter «interface» +setFloat(fmoat v) +setFloat(int ofgset, fmoat data) +set(int ofgset, fmoat[] v): int +set(int ofgset, fmoat[] v, int start, int count): int +address():long javax.realtime::RawFloat «interface» javax.realtime::RawFloatReader «interface» +getFloat():fmoat +getFloat(int ofgset):fmoat +get(int ofgset, fmoat[] v): int +get(int ofgset, fmoat[] v, int start, int count): int +address():long javax.realtime::RawDoubleWriter «interface» +setDouble(double v) +setDouble(int ofgset, double data) +set(int ofgset, double[] v): int +set(int ofgset, double[] v, int start, int count): int +address():long javax.realtime::RawDoubleReader «interface» +get():double +getDouble(int ofgset):double +get(int ofgset, double[] v): int +get(int ofgset, double[] v, int start, int count): int +address():long javax.realtime::RawDouble «interface» javax.realtime::RawByteWriter «interface» +setByte(byte v) +setByte(int ofgset, byte v) +set(int ofgset, byte[] v):int +set(int ofgset, byte[] v, int start, int count):int +address():long javax.realtime::RawByte «interface» javax.realtime::RawByteReader «interface» +getByte():byte +getByte(int ofgset):byte +get(int ofgset, byte[] v):int +get(int ofgset, byte[] v, int start, int count):int +address():long javax.realtime::RawShortWriter «interface» +setShort(short v) +setShort(int ofgset, short v) +set(int ofgset, short[] v):int +set(int ofgset, short[] v, int start, int count):int +address():long javax.realtime::RawShortReader «interface» +getShort():short +getShort(int ofgset):short +get(int ofgset, short[] v):int +get(int ofgset, short[] v, int start, int count):int +address():long javax.realtime::RawShort «interface» javax.realtime::RawIntWriter «interface» +setInt(int v) +setInt(int ofgset, int v) +set(int ofgset, int[] v):int +set(int ofgset, int[] v, int start, int count):int +address():long javax.realtime::RawIntReader «interface» +getInt():int +getInt(int ofgset):int +get(int ofgset, int[] v):int +get(int ofgset, int[] v, int start, int count):int +address():long javax.realtime::RawInt «interface» javax.realtime::RawLongWriter «interface» +setLong(long v) +setLong(int ofgset, long v) +set(int ofgset, long[] v):int +set(int ofgset, long[] v, int start, int count):int +address():long javax.realtime::RawLongReader «interface» +getLong():long +getLong(int ofgset):long +get(int ofgset, long[] v):int +get(int ofgset, long[] v, int start, int count):int +address():long javax.realtime::RawLong «interface» javax.realtime::RawMemory «interface» java.io::Closable «interface» +close() Visibility + = public # = protected ~ = package
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Example
Public class IOBusController implements RawShort { private MemoryRawByte command; private MemoryRawByte fmag; private MemoryRawShort address; private MemoryRawInt data; public int get(short address) { address.put(address); command.put(READ); while (fmag.get() != DONE); return data.get(); } ...
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DMA Support
Special factory for direct byte buffer
Get byte buffer that is visible DMA controller Means to get address to pass to DMA controller Could be use to implement I/O Channels
Additional barrier types
provide write visibility across JNI boundary for supporting DMA with direct byte buffers Coordinating with Doug Lea (JEP 188: Java Memory Model Update)
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Event Architecture
AbstractAsyncEvent AsyncEvent POSIXSignal
POSIXRealtimeSignal
ActiveEvent AsyncLongEvent AsyncObjectEvent Happening ISR Timer PeriodicTimer OneShotTimer
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Event Handler Architecture
AbstractAsyncEventHandler AsyncEventHandler
BoundAsyncLongEventHandler
AsyncLongEventHandler AsyncObjectEventHandler BoundAsyncEventHandler AbstractBound AsyncEventHandler
BoundObjectLongEventHandler
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Mix and Match
Types AsyncEvent AsyncLongEvent AsyncObjectEvent AsyncEventHandler No payload No payload No payload AsyncLongEventHandler Event ID Payload Event ID AsyncObjectEventHandler Event Object Event Object Payload
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Timer States
disabled disabled stopped active relative absolute absolute
- > FALSE
stop startDisabled stop
- > TRUE
- > TRUE
stop Any Call
- > IllegalStateException
nonexistant new Timer(AbsoluteTime, ..) destroy OneShotTimer fire active skip OneShotTimer fire and selfreschedule PeriodicTimer isRunning
- > TRUE
skip and selfreschedule PeriodicTimer isRunning
- > FALSE
isRunning
- > FALSE
- > IllegalStateException
getFireTime new Timer(RelativeTime, ..) RelativeTime reschedule reschedule RelativeTime reschedule reschedule AbsoluteTime AbsoluteTime
- > IllegalStateException
startDisabled IllegalStateException start getFireTime
- > absoluteTime
- > start +
relativeTime getFireTime start enable disable absolute enabled active relative disabled active enabled disabled relative stopped destroyed
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AbstractAsyncEvent States
new AbstractAsyncEvent(..)
isRunning isRunning
- > FALSE
- > TRUE
enable disable
enabled disabled nonexistant
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Happening: Kind of AsyncEvent
AsyncEvent
Passive (fjre mechanism) Runs all associated event handlers User defjnable
Happenings
supports active behavior too (trigger mechanism) Can have (needs) dispatcher to manage activity Can be triggered from outside the VM
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Happening Sequence
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User Defj fjned Clocks
Like an ISR
no active thread just triggers associated Timers
Manages Trigger Queue
next set of Timers (in priority order) to trigger time ordered set of Timer sets constant trigger time for top next Timer bound adding and deleting
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20 Real-TIme Specifj fjcation for Java 2.0
Clock Sequence Diagram
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21 Real-TIme Specifj fjcation for Java 2.0
Sleep with Application Clock
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22 Real-TIme Specifj fjcation for Java 2.0
Affj fjnity
Multicore control
enable pinning Threads and AsyncEventHandlers to a subset of processors. support collective pinning w/ ProcessingGroupParameters fjnd out what processors and processor subsets are available for pinning pinning to single processors is always supported.
- rthogonal to all other RTSJ classes
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Entering MemoryAreas
Provide for passing arguments
use lamda and closure can be optimized to prevent allocation
Provide a return value
Use Supplier API adds many methods
fjve types: Object<T>, int, long, double, and boolean enter, executeInArea, joinAndEnter, and joinAndEnter with timeout 10–20 new methods!
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New ScopedMemory Areas
PinnedMemory
subclass of ScopedMemory similar to LT Memory except supports pinning
StackedMemory
subclass of ScopedMemory (supports SCJ Model) similar to LT Memory but reserves backing store backing store from parent when StackedMemory enterable only from MemoryArea where created resize to max reserved (when no sub area)
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StackedMemory Example
Nesting 0 Nesting 0 Split A Nesting 2 Nesting 1 Split B Nesting 1 Split A Nesting 1 Nesting 2 Split C Nesting 3
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Small Change
RealtimeThread
add waitForNextRelease() and release() for aperiodic processing
AsyncEventHandler
memory area entered on each release
- ld behavior obtained by using PinnableMemory
ReleaseParameters
add blocking factor to support feasibility analysis
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Small Change
PreallocatedThrowable
ThrowBoundryException OutOfMemoryException
Phasing control for periodic schedulables
when start() called after absolute start time now, phased, all past, & exception
PhysicalMemory
Update documentation to improve clarity. Separate from RawMemory
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Small Change
RelativeTime
add compareTo0() add scale(int factor)
Timed
add reset() method better support for watchdog timers
PriorityCeilingEmulation
now required in base module
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Small Change
Consistency
provide for fjring an AsyncEvent (or release an AsyncEventHandler) on all resource limit errors. new methods as necessary to provide both a returned object and one that takes a destination, e.g., to reuse HighResolutionTime objects update semantics for cost enforcement to permit a schedulable's CPU use to be bound by its cost parameter in each period soft cost enforcement
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Modularization Goals
Provide useful subsets of the RTSJ
with and without a realtime GC with and without device support
Encourage more implementations
Hard realtime, e.g., for control systems Soft realtime, e.g. for system monitoring No realtime, e.g., for development
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Modules
Base
Schedulables Priority Inheritance Clock ...
Device
Happenings RawMemory ...
Memory Area
immortal physical scoped
Advanced Options
ATC ISR
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Conclusion
A common API for realtime Java
provides for realtime sceduling and control support interaction with environment reduce need for external code
Base for a dynamic cyberphysical platform
robust basis resource control recognizes realtime requirement
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33 aicas GmbH
Contact Information
- Dr. James J. Hunt