Oplægget blev holdt ved et seminar i InfinIT-interessegruppen Højniveau sprog til indlejrede systemer den 19. august 2009. Læs mere om interessegruppen på http://www.infinit.dk/dk/interessegrupper/hoejniveau_sprog_til_indlejrede_systemer/

1. Predictable Java
• Overview
• Implementations
• Next steps
Infinit Højniveausprog, 19 August 2009
Anders P. Ravn and Hans Søndergaard
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2. A Real-Time Application
• Periodic Event Handlers
• Aperiodic Event Handlers
collected in a mission
• Mission Handler
Each handler
has a Memory
is Scheduled
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3. Periodic handler
class Periodic extends PeriodicEventHandler
{
protected Periodic(.., PeriodicParameters pp,
Scheduler scheduler,
MemoryArea memory);
public void handleEvent() {
// the logic to be executed every period
}
}
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4. Aperiodic handler
class Aperiodic extends AperiodicEventHandler
{
protected Aperiodic(.., AperiodicParameters ap,
Scheduler scheduler,
MemoryArea memory);
public void handleEvent() {
// the logic to be executed when an event occurs
}
}
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5. A simple mission
public class Basic extends Mission
{
protected Basic(.., AperiodicParameters ap,
Scheduler scheduler,
MemoryArea memoryArea)
{
... // initialization
}
public static void main (String[] args) {
new Basic( null, null,
new CyclicScheduler(),
new LTMemory(10*1024));
}
}
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6. …The mission
addToMission(
new Periodic( null, pp, getScheduler(),
new LTMemory(1024)));
addToMission(
new Periodic( null, pp, getScheduler(),
new LTMemory(1024)));
...
add(); // mission to its scheduler
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7. Complex mission
private Mission[] mission;
private int active = 0;
static AperiodicEvent event;
public ThreeSequentialMissions(...) {
mission = new Mission[3];
// set up the three missions
mission[0] = new Mission(...);
// add handlers for mission 0
// including the mission termination
...
mission[1] = new Mission();
...
// start the first mission
mission[active].add();
event = new AperiodicEvent(this);
}
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8. Changing mission
private Mission[] mission;
private int active = 0;
static AperiodicEvent event;
public ThreeSequentialMissions(...) {
...
}
public void handleEvent() {
mission[active].remove();
active = (active + 1) % mission.length;
mission[active].add();
}
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9. Level 0
• only Periodic Event Handlers
• cyclic scheduler
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10. Level 1
SO 3 has the
highest priority
• periodic and aperiodic event handlers
• fixed-priority preemptive scheduler
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11. Implementations
• On top of RTSJ (adapter)
• Native implementation using
– JamVM
– Xenomai/Linux
– Mechatronic Brick
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12. Schedulers
• Cyclic scheduler
– Only one mission, with periodic handlers
– Using cyclic executive model
– The Scheduler: a periodic RT_TASK
• period = gcd of all the handler periods
• Fixed priority pre-emptive scheduler
– Missions with periodic and aperiodic handlers
– Implemented as RT_TASKs
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13. Memory
• No GC
• Two types of memory
– Immortal memory = Heap (without GC)
• Lifetime = lifetime of the application
– Scoped memory
• Each handler has its own private memory
• Lifetime = lifetime of the handler
• Object allocation rewritten in JamVM
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14. Synchronization
• Java’s locking model (synchronization)
– does not fit to avoid priority inversion
• Xenomai's MUTEX enforce priority inheritance
• Rewritten JamVM
– synchronized methods in classes for shared objects:
• uses MUTEX lock/unlock
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15. Next steps: Workbench
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16. Next steps
• Eclipse plugins
• Homepage for Predictable Java
• Different tools for static analyses
• Examples
• ...
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17. References
• A predictable Java profile - rationale and implementations
Thomas Bøgholm, René R. Hansen, Anders P. Ravn, Bent Thomsen,
and Hans Søndergaard
JTRES’09. 23-25 September 2009.
• Safety-Critical Java
JSR 302: Safety Critical Java Technology
http://jcp.org/en/jsr/detail?id=302
• Java for Safety-Critical Applications
Thomas Henties, James J. Hunt, Doug Locke, Kelvin Nilsen, Martin
Schoeberl, Jan Vitek.
SafeSert 2009.
• Safety Critical Specification for Java
Version 0.5. August 2008. Draft.
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