IN4R21. Real-Time Specification for Java (RTSJ) Damien MASSON January 20, 2014

Transcription

1 IN4R21 Real-Time Specification for Java (RTSJ) Damien MASSON January 20, 2014

2 References Concurrent and Real-Time Programming in Java, Andy Wellings Real-Time Java Programming: With Java RTS, Eric J. Bruno et Greg Bollella 2/26

3 Thread Permits concurrent execution of several sequential codes to execute within the same process (so share memory) method main = new thread, 1 process: the VM the programmer can start new threads, modeled by the Thread class. Thread t = new Thread ( ) ; t. s t a r t ( ) ; execute method run() in a new Thread the method run() must be overridden Thread t = new Thread ( ) O v e r r i d e p u b l i c v o i d run ( ) { // h e l l o t. s t a r t ( ) ; 3/26

4 Runnable But direct redefinition of run() in Thread is a bad idea for a lot of good reasons: no multiple heritage with Java, field exists in Thread, the name space is not empty (e.g. Thread.name exists), no semantic separation between logic to execute and shell that model it for parallelism/concurrency. So there is the Runnable interface: Runnable l o g i c = new Runnable ( ) O v e r r i d e p u b l i c v o i d run ( ) { // h e l l o Thread t = new Thread ( l o g i c ) ; t. s t a r t ( ) ; Thread t2 = new Thread ( l o g i c ) ; t2. s t a r t ( ) ; 4/26

5 Priorities method setpriority(); 5/26

6 Threads Gesture suspend / stop() / destroy() / resume(): deprecated (must not be use) interrupt() yield() sleep() 6/26

7 Timer Permits to program executions 7/26

8 java.util.concurrent Contains a lot of tools to easily handle concurrency inherent issues, i.e without explicitly manipulate Thread: lesser chances to make mistakes. 8/26

9 Synchronisations permit to control/prevent the concurrent access to a piece of code (so to memory or other ressources) rendez-vous The more easy (but not recommanded!) p u b l i c c l a s s MyClass { p u b l i c s y n c h r o n i z e d v o i d mymethod ( ) { // code to p r o t e c t is equivalent to: p u b l i c v o i d mymethod ( ) { s y n c h r o n i z e d ( t h i s ) { // code to p r o t e c t (replace this by MyClass.getClass() for static methodes) 9/26

10 Synchronizations The good way: p u b l i c c l a s s MyClass { p r i v a t e f i n a l O b j e c t l o c k = new O b j e c t ( ) ; p u b l i c v o i d mymethod ( ) { s y n c h r o n i z e d ( l o c k ) { // code to p r o t e c t any Object can serve as lock the block structure prohibit to keep a lock beyond the method scope java 1.5 add the Lock object in order to address this limitation (does not concern this class) 10/26

11 Synchronizations This is not magic!! Warning: p u b l i c c l a s s MyClass { p r i v a t e f i n a l O b j e c t l o c k = new O b j e c t ( ) ; p u b l i c v o i d mymethod ( ) { // code p u b l i c v o i d myothermethod ( ) { s y n c h r o n i z e d ( l o c k ) { mymethod ( ) ; p u b l i c v o i d mysecondothermethod ( ) { mymethod ( ) ; Synchronized is only a wait to acquire a lock, it does permit to block an other piece of code to execute if this other piece of code does not ask the same lock. 11/26

12 rendez-vous Object.wait() Object.wait(timeout) Object.notify() Object.notifyAll(); 12/26

13 RTSJ philosophy No restriction to a specific version of Java RTSJ VM should be able to run any Java application Based on J2SE No syntax extension Does not require specific hardware Deterministic timing behavior 13/26

14 RTSJ Scope: Thread scheduling Memory Gesture Synchronization and resources sharing Asynchronous event handling Asynchronous transfer of control Timing and Clock System Functions 14/26

15 RTSJ one package: javax.realtime one spec for an rt-jvm one reference implementation: RI (tjvm) many other implementations: Java RTS, JamaïcaVM... 15/26

16 Scheduling (I) Runnable (I) Schedulable (C) Thread (C) AsyncEventHandler (C) RealtimeThread (C) BoundAsyncEventHandler (C) NoHeapRealtimeThread 16/26

17 Scheduling (C) Scheduler (C) PriorityScheduler (AC) SchedulingParameters (AC) ReleaseParameters (C) PriorityParameters (C) PeriodicParameters (C)... 16/26

18 Scheduling (C) Scheduler (I) Runnable (C) PriorityScheduler (I) Schedulable (C) Thread (AC) SchedulingParameters (AC) ReleaseParameters (C) AsyncEventHandler (C) RealtimeThread (C) PriorityParameters (C) PeriodicParameters (C)... (C) BoundAsyncEventHandler (C) NoHeapRealtimeThread 16/26

19 Simple Traffic Runnable l o g i c = new Runnable ( ) O v e r r i d e p u b l i c v o i d run ( ) { System. out. p r i n t l n ( "real - time hello " ) ; R e a l t i m e T h r e a d t = new R e a l t i m e T h r e a d ( l o g i c ) ; t. s t a r t ( ) ; Priority assignment with setschedulingparameters() (pretty much the same as setpriority(), but warning: the spec is the spec, implementations are implementations...), or directly to the constructor new R e a l t i m e T h r e a d ( new P r i o r i t y P a r a m e t e r s ( 1 5 ) ) ; Priority segementation between non RT (from 1 to 10) and RT (from 11 to at least 30) 17/26

20 Periodic traffic - RealtimeThread Runnable l o g i c = new Runnable ( ) O v e r r i d e p u b l i c v o i d run ( ) { do{ System. out. p r i n t l n ( " periodic hello in real - time " ) ; w h i l e ( w a i t F o r N e x t P e r i o d ( ) ) ; R e l a t i v e T i m e s t a r t = new R e l a t i v e T i m e ( ) ; R e l a t i v e T i m e p e r i o d = new R e l a t i v e T i m e ( , 0 ) ; P e r i o d i c P a r a m e t e r s param = new P e r i o d i c P a r a m e t e r s ( s t a r t, p e r i o d ) ; R e a l t i m e T h r e a d t = new R e a l t i m e T h r e a d ( param, l o g i c ) ; t. s t a r t ( ) ; waitfornextperiod returns false when the deadline is missed (implicit deadline is the default) 18/26

21 Absolute/Relative Time Date/duration: two subclasses of HighResolutionTime Permits to encode precise time (but does not mean this is the system granularity!!) Warning: most of these object s methods create objects p r i v a t e f i n a l AbsoluteTime abs = new AbsoluteTime ( ) ; p r i v a t e f i n a l R e l a t i v e T i m e r e l 1 = new R e l a t i v e T i m e ( ) ; p r i v a t e f i n a l R e l a t i v e T i m e r e l 2 = new R e l a t i v e T i m e ( ) ; v o i d mymethod ( ) { Clock. g e t R e a l t i m e C l o c k ( ). gettime ( abs ) ; r e l 1. s e t ( 1 0, 5 ) ; abs. s u b t r a c t ( r e l 1, r e l 2 ) ; p r i v a t e f i n a l R e l a t i v e T i m e r e l 1 = new R e l a t i v e T i m e ( ) ; p r i v a t e f i n a l R e l a t i v e T i m e r e l 2 = new R e l a t i v e T i m e ( ) ; v o i d methode ( ) { AbsoluteTime abs = Clock. g e t R e a l t i m e C l o c k ( ). gettime ( ) ; R e l a t i v e T i m e r e l 1 = new R e l a t i v e T i m e ( 1 0, 5 ) ; R e l a t i v e T i m e r e l 2 = abs. s u b t r a c t ( r e l 1 ) ; 19/26

22 Periodic Traffic - RealtimeThread Runnable l o g i c = new Runnable ( ) O v e r r i d e p u b l i c v o i d run ( ) { do{ System. out. p r i n t l n ( " periodic hello in real - time " ) ; w h i l e ( w a i t F o r N e x t P e r i o d ( ) ) ; R e l a t i v e T i m e s t a r t = new R e l a t i v e T i m e ( ) ; R e l a t i v e T i m e p e r i o d = new R e l a t i v e T i m e ( , 0 ) ; R e l a t i v e T i m e d e a d l i n e = new R e l a t i v e T i m e ( 5 0 0, 0 ) ; R e l a t i v e T i m e wcet = new R e l a t i v e T i m e ( 2 0 0, 0 ) ; P e r i o d i c P a r a m e t e r s param = new P e r i o d i c P a r a m e t e r s ( s t a r t, p e r i o d, wcet, d e a d l i n e, n u l l, n u l l ) ; R e a l t i m e T h r e a d t = new R e a l t i m e T h r e a d ( param, l o g i c ) ; t. s t a r t ( ) ; 20/26

23 Sporadic Traffic Runnable l o g i c = new Runnable ( ) O v e r r i d e p u b l i c v o i d run ( ) { System. out. p r i n t l n ( " Sporadic Hello " ) ; AsyncEventHandler h a n d l e r = new AsyncEventHandler ( l o g i c ) ; AsyncEvent e v e n t = new AsyncEvent ( ) ; e v e n t. addhandler ( h a n d l e r ) ; //... e v e n t. f i r e ( ) ; 21/26

24 Sporadic Traffic Runnable l o g i c = new Runnable ( ) O v e r r i d e p u b l i c v o i d run ( ) { System. out. p r i n t l n ( " Hey " ) ; AsyncEventHandler h a n d l e r = new AsyncEventHandler ( l o g i c ) ; AsyncEvent e v e n t = new AsyncEvent ( ) ; e v e n t. addhandler ( h a n d l e r ) ; AsyncEventHandler h a n d l e r 2 = new AsyncEventHandler ( l o g i c ) ; e v e n t. addhandler ( h a n d l e r 2 ) ; //... e v e n t. f i r e ( ) ; 22/26

25 Periodic Traffic - AE/AEH Runnable l o g i c = new Runnable ( ) O v e r r i d e p u b l i c v o i d run ( ) { System. out. p r i n t l n ( " Periodic Hello " ) ; AsyncEventHandler h a n d l e r = new AsyncEventHandler ( l o g i c ) ; R e l a t i v e T i m e s t a r t = new R e l a t i v e T i m e ( ) ; R e l a t i v e T i m e p e r i o d = new R e l a t i v e T i m e ( , 0 ) ; P e r i o d i c T i m e r t i m e r = new P e r i o d i c T i m e r ( s t a r t, p e r i o d, h a n d l e r ) ; AsyncEventHandler encapsulates Release/Scheduling Parameters, as RealtimeThread 23/26

26 Periodic Traffic - RealtimeThread Runnable l o g i c = new Runnable ( ) O v e r r i d e p u b l i c v o i d run ( ) { do{ System. out. p r i n t l n ( " periodic hello " ) ; w h i l e ( w a i t F o r N e x t P e r i o d ( ) ) ; R e l a t i v e T i m e s t a r t = new R e l a t i v e T i m e ( ) ; R e l a t i v e T i m e p e r i o d = new R e l a t i v e T i m e ( , 0 ) ; R e l a t i v e T i m e d e a d l i n e = new R e l a t i v e T i m e ( 5 0 0, 0 ) ; R e l a t i v e T i m e wcet = new R e l a t i v e T i m e ( 2 0 0, 0 ) ; AsyncEventHandler wcethand = new AsyncEventHandler ( /... / ) ; AsyncEventHandler deadhand = new AsyncEventHandler ( /... / ) ; P e r i o d i c P a r a m e t e r s param = new P e r i o d i c P a r a m e t e r s ( s t a r t, p e r i o d, wcet, d e a d l i n e, wcethand, deadhand ) ; R e a l t i m e T h r e a d t = new R e a l t i m e T h r e a d ( param, l o g i c ) ; t. s t a r t ( ) ; If the VM is able to detect faults, it call fire() method of encapsulated Event Beware of handlers priorities... 24/26

27 RTSJ : FA Delegated to the Scheduler addtofeasibility() isfeasible() bad idea! 25/26

28 Asynchronous transfer of control (interruption) Brings the possibility to stop an other thread Only if this thread executes a piece of code that has been explicitly marked as interruptable Use Exception AsynchronouslyInterruptedException Timed interruptible interrupt(); 26/26