7. The concurrent extension JavaT of Javaε

ps lab 김윤경

content

7.1 Static semantics of JavaT

7.2 Transition rules for JavaT

7.2.1 Scheduling of multiple threads7.2.2 Thread methods

7.3 Thread invariants Example7.3.1

7.1 Static semantics of JavaT

7.1.1 Vocabulary of JavaT

cont : Thread -> (Frame*, Frame)

Fig. 7.1 Syntax of JavaT

Stm := …| synchronized( Exp ) Stm

must be a reference type

monitors : a mechanism for allowing only one thread at a time to execute a region of code protected by the monitor.

locks : When a synchronized statement is processed, the executing thread must grab the lock which is associated with the target reference .

sync: Thread ->Ref*locks : Ref ->NatwaitSet : Ref -> Powerset(Thread)exec : Thread -> ThreadStatedata ThreadState = NotStarted | Active | Synchronizing |

Waiting | Notified | DeadsyncObj : Thread -> RefwaitObj : Thread -> RefInterruptedFlag : Thread -> Bool

7.2 Transition rules for JavaT

7.2.1 Scheduling of multiple threads

execJavaThread= choose q∈dom(exec), runnable(q) if q=thread ∧exec(q) =Active then execJava else if exec(thread)=Active then cont(thread):=(frames,(meth, restbody, pos,locals)) thread :=q

run(q)

runnable(q)= case exec(q) of Active ->True

Synchronizing ->locks(syncObj(q))=0 Notified->locks(waitObj(q))=0

run(q) =switchCont(q)if exec(q) =Synchronizing then

synchronize(q)if exec(q)=Notified then

wakeup(q)

switchCont(q)=let (frames’,(meth’,restbody’,pos’,locals’)) = cont(q)

exec(q):=Active meth:=meth’ restbody:=restbody’ pos:=pos’ locals:=locals’ frames:=frames’

synchronize(q)=sync(q):=[syncObj(q)]·sync(q)locks(syncObj(q)):=1

wakeup(q)=locks(waitObj(q)):=occurrences(waitObj(q),sync(q))

7.2.2 Thread methods

start(ref ) = if exec(ref ) = NotStarted then fail (IllegalThreadStateException) else let q = getField(ref , Thread/ "target" ) meth = lookup(classOf (q),Thread/run())/run() exec(ref ) := Active cont(ref ) := ([ ], (meth, body(meth), firstPos,{( "this”, q)})) yieldUp(Norm)

interrupt(q) = yieldUp(Norm) if exec(q) = Waiting ∧ ￢ classInitialization(q) then let (frames’, (meth’, restbody’, pos’, locals’)) = cont(q) let fail = restbody’[throw new InterruptedException(); /pos’] let ref = waitObj (q) waitSet(ref ) := waitSet(ref ) ＼ {q}

exec(q) := Notified cont(q) := (frames’, (meth’, fail , pos’, locals’)) interruptedFlag(q) := False else interruptedFlag(q) := True classInitialization(q) = q ∈ ran(initThread) ∨ q ∈ ∪ ran(initWait)

wait(ref ) = if ref ∈ sync(thread) then fail (IllegalMonitorStateException) else let ret = restbody[Norm/up(pos)] waitSet(ref ) := waitSet(ref ) ∪{thread} locks(ref ) := 0 exec(thread) := Waiting waitObj (thread) := ref

cont(thread) := (frames; (meth; ret; up(pos); locals)) yieldUp(Norm)

notify(ref ) =if ref ∈ sync(thread) then

fail (IllegalMonitorStateException)else

yieldUp(Norm)choose q ∈ waitSet(ref )waitSet(ref ) := waitSet(ref ) ＼ {q}exec(q) := Notified

notifyAll (ref ) = if ref ∈sync(thread) then

fail (IllegalMonitorStateException)else

waitSet(ref ) := 0 yieldUp(Norm)forall q ∈ waitSet(ref )

exec(q) := Notified

7.3 Thread invariantsTheorem 7.3.1(thread) classOf (thread)≤h Thread.(exec1) dom(exec) is exactly the set of all threads.(exec2) If exec(q) =NotStarted, then sync(q) = [ ].(sync1) If ref ∈ sync(q), then ref ∈ dom(heap).(sync2) If synchronizing(q, ref ), then ref ∈ dom(heap), ref ∈ sync(q) and[ref ] sync(q) = syncFromCont(q).(sync3) If exec(q) ∈{Synchronizing, NotStarted}, thensync(q) = syncFromCont(q).(wait1) If waiting(q, ref ), then q ∈ waitSet(ref ) and ref ∈ sync(q).(wait2) If q ∈ waitSet(ref ), then q is a thread and waiting(q, ref ).(notied) If notified(q, ref ), then q ∈ waitSet(ref ) and ref ∈ sync(q).(dead) If exec(q) = Dead, then the frame stack of q is empty, waitSet(q) = 0 and sync

(q) = [ ].(lock1) If locked(q, ref ), then locks(ref ) = occurrences(ref, sync(q)).(lock2) If locked(q1, ref ) and locked(q2, ref ), then q1 = q2.(lock3) If locks(ref) > 0, then locked(ref ).

Example7.3.1

1. he appends a piece of text to the book;2. he notifies another author (or the publisher);3. he releases the lock of the book;4. he waits until he gets notified himself.

If the book is finished, he notifies another author (or the publisher) and terminates his work.

The publisher waits until the book is finished. He then prints the

book and notifies all waiting authors.