Concurrency 3 Concurrent Execution Alexandre David - - PowerPoint PPT Presentation
Concurrency 3 Concurrent Execution Alexandre David adavid@cs.aau.dk Credits for the slides: Claus Brabrand Jeff Magee & Jeff Kramer 1 Repetition Concepts: We adopt a model-based approach for the design and construction of
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adavid@cs.aau.dk Credits for the slides: Claus Brabrand Jeff Magee & Jeff Kramer
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➢ Concepts: We adopt a model-based approach
➢ Models: We use finite state models to
➢ Practice: We use Java for constructing
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➢ Based on Labelled Transition Systems (LTS) ➢ Described textually as Finite State Processes
speed engineOn engineOff
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➢ Finite State Processes (FSP):
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➢ Subclassing java.lang.Thread: ➢ Implementing java.lang.Runnable:
class MyThread extends Thread { public void run() { // ... } } class MyRun implements Runnable { public void run() { // ... } } Thread t = new MyThread(); t.start(); // ... Thread t = new Thread(new MyRun()); t.start(); // ...
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➔ Parallelism (aka. “Real” Concurrent Execution)
Time
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Time
➔ Concurrency (aka. Pseudo-Concurrent Execution)
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Time
Time
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➢ How do we model concurrency? ➢ Arbitrary relative order of actions from
x
y
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➢ How should we model process execution speed? ➢ We abstract away time: arbitrary speed! a b x y
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2 states 3 states (0,0) (0,1) (0,2) (1,2) (1,1) (1,0)
2 x 3 states
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3 states 3 states 3 x 3 states?
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3 states 3 states 3 x 3 states?
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3 states 3 states
4 states!
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r e a d y use
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r e a d y use
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a:USER a.acquire a.use
a.release
b:USER
b.acquire b.use b.release
b.acquire a.acquire b.release a.release
{a,b}::RESOURCE
b.acquire b.use b.release
a.use a.acquire a.release RESOURCE_SHARE
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call wait reply continue
request call service reply
call service reply
continue
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acquire tau release
USER
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acquire tau release
USER
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acquire tau release
USER
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acquire tau release
USER
acquire release
USER
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T
a b
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T
a b
P
a b
Q
m
c d c x x x
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T
a b
P
a b
Q
m
A B
a c d c x x x
S
y x
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a:BUFF b:BUFF
a.out
TWOBUFF
in in
in
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CLIENTv2
call accept
SERVERv2
call service continue
CLIENT
call request
SERVER
call reply wait reply service continue
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printer
b:USER
printer
printer: RESOURCE
acquire release
RESOURCE = (acquire->release->RESOURCE). USER = (printer.acquire->use->printer.release->USER). ||PRINTER_SHARE = (a:USER || b:USER || {a,b}::printer:RESOURCE).
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THREAD = OFF, OFF = (toggle->ON |abort->STOP), ON = (toggle->OFF |output->ON |abort->STOP). ||THREAD_DEMO = (a:THREAD || b:THREAD) /{stop/{a,b}.abort}. Interpret:
as inputs
as output a:T b:T
stop a.toggle a.output b.output b.toggle
THREAD_DEMO
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class MyThread extends Thread { private boolean on; MyThread() {
} void toggle() { on = !on; } void abort() { interrupt(); } private void output() { System.out.println(“output”); } public void run() { try { while (true) { if (on) output(); sleep(1000); } } catch(InterruptedException _) { System.out.println(“Done!”); } } }
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class MyThread extends Thread { private boolean on; MyThread() {
} void toggle() { on = !on; } void abort() { interrupt(); } private void output() { System.out.println(“output”); } public void run() { try { while (true) { if (on) output(); sleep(1000); } } catch(InterruptedException _) { System.out.println(“Done!”); } } }
Interpret:
as inputs
as output
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class ThreadDemo { private stop(MyThread a, MyThread b) { a.abort(); b.abort(); } public static void main(String[] args) { MyThread a = new MyThread(); MyThread b = new MyThread(); a.start(); b.start(); while (true) { switch (readChar()) { case ‘a’: a.toogle(); break; case ‘b’: b.toogle(); break; case ‘i’: stop(a,b); return; } } } }
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➢ Concepts: concurrent processes and process
➢ Models:
– asynchronous (arbitrary speed) & interleaving (arbitrary
– parallel composition (finite state process with action
– process interaction (shared actions) – process labeling, action relabeling, and hiding – structure diagrams
➢ Practice: multiple threads in Java.