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package examples.pilib
/** Solution of exercise session 6 (first question). */
object semaphore {
import scala.concurrent.pilib._
class Signal extends Chan[unit] {
def send = write(())
def receive = read
}
/** Interface. */
trait Semaphore {
def get: unit
def release: unit
}
/** First implementation. */
class Sem1 extends Semaphore {
private val g = new Signal
private val r = new Signal
def get: unit = g.send
def release: unit = r.send
private def Sched: unit = choice (
g * (x => { r.receive; Sched }),
r * (x => Sched)
)
spawn< Sched >
}
/** Second implementation. */
class Sem2 extends Semaphore {
private val a = new Signal
private val na = new Signal
def get: unit = { a.receive; spawn< na.send > }
def release: unit = choice (
a * (x => spawn< a.send >),
na * (x => spawn< a.send >)
)
spawn< a.send >
}
/** Test program. */
def main(args: Array[String]): unit = {
val random = new java.util.Random()
val sem = new Sem2
def mutex(p: => unit): unit = { sem.get; p; sem.release }
spawn< {
Thread.sleep(1 + random.nextInt(100));
mutex( {
System.out.println("a1");
Thread.sleep(1 + random.nextInt(100));
System.out.println("a2")
} )
} | {
Thread.sleep(1 + random.nextInt(100));
mutex( {
System.out.println("b1");
Thread.sleep(1 + random.nextInt(100));
System.out.println("b2")
} )
} >;
}
}
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