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package examples.pilib
import scala.concurrent.pilib._
object scheduler {
/**
* Random number generator.
*/
val random = new util.Random()
//***************** Scheduler ******************//
/**
* A cell of the scheduler whose attached agent is allowed to start.
*/
def A(a: Chan[Unit], b: Chan[Unit])(d: Chan[Unit], c: Chan[Unit]) {
///- ... complete here ...
choice ( a * { x => C(a, b)(d, c) })
///+
}
/**
* A cell of the scheduler in another intermediate state.
*/
def C(a: Chan[Unit], b: Chan[Unit])(d: Chan[Unit], c: Chan[Unit]) {
///- ... complete here ...
choice (c * { x => B(a, b)(d, c) })
///+
}
/**
* A cell of the scheduler whose attached agent is allowed to finish.
*/
def B(a: Chan[Unit], b: Chan[Unit])(d: Chan[Unit], c: Chan[Unit]) {
///- ... complete here ...
// choice (b * { x => D(a, b)(d, c) }) // incorrect naive solution
choice (
b * { x => choice ( d(()) * A(a, b)(d, c) ) }, // b.'d.A
d(()) * (choice (b * { x => A(a, b)(d, c) })) // 'd.b.A
)
///+
}
/**
* A cell of the scheduler whose attached agent is not yet allowed to start.
*/
def D(a: Chan[Unit], b: Chan[Unit])(d: Chan[Unit], c: Chan[Unit]) {
///- ... complete here ...
choice (d(()) * A(a, b)(d, c))
///+
}
//***************** Agents ******************//
def agent(i: Int)(a: Chan[Unit], b: Chan[Unit]) {
// 50% chance that we sleep forever
if (i == 0 && random.nextInt(10) < 5) {
a.attach(x => println("Start and sleeps ----> " + i))
Thread.sleep(random.nextInt(1000))
a.write(())
}
else {
a.attach(x => println("Start ----> " + i))
b.attach(x => println("Stop -> " + i))
Thread.sleep(random.nextInt(1000))
a.write(())
Thread.sleep(random.nextInt(1000))
b.write(())
agent(i)(a, b)
}
}
//***************** Entry function ******************//
/**
* Creates a scheduler for five agents (programs).
*/
def main(args: Array[String]) {
val agentNb = 5
val agents = List.range(0, agentNb) map agent
scheduleAgents(agents)
}
//***************** Infrastructure *****************//
/**
* A cell is modelled as a function that takes as parameters
* input and output channels and which returns nothing.
*/
type Cell = (Chan[Unit], Chan[Unit]) => Unit
/**
* Creates a cell composed of two cells linked together.
*/
def join(cell1: Cell, cell2: Cell): Cell =
(l: Chan[Unit], r: Chan[Unit]) => {
val link = new Chan[Unit];
spawn < cell1(l, link) | cell2(link, r) >
};
/**
* Links the output of a cell to its input.
*/
def close(cell: Cell) {
val a = new Chan[Unit]
cell(a, a)
}
/**
* Creates a cell consisting of a chain of cells.
*/
def chain(cells: List[Cell]): Cell =
cells reduceLeft join
/**
* Creates a cell consisting of a chain of cells.
*/
def makeRing(cells: List[Cell]): Unit =
close(chain(cells))
/**
* An agent is modelled as a function that takes as parameters channels to
* signal that it has started or finished.
*/
type Agent = (Chan[Unit], Chan[Unit]) => Unit
/**
* Takes a list of agents and schedules them.
*/
def scheduleAgents(agents: List[Agent]) {
var firstAgent = true;
val cells = agents map (ag => {
val a = new Chan[Unit];
val b = new Chan[Unit];
spawn < ag(a, b) >;
(d: Chan[Unit], c: Chan[Unit]) => if (firstAgent) {
firstAgent = false;
A(a, b)(d, c)
}
else
D(a, b)(d, c)
});
makeRing(cells)
}
}
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