From 53a3cc7b17f4cf97075b7e71720777fd84109696 Mon Sep 17 00:00:00 2001
From: Gilles Dubochet <gilles.dubochet@epfl.ch>
Date: Fri, 16 Dec 2005 18:44:33 +0000
Subject: Created proper 'docs' folder for new layout.

---
 docs/examples/pilib/semaphore.scala | 72 +++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)
 create mode 100644 docs/examples/pilib/semaphore.scala

(limited to 'docs/examples/pilib/semaphore.scala')

diff --git a/docs/examples/pilib/semaphore.scala b/docs/examples/pilib/semaphore.scala
new file mode 100644
index 0000000000..cfb0c8e5a2
--- /dev/null
+++ b/docs/examples/pilib/semaphore.scala
@@ -0,0 +1,72 @@
+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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