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--- sleeping-barber [2007/10/23 21:30] – created franck
+++ sleeping-barber [2007/10/29 20:51] (current) – cs253184
@@ Line 8: / Line 8: @@
 sit down (if there are empty chairs) or leave the shop (if all
 chairs are full).  The problem is how to program the barber
-and the customers without getting into race conditions.
+and the customers without getting into race conditions.                                                 In your solution, you may want to introduce a class ''Shop''. The ''Shop'' object has-a ''Barber'' object.  A ''Barber''
-In your solution, you may want to introduce a class ''Shop''.
-A ''Shop'' object has-a ''Barber'' object.  A ''Barber''
 object is-a ''Thread'' object.  The ''run'' method of the
 ''Barber'' class should give rise to the output
@@ Line 25: / Line 22: @@
 ''Customer i leaves''.
+An applet of this problem can be found
+[[http://colos1.fri.uni-lj.si/%7Ecolos/Colos/EXAMPLES/MARIBOR/barber|here]].
+<code java>
+public class Barber extends Thread
+{
+  public void run()
+  {
+    while (true)
+    {
+      while (shop.isEmpty())
+      {
+        try
+        {
+          this.wait();
+        }
+        catch (InterruptedException e) {}
+      }
+    }
+  }
+}
+</code>
+<code java>
+public class Customer extends Thread
+{
+  private int id;
+  private Shop shop;
+  public Customer(int id)
+  {
+    super();
+    this.id = id;
+  }
+  public void run()
+  {
+    while (true)
+    {
+      System.out.println("Customer " + this.id + " enters");
+      int number = shop.getChair();
+      if (number != -1)
+      {
+        System.out.println("Customer " + this.id + " sits down");
+        while (!shop.isFirst(number))
+        {
+          try
+          {
+            this.wait();
+          }
+          catch (InterruptedException e) {}
+        }
+        System.out.println("Customer " + this.id + " gets a haircut");
+        while (!shop.isDone())
+        {
+          try
+          {
+            this.wait();
+          }
+          catch (InterruptedException e) {}
+        }
+      }
+      System.out.println("Customer " + this.id + " leaves");
+    }
+  }
+}
+</code>
+<code java>
+public class Shop
+{
+  private Barber barber;
+  public final int NUMBER_OF_CHAIRS = 8;
+  private int first;
+  private int next;
+  private boolean done;
+  public synchronized int getChair()
+  {
+    if (this.next - this.first > Shop.NUMBER_OF_CHAIRS)
+    {
+      return -1;
+    }
+    else
+    {
+      this.notifyAll();
+      return last++;
+    }
+  }
+  public synchronized boolean isFirst(int number)
+  {
+    return this.first == number;
+  }
+  public synchronized boolean isDone()
+  {
+    return this.done;
+  }
+}
+</code>
+Another sketch of a solution can be found
+[[http://www.cse.yorku.ca/~franck/teaching/2002-03/6490A/0502.html|here]].
+Slawomir's running (!!!) solution can be found [[discussion|here]].