Data commit

Task/Mutex/Java/mutex-1.java

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+import java.util.concurrent.Semaphore;
+
+public class VolatileClass{
+   public Semaphore mutex = new Semaphore(1); //also a "fair" boolean may be passed which,
+                                              //when true, queues requests for the lock
+   public void needsToBeSynched(){
+      //...
+   }
+   //delegate methods could be added for acquiring and releasing the mutex
+}

Task/Mutex/Java/mutex-2.java

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+public class TestVolitileClass throws Exception{
+   public static void main(String[] args){
+      VolatileClass vc = new VolatileClass();
+      vc.mutex.acquire(); //will wait automatically if another class has the mutex
+                          //can be interrupted similarly to a Thread
+                          //use acquireUninterruptibly() to avoid that
+      vc.needsToBeSynched();
+      vc.mutex.release();
+   }
+}

Task/Mutex/Java/mutex-3.java

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+public class Main {
+    static Object mutex = new Object();
+    static int i = 0;
+
+    public void addAndPrint()
+    {
+        System.out.print("" + i + " + 1 = ");
+        i++;
+        System.out.println("" + i);
+    }
+
+    public void subAndPrint()
+    {
+        System.out.print("" + i + " - 1 = ");
+        i--;
+        System.out.println("" + i);
+    }
+
+
+    public static void main(String[] args){
+        final Main m = new Main();
+        new Thread() {
+            public void run()
+            {
+                while (true) { synchronized(m.mutex) { m.addAndPrint(); } }
+            }
+        }.start();
+        new Thread() {
+            public void run()
+            {
+                while (true) { synchronized(m.mutex) { m.subAndPrint(); } }
+            }
+        }.start();
+    }
+}