Java/Threads/Semaphore

An implementation of a producer and consumer that use semaphores to control synchronization.

   <source lang="java">
  
  

import java.util.concurrent.Semaphore; class Queue {

 int value;
 static Semaphore semCon = new Semaphore(0);
 static Semaphore semProd = new Semaphore(1);
 void get() {
   try {
     semCon.acquire();
   } catch (InterruptedException e) {
     System.out.println("InterruptedException caught");
   }
   System.out.println("Got: " + value);
   semProd.release();
 }
 void put(int n) {
   try {
     semProd.acquire();
   } catch (InterruptedException e) {
     System.out.println("InterruptedException caught");
   }
   this.value = n;
   System.out.println("Put: " + n);
   semCon.release();
 }

} class Producer implements Runnable {

 Queue q;
 Producer(Queue q) {
   this.q = q;
   new Thread(this, "Producer").start();
 }
 public void run() {
   for (int i = 0; i < 20; i++)
     q.put(i);
 }

} class Consumer implements Runnable {

 Queue q;
 Consumer(Queue q) {
   this.q = q;
   new Thread(this, "Consumer").start();
 }
 public void run() {
   for (int i = 0; i < 20; i++)
     q.get();
 }

} public class ProdCon {

 public static void main(String args[]) {
   Queue q = new Queue();
   new Consumer(q);
   new Producer(q);
 }

}

 </source>
   
  
 
  

A semaphore

   <source lang="java">
 

import java.util.concurrent.Semaphore; public class Main {

 public static void main(String args[]) throws Exception {
   Semaphore sem = new Semaphore(1, true);
   Thread thrdA = new Thread(new SyncOutput(sem, "Message 1"));
   Thread thrdB = new Thread(new SyncOutput(sem, "Message 2!"));
   thrdA.start();
   thrdB.start();
   thrdA.join();
   thrdB.join();
 }

} class SyncOutput implements Runnable {

 Semaphore sem;
 String msg;
 SyncOutput(Semaphore s, String m) {
   sem = s;
   msg = m;
 }
 public void run() {
   try {
     sem.acquire();
     System.out.println(msg);
     Thread.sleep(10);
   } catch (Exception exc) {
     System.out.println("Error Writing File");
   }
   sem.release();
 }

}

 </source>
   
  
 
  

Semaphore that can allow a specified number of threads to enter, blocking the others.

   <source lang="java">

/*

* JBoss, Home of Professional Open Source
* Copyright 2005, JBoss Inc., and individual contributors as indicated
* by the @authors tag. See the copyright.txt in the distribution for a
* full listing of individual contributors.
*
* This is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/

import java.io.PrintWriter; import java.io.StringWriter; import java.util.HashMap; import java.util.Iterator; import java.util.LinkedList; import java.util.Map; /**

* Semaphore that can allow a specified number of threads to enter, blocking the
* others. If the specified number of threads is 1, it acts as an exclusive
* semaphore and can be used instead of synchronized blocks
* 
* @author 
* @version $Revision: 2787 $
*/

interface Sync {

 /**
  * Acquires this sync
  * 
  * @see #release
  * @throws InterruptedException
  */
 void acquire() throws InterruptedException;
 /**
  * Releases this sync
  * 
  * @see #acquire
  */
 void release();

}

 </source>
   
  
 
  

Wait exclusive semaphore with wait - notify primitives

   <source lang="java">

/*

* JBoss, Home of Professional Open Source
* Copyright 2005, JBoss Inc., and individual contributors as indicated
* by the @authors tag. See the copyright.txt in the distribution for a
* full listing of individual contributors.
*
* This is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/

import java.io.PrintWriter; import java.io.StringWriter; import java.util.HashMap; import java.util.Iterator; import java.util.LinkedList; import java.util.Map; /*

* JBoss, Home of Professional Open Source Copyright 2005, JBoss Inc., and
* individual contributors as indicated by the @authors tag. See the
* copyright.txt in the distribution for a full listing of individual
* contributors.
* 
* This is free software; you can redistribute it and/or modify it under the
* terms of the GNU Lesser General Public License as published by the Free
* Software Foundation; either version 2.1 of the License, or (at your option)
* any later version.
* 
* This software is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
* FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
* details.
* 
* You should have received a copy of the GNU Lesser General Public License
* along with this software; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA, or see the FSF
* site: http://www.fsf.org.
*/

/**

* Wait exclusive semaphore with wait - notify primitives
* 
* @author 
* @version $Revision: 2787 $
*/

interface WaitSync extends Sync {

 /**
  * Pone in wait status this sync, until {@link #doNotify} is called to wake it
  * up.
  * 
  * @see #doNotify
  * @throws InterruptedException
  */
 void doWait() throws InterruptedException;
 /**
  * Wakes up this sync that has been posed in wait status by a {@link #doWait}
  * call. If this sync is not waiting, invoking this method should have no
  * effect.
  * 
  * @see #doWait
  * @throws InterruptedException
  */
 void doNotify() throws InterruptedException;

}

 </source>