Java by API/java.util.concurrent.locks/ReentrantLock

new ReentrantLock()

  
/*
License for Java 1.5 "Tiger": A Developer"s Notebook
     (O"Reilly) example package
Java 1.5 "Tiger": A Developer"s Notebook (O"Reilly) 
by Brett McLaughlin and David Flanagan.
ISBN: 0-596-00738-8
You can use the examples and the source code any way you want, but
please include a reference to where it comes from if you use it in
your own products or services. Also note that this software is
provided by the author "as is", with no expressed or implied warranties. 
In no event shall the author be liable for any direct or indirect
damages arising in any way out of the use of this software.
*/

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
 class LinkList<E> {
  // The value of this node
  E value;
  // The rest of the list
  LinkList<E> rest;
 
  // A lock for this node
  Lock lock;
  // Signals when the value of this node changes
  Condition valueChanged;
  // Signals when the node this is connected to changes
  Condition linkChanged;
  public LinkList(E value) {
    this.value = value;
    rest = null;
    lock = new ReentrantLock();
    valueChanged = lock.newCondition();
    linkChanged = lock.newCondition();
  }
  public void setValue(E value) {
    lock.lock();
    try {
      this.value = value;
      // Let waiting threads that the value has changed
      valueChanged.signalAll();
    } finally {
      lock.unlock();
    }
  }
  public void executeOnValue(E desiredValue, Runnable task)
    throws InterruptedException {
 
    lock.lock();
    try {
      // Checks the value against the desired value
      while (!value.equals(desiredValue)) {
        // This will wait until the value changes
        valueChanged.await();
      }
      // When we get here, the value is correct -- Run the task
      task.run();
    } finally {
      lock.unlock();
    }
  }
  public void append(E value) {
    // Start the pointer at this node
    LinkList<E> node = this;
    node.lock.lock();
    while (node.rest != null) {
      LinkList<E> next = node.rest;
      // Here"s the hand-over-hand locking
      try {
        // Lock the next node
        next.lock.lock();
      } finally {
        // unlock the current node
        node.lock.unlock();
      }
      // Traverse
      node = next;      
    }
    // We"re at the final node, so append and then unlock
    try {
      node.rest = new LinkList<E>(value);
      // Let any waiting threads know that this node"s link has changed
      node.linkChanged.signalAll();
    } finally {
      node.lock.unlock();
    }
  }
  public void printUntilInterrupted(String prefix) {
    // Start the pointer at this node
    LinkList<E> node = this;
    node.lock.lock();
    while (true) {
      LinkList<E> next;
      try {
        System.out.println(prefix + ": " + node.value);
        // Wait for the next node if not available
        while (node.rest == null) {
          node.linkChanged.await();
        }
        // Get the next node
        next = node.rest;
        // Lock it - more hand-to-hand locking
        next.lock.lock();
      } catch (InterruptedException e) {
        // reset the interrupt status
        Thread.currentThread().interrupt();
        return;
      } finally {
        node.lock.unlock();
      }
      // Traverse
      node = next;
    }
  }
}