operationsqueue.java

实现图片的显示功能的J2ME程序

// Copyright 2004 Nokia Corporation.
//
// THIS SOURCE CODE IS PROVIDED 'AS IS', WITH NO WARRANTIES WHATSOEVER,
// EXPRESS OR IMPLIED, INCLUDING ANY WARRANTY OF MERCHANTABILITY, FITNESS
// FOR ANY PARTICULAR PURPOSE, OR ARISING FROM A COURSE OF DEALING, USAGE
// OR TRADE PRACTICE, RELATING TO THE SOURCE CODE OR ANY WARRANTY OTHERWISE
// ARISING OUT OF ANY PROPOSAL, SPECIFICATION, OR SAMPLE AND WITH NO
// OBLIGATION OF NOKIA TO PROVIDE THE LICENSEE WITH ANY MAINTENANCE OR
// SUPPORT. FURTHERMORE, NOKIA MAKES NO WARRANTY THAT EXERCISE OF THE
// RIGHTS GRANTED HEREUNDER DOES NOT INFRINGE OR MAY NOT CAUSE INFRINGEMENT
// OF ANY PATENT OR OTHER INTELLECTUAL PROPERTY RIGHTS OWNED OR CONTROLLED
// BY THIRD PARTIES
//
// Furthermore, information provided in this source code is preliminary,
// and may be changed substantially prior to final release. Nokia Corporation
// retains the right to make changes to this source code at
// any time, without notice. This source code is provided for informational
// purposes only.
//
// Nokia and Nokia Connecting People are registered trademarks of Nokia
// Corporation.
// Java and all Java-based marks are trademarks or registered trademarks of
// Sun Microsystems, Inc.
// Other product and company names mentioned herein may be trademarks or
// trade names of their respective owners.
//
// A non-exclusive, non-transferable, worldwide, limited license is hereby
// granted to the Licensee to download, print, reproduce and modify the
// source code. The licensee has the right to market, sell, distribute and
// make available the source code in original or modified form only when
// incorporated into the programs developed by the Licensee. No other
// license, express or implied, by estoppel or otherwise, to any other
// intellectual property rights is granted herein.
import java.util.*;

// Simple Operations Queue
// It runs in an independent thread and executes Operations serially
class OperationsQueue implements Runnable
{

  private volatile boolean running = true;
  private final Vector operations = new Vector();


  OperationsQueue()
  {
    // Notice that all operations will be done in another
    // thread to avoid deadlocks with GUI thread
    new Thread(this).start();
  }


  void enqueueOperation(Operation nextOperation)
  {
    operations.addElement(nextOperation);
    synchronized (this)
    {
      notify();
    }
  }


  // stop the thread
  void abort()
  {
    running = false;
    synchronized (this)
    {
      notify();
    }
  }


  public void run()
  {
    while (running)
    {
      while (operations.size() > 0)
      {
        try
        {
          // execute the first operation on the queue
          ((Operation) operations.firstElement()).execute();
        }
        catch (Exception e)
        {
          // Nothing to do. It is expected that each operations handle
          // their own locally exception but this block is to ensure
          // that the queue continues to operate
        }
        operations.removeElementAt(0);
      }
      synchronized (this)
      {
        try
        {
          wait();
        }
        catch (InterruptedException e)
        {
          // it doesn't matter
        }
      }
    }
  }

}