Java多线程饥饿与公平介绍及代码示例

public class ThreadDeadlock {
	ExecutorService exec = Executors.newSingleThreadScheduledExecutor();
	//  ExecutorService exec = Executors.newCachedThreadPool();  //如果添加给线程池中添加足够多的线程，就可以让所有任务都执行，避免饥饿死锁。 
	/** 
   * 模拟页面加载的例子 
   * 
   * 产生死锁分析： 
   * RenderPageTask任务中有2个子任务分别是“加载页眉”和“加载页脚”。当提交RenderPageTask任务时，实际上是向线程池中添加了3个任务， 
   * 但是由于线程池是单一线程池，同时只会执行一个任务，2个子任务就会在阻塞在线程池中。而RenderPageTask任务由于得不到返回，也会 
   * 一直堵塞，不会释放线程资源让子线程执行。这样就导致了线程饥饿死锁。 
   * 
   * 在一个Callable任务中，要返回2个子任务 
   * @author hadoop 
   * 
   */
	class RenderPageTask implements Callable<String>{
		@Override 
		    public String call() throws Exception {
			Future<String> header,footer;
			header = exec.submit(new Callable<String>(){
				@Override 
				        public String call() throws Exception {
					System.out.println("加载页眉");
					Thread.sleep(2*1000);
					return "页眉";
				}
			}
			);
			footer = exec.submit(new Callable<String>(){
				@Override 
				        public String call() throws Exception {
					System.out.println("加载页脚");
					Thread.sleep(3*1000);
					return "页脚";
				}
			}
			);
			System.out.println("渲染页面主体");
			return header.get() + footer.get();
		}
	}
	public static void main(String[] args) throws InterruptedException, ExecutionException {
		ThreadDeadlock td = new ThreadDeadlock();
		Future<String> futre = td.exec.submit(td.new RenderPageTask());
		String result = futre.get();
		System.out.println("执行结果为：" + result);
	}
}

public class Synchronizer{
  public synchronized void doSynchronized(){
  //do a lot of work which takes a long time
  }
}

public class Synchronizer{
  Lock lock = new Lock();
  public void doSynchronized() throws InterruptedException{
    this.lock.lock();
    //critical section, do a lot of work which takes a long time
    this.lock.unlock();
  }
}

public class Lock{
	private Boolean isLocked   = false;
	private Thread lockingThread = null;
	public synchronized void lock() throws InterruptedException{
		while(isLocked){
			wait();
		}
		isLocked = true;
		lockingThread = Thread.currentThread();
	}
	public synchronized void unlock(){
		if(this.lockingThread != Thread.currentThread()){
			throw new IllegalMonitorStateException(
			       "Calling thread has not locked this lock");
		}
		isLocked = false;
		lockingThread = null;
		notify();
	}
}

public class FairLock {
	private Boolean      isLocked    = false;
	private Thread      lockingThread = null;
	private List<QueueObject> waitingThreads =
	      new ArrayList<QueueObject>();
	public void lock() throws InterruptedException{
		QueueObject queueObject      = new QueueObject();
		Boolean   isLockedForThisThread = true;
		synchronized(this){
			waitingThreads.add(queueObject);
		}
		while(isLockedForThisThread){
			synchronized(this){
				isLockedForThisThread =
				      isLocked || waitingThreads.get(0) != queueObject;
				if(!isLockedForThisThread){
					isLocked = true;
					waitingThreads.remove(queueObject);
					lockingThread = Thread.currentThread();
					return;
				}
			}
			try{
				queueObject.doWait();
			}
			catch(InterruptedException e){
				synchronized(this) {
					waitingThreads.remove(queueObject);
				}
				throw e;
			}
		}
	}
	public synchronized void unlock(){
		if(this.lockingThread != Thread.currentThread()){
			throw new IllegalMonitorStateException(
			    "Calling thread has not locked this lock");
		}
		isLocked   = false;
		lockingThread = null;
		if(waitingThreads.size() > 0){
			waitingThreads.get(0).doNotify();
		}
	}
}

public class QueueObject {
	private Boolean isNotified = false;
	public synchronized void doWait() throws InterruptedException {
		while(!isNotified){
			this.wait();
		}
		this.isNotified = false;
	}
	public synchronized void doNotify() {
		this.isNotified = true;
		this.notify();
	}
	public Boolean equals(Object o) {
		return this == o;
	}
}