Timer的实现机制

Timer使用线程机制来实现，每个Timer对象后有一个后台线程，这个后台线程来执行该Timer对象的所用TimeTask任务。

Timer代码中有后台线程实例：

    
/**
     * The timer task queue.  This data structure is shared with the timer
     * thread.  The timer produces tasks, via its various schedule calls,
     * and the timer thread consumes, executing timer tasks as appropriate,
     * and removing them from the queue when they're obsolete.
     */
    private TaskQueue queue = new TaskQueue();

    /**
     * The timer thread.
     */
    private TimerThread thread = new TimerThread(queue);

这就是一个生产者消费者模式，Timer生产TimerTask任务放到TaskQueue 中，然后TimerThread从这个TaskQueue中取任务来进行执行。


A facility for threads to schedule tasks for future execution in a
background thread.  Tasks may be scheduled for one-time execution, or for repeated execution at regular intervals.

Corresponding to each Timer object is a single background
thread that is used to execute all of the timer's tasks, sequentially. Timer tasks should complete quickly.

		Timer t = new Timer();	
		Calendar date1 = Calendar.getInstance();
		date1.add(Calendar.MILLISECOND, 1000);
		t.schedule(new TimerTask(){
			@Override
			public void run() {
				System.out.println("3");
				System.out.println("线程t1:" + Thread.currentThread().getId());
			}			
		}, date1.getTime());
		
		
		Timer t2 = new Timer();	
		Calendar date2 = Calendar.getInstance();
		date2.add(Calendar.MILLISECOND, 1000);
		t2.schedule(new TimerTask(){
			@Override
			public void run() {
				System.out.println("4");
				System.out.println("线程t2:" + Thread.currentThread().getId());
			}			
		}, date2.getTime());	
		
		System.out.println("主线程：" + Thread.currentThread().getId());
		System.out.println("1");	

输出：
主线程：1
1
3
4
线程t1:8
线程t2:9