多线程入门

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多线程

Java thread 多线程

一直只是看看多线程有关的东西，项目中用的时候也只是网上查查，能work就好，而没有真正去研究过。所以这次打算好好看一下。。。
------------------------ 我是分割线 ------------------------------
一个简单的多线程程序：

public class MyThread {

	private List<Thread> threads = new ArrayList<Thread>();

	public Thread makeThread() {
		Runnable runnable = new Runnable() {
			@Override
			public void run() {
				int i = 0;
				while (true) {
					System.out.println(Thread.currentThread().getName() + ": " + i++);
					try {
						Thread.sleep(100);
					} catch (InterruptedException e) {
						return;
					}
				}
			}
		};

		return new Thread(runnable);
	}

	public synchronized void start() {
		for (int i = 0; i < 10; i++) {
			MyThread th = new MyThread();
			threads.add(th.makeThread());
		}
		for (Thread t : threads)
			t.start();
	}

	public synchronized void stop() {
		for (Thread t : threads)
			t.interrupt();
		threads.clear();
	}

	public static void main(String[] args) throws InterruptedException {
		System.out.println("All threads will start and end in 1 second...");
		System.out.println(new Date());
		MyThread mt = new MyThread();
		mt.start();
		Thread.sleep(1000 * 1);
		mt.stop();
		System.out.println(new Date());
	}
}

其某一次运行结果是：

引用

All threads will start and end in 1 second...
Tue Jul 19 14:11:47 CST 2011
Thread-0: 0
Thread-1: 0
Thread-2: 0
Thread-3: 0
Thread-4: 0
Thread-6: 0
Thread-5: 0
Thread-7: 0
Thread-8: 0
Thread-9: 0
Thread-2: 1
Thread-1: 1
Thread-6: 1
Thread-0: 1
Thread-4: 1
Thread-3: 1
Thread-7: 1
Thread-5: 1
Thread-9: 1
Thread-8: 1
Thread-2: 2
Thread-5: 2
Thread-7: 2
Thread-1: 2
Thread-6: 2
Thread-4: 2
Thread-0: 2
Thread-3: 2
Thread-9: 2
Thread-8: 2
Thread-2: 3
Thread-4: 3
Thread-6: 3
Thread-0: 3
Thread-5: 3
Thread-7: 3
Thread-1: 3
Thread-3: 3
Thread-8: 3
Thread-9: 3
Thread-1: 4
Thread-3: 4
Thread-0: 4
Thread-6: 4
Thread-7: 4
Thread-5: 4
Thread-2: 4
Thread-4: 4
Thread-9: 4
Thread-8: 4
Thread-3: 5
Thread-6: 5
Thread-2: 5
Thread-5: 5
Thread-7: 5
Thread-1: 5
Thread-0: 5
Thread-4: 5
Thread-8: 5
Thread-9: 5
Thread-2: 6
Thread-0: 6
Thread-4: 6
Thread-6: 6
Thread-1: 6
Thread-7: 6
Thread-5: 6
Thread-3: 6
Thread-8: 6
Thread-9: 6
Thread-2: 7
Thread-4: 7
Thread-0: 7
Thread-3: 7
Thread-7: 7
Thread-1: 7
Thread-5: 7
Thread-6: 7
Thread-8: 7
Thread-9: 7
Thread-2: 8
Thread-5: 8
Thread-1: 8
Thread-7: 8
Thread-3: 8
Thread-6: 8
Thread-0: 8
Thread-4: 8
Thread-9: 8
Thread-8: 8
Thread-5: 9
Thread-7: 9
Thread-2: 9
Thread-0: 9
Thread-1: 9
Thread-4: 9
Thread-6: 9
Thread-3: 9
Thread-8: 9
Thread-9: 9
Tue Jul 19 14:11:48 CST 2011

可以从运行结果中看出，除了我们第一次启动的时候由于for的原因，线程的启动是有序的。但一旦线程启动之后，其优先级就不是我们可控的了。

------------------------- 我是分隔线 -----------------------------
虽然我们可以同过setPriority方法来设置线程的优先级，但是当线程数量不够多，也就是说系统资源充足的时候很难看出优先级的存在。通常的JVM实现都会在线程数目超过能使用的CPU数目时，都会优先选择优先级比较高的线程运行。
一下程序是在上面实例的基础上加了优先级，感官上没什么区别：


private int[] pri = new int[] { 1, 5, 10 };
private final Random r = new Random();

while (true) {
	System.out.println(Thread.currentThread().getName() + "(Priority = " + Thread.currentThread().getPriority() + "): "
			+ i++);
	try {
		Thread.sleep(100);
	} catch (InterruptedException e) {
		return;
	}
}

...

// Set priority
Thread t = new Thread(runnable);
t.setPriority(pri[r.nextInt(3)]);

...

运行结果：

引用

All threads will start and end in 1 second...
Tue Jul 19 14:47:11 CST 2011
Thread-0(Priority = 10): 0
Thread-2(Priority = 5): 0
Thread-1(Priority = 5): 0
Thread-3(Priority = 5): 0
Thread-4(Priority = 1): 0
Thread-7(Priority = 10): 0
Thread-5(Priority = 1): 0
Thread-9(Priority = 10): 0
Thread-6(Priority = 1): 0
Thread-8(Priority = 1): 0
Thread-2(Priority = 5): 1
Thread-0(Priority = 10): 1
Thread-7(Priority = 10): 1
Thread-1(Priority = 5): 1
Thread-3(Priority = 5): 1
Thread-4(Priority = 1): 1
Thread-5(Priority = 1): 1
Thread-9(Priority = 10): 1
Thread-8(Priority = 1): 1
Thread-6(Priority = 1): 1
Thread-7(Priority = 10): 2
Thread-2(Priority = 5): 2
Thread-0(Priority = 10): 2
Thread-3(Priority = 5): 2
Thread-1(Priority = 5): 2
Thread-4(Priority = 1): 2
Thread-6(Priority = 1): 2
Thread-8(Priority = 1): 2
Thread-5(Priority = 1): 2
Thread-9(Priority = 10): 2
Thread-0(Priority = 10): 3
Thread-3(Priority = 5): 3
Thread-7(Priority = 10): 3
Thread-2(Priority = 5): 3
Thread-1(Priority = 5): 3
Thread-4(Priority = 1): 3
Thread-9(Priority = 10): 3
Thread-5(Priority = 1): 3
Thread-6(Priority = 1): 3
Thread-8(Priority = 1): 3
Thread-7(Priority = 10): 4
Thread-1(Priority = 5): 4
Thread-3(Priority = 5): 4
Thread-0(Priority = 10): 4
Thread-2(Priority = 5): 4
Thread-4(Priority = 1): 4
Thread-9(Priority = 10): 4
Thread-5(Priority = 1): 4
Thread-8(Priority = 1): 4
Thread-6(Priority = 1): 4
Thread-1(Priority = 5): 5
Thread-2(Priority = 5): 5
Thread-3(Priority = 5): 5
Thread-0(Priority = 10): 5
Thread-7(Priority = 10): 5
Thread-9(Priority = 10): 5
Thread-8(Priority = 1): 5
Thread-6(Priority = 1): 5
Thread-4(Priority = 1): 5
Thread-5(Priority = 1): 5
Thread-1(Priority = 5): 6
Thread-3(Priority = 5): 6
Thread-2(Priority = 5): 6
Thread-0(Priority = 10): 6
Thread-7(Priority = 10): 6
Thread-9(Priority = 10): 6
Thread-8(Priority = 1): 6
Thread-4(Priority = 1): 6
Thread-5(Priority = 1): 6
Thread-6(Priority = 1): 6
Thread-1(Priority = 5): 7
Thread-0(Priority = 10): 7
Thread-2(Priority = 5): 7
Thread-3(Priority = 5): 7
Thread-7(Priority = 10): 7
Thread-9(Priority = 10): 7
Thread-4(Priority = 1): 7
Thread-5(Priority = 1): 7
Thread-8(Priority = 1): 7
Thread-6(Priority = 1): 7
Thread-0(Priority = 10): 8
Thread-3(Priority = 5): 8
Thread-2(Priority = 5): 8
Thread-1(Priority = 5): 8
Thread-9(Priority = 10): 8
Thread-7(Priority = 10): 8
Thread-4(Priority = 1): 8
Thread-6(Priority = 1): 8
Thread-8(Priority = 1): 8
Thread-5(Priority = 1): 8
Thread-0(Priority = 10): 9
Thread-1(Priority = 5): 9
Thread-3(Priority = 5): 9
Thread-2(Priority = 5): 9
Thread-7(Priority = 10): 9
Thread-9(Priority = 10): 9
Thread-8(Priority = 1): 9
Thread-4(Priority = 1): 9
Thread-6(Priority = 1): 9
Thread-5(Priority = 1): 9
Tue Jul 19 14:47:12 CST 2011

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