Android面试多线程 android线程池面试题

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棉花糖 2023-06-12 16:46:30

文章标签 Android面试多线程移动开发面试 java 任务队列 文章分类 代码人生

[color=red][size=xx-large]记不住密码怎么办？[/size][/color] 

[url]http://a.app.qq.com/o/simple.jsp?pkgname=com.wa505.kf.epassword[/url]

[size=x-large][b]1. 线程池结构模型。[/b][/size]
线程池一般情况下需要有三个独立的小模块组成:
a. 任务队列
b. 任务队列协调器
c. 工作线程
下面的图示显示了他们的静态结构图。

[img]http://dl2.iteye.com/upload/attachment/0126/5834/6b81a090-6f21-34cd-868a-80eea9dbd18a.png[/img] 


[size=x-large][b]2. 线程池交互模型。[/b][/size]

下图中显示了其交互模型。
a.客户代码负责入队，
b.工作线程负责loop队列进行工作，同时工作结束后告诉任务队列协调器。
c. 任务队列协调器，协调所有的工作线程和任务队列，使得任务一定可以被执行, 控制线程数目和核心线程数目，同时当客户代码入队时，通知正在wait的工作线程进行工作。

[img]http://dl2.iteye.com/upload/attachment/0126/5836/3b01865d-8904-351d-83c4-79d99871f48f.png[/img] 

[size=x-large][b]3.测试代码[/b][/size]

测试代码进行测试时，模拟一下真实场景。也就是说调用者随机时间点进行调用。执行者的时间也是随机的。

package interview;

public class TestThreadPool {
	static volatile int lastIndex = 0;
	static final int MAX_SLEEP = 3;
	static int runCount = 0;

	public static void main(String[] args) {
		// TODO Auto-generated method stub

		System.out.println("testThreadPoolWithN =============== ");

		testThreadPoolWithN();

		System.out.println("testThreadPoolWith1 =============== ");
		testThreadPoolWith1();
		// System.out.println("count " + count);
	}

	private static void testThreadPoolWith1() {
		ThreadPool threadPool = new ThreadPool(1, 1, 0);

		for (int i = 0; i < 200; ++i) {
			final int index = i;
			randomSleep();
			threadPool.execute(new Runnable() {

				@Override
				public void run() {
					randomSleep();
					assert ((lastIndex + 1) == index);
					lastIndex = index;

					System.out.println("running " + index);
				}

			});

		}
	}

	private static void testThreadPoolWithN() {
		ThreadPool threadPool = new ThreadPool(10, 20, 0);
		for (int i = 0; i < 200; ++i) {
			final int index = i;
			randomSleep();
			threadPool.execute(new Runnable() {
				@Override
				public void run() {
					runCount++;
					randomSleep();

					System.out.println("running " + index);
				}

			});
		}
		assert (runCount == 2000);
	}

	public static void randomSleep() {
		try {
			Thread.sleep((long) (Math.random() * MAX_SLEEP));
		} catch (InterruptedException e1) {

		}
	}

}

[size=x-large][b]3.线程池[/b][/size]

package interview;

import java.util.LinkedList;
import java.util.Queue;

public class ThreadPool {

	private Object mLock = new Object();

	private Queue<Runnable> mQueues = new LinkedList<>();

	private int mCount = 0;

	private int mMaxCount = 3;

	private int mCoreSize = 1;

	private long mNonCoreKeepLiveTime = 0;

	public ThreadPool(int coreSize, int maxSize, long nonCoreKeepLiveTime) {
		mCoreSize = coreSize;
		mMaxCount = maxSize;
		mNonCoreKeepLiveTime = nonCoreKeepLiveTime;
	}

	public int getRunningCount() {
		synchronized (mLock) {
			return mCount;
		}
	}

	private class Worker implements Runnable {

		private Runnable mFirstTask;

		private Worker(Runnable task) {
			mFirstTask = task;
		}

		@Override
		public void run() {
			if (mFirstTask != null) {
				mFirstTask.run();
			}
			while (true) {
				Runnable task;
				synchronized (mLock) {
					task = mQueues.poll();
				}
				if (task != null) {
					task.run();
					continue;
				}
				synchronized (mLock) {
					if (mCount > mCoreSize) {
						try {
							mLock.wait(mNonCoreKeepLiveTime);
						} catch (InterruptedException e) {

						}
						if (mQueues.isEmpty()) {
							break;
						}
					} else {
						try {
							mLock.wait();
						} catch (InterruptedException e) {

						}
					}

				}
			}
			exisWorker(this);
		}
	}

	private void exisWorker(Worker worker) {
		int size;
		synchronized (mLock) {
			mCount--;
			size = mQueues.size();
			int min = mCoreSize;
			if (size > 0 && min == 0) {
				min = 1;
			}
			if (mCount >= min) {
				return;
			}
		}
		addWorker();
	}

	private void addWorker() {
		synchronized (mLock) {
			if (mCount >= mMaxCount) {
				return;
			}
			mCount++;
		}
		Thread thread = new Thread(new Worker(null));
		thread.start();
	}

	public void execute(Runnable runnable) {
		synchronized (mLock) {
			mQueues.add(runnable);
			mLock.notifyAll();
		}
		addWorker();
	}
}

[size=x-large][b]4. 打印结果：[/b][/size]

testThreadPoolWithN =============== 
running 0
running 1
running 3
running 2
running 4
running 5
running 6
running 7
running 8
running 9
running 10
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running 199
testThreadPoolWith1 =============== 
running 0
running 1
running 2
running 3
running 4
running 5
running 6
running 7
running 8
running 9
running 10
running 11
running 12
running 13
running 14
running 15
running 16
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从上面结果可以看出，单线程按照顺序进行执行。而多线程则是无顺序的。

谢谢！

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