资源管理的测试

先摆上昨天测试用的栗子

import java.util.concurrent.Semaphore;

public class BoundedBuffer<E> {

	private final Semaphore availableItems, availableSpaces;
	private final E[] Items;
	private int putPosition = 0, takePosition = 0;

	public BoundedBuffer(int capacity) {
		availableItems = new Semaphore(0);
		availableSpaces = new Semaphore(capacity);
		Items = (E[]) new Object[capacity];
	}

	public boolean isEmpty() {
		return availableItems.availablePermits() == 0;
	}

	public boolean isFull() {
		return availableSpaces.availablePermits() == 0;
	}

	public void put(E x) throws InterruptedException {
		availableSpaces.acquire();
		doInsert(x);
		availableItems.release();
	}

	public E take() throws InterruptedException {
		availableItems.acquire();
		E item = doExtra();
		availableSpaces.release();
		return item;
	}

	private synchronized void doInsert(E x) {
		// TODO Auto-generated method stub
		int i = putPosition;
		Items[i] = x;
		putPosition = (++i == Items.length) ? 0 : i;
	}

	private synchronized E doExtra() {
		int i = takePosition;
		E x = Items[i];
		Items[i] = null;
		takePosition = (++i == Items.length) ? 0 : i;
		return x;
	}

}

通过一些测量应用程序中内存使用情况 的堆检查 工具，可以很容易地测试出对内存的不合理占用。许多商业和开源的堆分析工具中都支持这种功能 。

import static org.junit.Assert.assertTrue;
import junit.framework.Test;

public class PutTakeTest {
	final int CAPACITY = 1000;

	class Big {
		double[] big = new double[10000];
	}

	public static void main(String[] args) throws InterruptedException {
		new PutTakeTest().testLeak();
	}

	void testLeak() throws InterruptedException {
		BoundedBuffer<Big> bb = new BoundedBuffer<PutTakeTest.Big>(CAPACITY);
		long heapsize1 = Runtime.getRuntime().totalMemory();
		for (int i = 0; i < CAPACITY; i++) {
			bb.put(new Big());
		}
		for (int i = 0; i < CAPACITY; i++) {
			bb.take();
		}
		long heapsize2 = Runtime.getRuntime().totalMemory();
		System.out.println(heapsize1 + "\n" + heapsize2);
	}
}

不过在我实际测试的过程中，两次内存用量在将元素的引用置为空的条件下还是明显的不同，应该是没有触发system.gc。但是我们无法强制去触发垃圾回收。。所以这个测试在技术上还是有点问题的。可能对选择的垃圾收集器也有要求。我用的是CMS并且设置在内存占用达到75%才触发FullGC。

使用回调

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicInteger;

import javax.management.MXBean;

import org.junit.experimental.max.MaxCore;

import static org.junit.Assert.*;

public class TestingThreadFactory implements ThreadFactory {
	public final AtomicInteger numCreated = new AtomicInteger();
	private final ThreadFactory factory = Executors.defaultThreadFactory();

	public static void main(String[] args) {
		try {
			new TestingThreadFactory().testPoolExpansion();
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

	@Override
	public Thread newThread(Runnable r) {
		// TODO Auto-generated method stub
		numCreated.incrementAndGet();
		return factory.newThread(r);
	}

	public void testPoolExpansion() throws InterruptedException {
		int MAX_SIZE = 10;
		TestingThreadFactory threadFactory = new TestingThreadFactory();
		ExecutorService exec = Executors.newFixedThreadPool(MAX_SIZE,
				threadFactory);
		for (int i = 0; i < 10 * MAX_SIZE; i++) {
			exec.execute(new Runnable() {
				public void run() {
					try {
						Thread.sleep(Long.MAX_VALUE);
					} catch (InterruptedException e) {
						// TODO Auto-generated catch block
						Thread.currentThread().interrupt();
					}
				}
			});
		}
		for (int i = 0; i < 20 && threadFactory.numCreated.get() < MAX_SIZE; i++) {
			Thread.sleep(100);
		}
		assertEquals(threadFactory.numCreated.get(), MAX_SIZE);
		System.out.println(threadFactory.numCreated.get());
		exec.shutdown();
	}
}

在测试线程时，有以下几点，在需要更多的线程时创建新线程，在不需要时不创建 ，以及当需要回收空闲线程时执行回收操作等 。

程序中让线程进行长时间的睡眠是因为测试当把一些运行时间较长的任务提前给线程池时，线程池中的任务数量在长时间内都不会变化，这就可以进行一些判断，例如当测试线程池是否能够按照预期方式进行扩展 。

Java 并发编程之测试（二）