使用ExecutorService作为局部变量时，一定要在用完后记得shutDown,否则会出有关问题

ExecutorService 比较重，牵扯到线程，对线程的GC和GC常规对象是有很大的不同

最佳实践，

如果对象提供了shutdown，close等方法，一定要记得在用完后调用这些方法以释放资源，否则会出现资源泄露的情况

package com.qbao.app.test;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * @author chen.kuan 2016年5月17日
 *
 */
public class GCThreadPool {

	public static void main(String[] args) {
		while (true) {
			try {
				ExecutorService service = Executors.newFixedThreadPool(1);
				service.submit(new Runnable() {
					public void run() {
						try {
							Thread.sleep(2);
						} catch (InterruptedException e) {
						}
					}
				});
				service = null;
			} catch (Exception e) {
			}
			try {
				Thread.sleep(2);
			} catch (InterruptedException e) {
			}
		}
	}

}

================

可以看到线程数量直线上升，（线程泄露）最后出现无法new新线程的情况

Exception in thread "main" java.lang.OutOfMemoryError: unable to create new native thread
	at java.lang.Thread.start0(Native Method)
	at java.lang.Thread.start(Thread.java:714)
	at java.util.concurrent.ThreadPoolExecutor.addWorker(ThreadPoolExecutor.java:950)
	at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1357)
	at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:112)
	at com.qbao.app.test.GCThreadPool.main(GCThreadPool.java:16)

 ------------------

加入shutdown之后，问题解决

package com.qbao.app.test;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * @author chen.kuan 2016年5月17日
 *
 */
public class GCThreadPool {

	public static void main(String[] args) {

		while (true) {
			try {
				ExecutorService service = Executors.newFixedThreadPool(1);
				service.submit(new Runnable() {
					public void run() {
						try {
							Thread.sleep(2);
						} catch (InterruptedException e) {
						}
					}
				});
				service.shutdown();
				service = null;
			} catch (Exception e) {
			}
			try {
				Thread.sleep(10);
			} catch (InterruptedException e) {
			}
		}
	}

}