Java 并发编程之任务取消（六）

关闭ExecutorService

ExecutorService提供了两种关闭方法，使用Shutdown正常关闭，以及使用ShutdownNow强行关闭。在进行强行关闭时，shutdownNow首先关闭当前正在执行的任务。然后返回所有尚未启动的任务清单 。

返回未启动任务清单这句没明白返回的方式，于是去查看了一下源码

    /**     * Attempts to stop all actively executing tasks, halts the     * processing of waiting tasks, and returns a list of the tasks     * that were awaiting execution.     *     * <p>This method does not wait for actively executing tasks to     * terminate.  Use {@link #awaitTermination awaitTermination} to     * do that.     *     * <p>There are no guarantees beyond best-effort attempts to stop     * processing actively executing tasks.  For example, typical     * implementations will cancel via {@link Thread#interrupt}, so any     * task that fails to respond to interrupts may never terminate.     *     * @return list of tasks that never commenced execution     * @throws SecurityException if a security manager exists and     *         shutting down this ExecutorService may manipulate     *         threads that the caller is not permitted to modify     *         because it does not hold {@link     *         java.lang.RuntimePermission}{@code ("modifyThread")},     *         or the security manager's {@code checkAccess} method     *         denies access.     */    List<Runnable> shutdownNow();

是用List的形式返回submit的Runnable

还是像上一篇一样使用日志服务做为栗子

import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.RejectedExecutionException;import java.util.concurrent.TimeUnit;public class LogService {private final ExecutorService exec = Executors.newSingleThreadExecutor();private final int TIMEOUT = 100;...public void start() {}public void stop() throws InterruptedException {try {exec.shutdown();exec.awaitTermination(TIMEOUT, TimeUnit.MILLISECONDS);} finally {writer.close();}}public void log(String msg){try{exec.execute(new writerTask(msg)));}catch(RejectedExecutionException ignored){}}}

省略了部分代码。因为和上一篇中的代码都一样，主要展现的是利用ExecutorService后Stop方法修改后的样子

毒丸对象

这是另一种消费者生产者的栗子，毒丸是指一个放在队列上的对象 ，其作用是当得到这个对象的时候，立即停止。在FIFO队列中，毒丸对象 将确保消费者在关闭之前首先完成队列中的所有工作。

举个栗子。。。哦。。花了好长时间才调试好。。

import java.io.File;import java.io.FileFilter;import java.util.concurrent.BlockingQueue;import java.util.concurrent.LinkedBlockingQueue;public class InderXingService {private static final File POISON = new File("");private final IndexerThread consumer = new IndexerThread();private final CrawlerThread producer = new CrawlerThread();private final BlockingQueue<File> queue = new LinkedBlockingQueue<File>();private final FileFilter fileFilter;private final File root = new File("F://Desktop/Open");public static void main(String[] args) {InderXingService index = new InderXingService(null, null);index.start();}public InderXingService(FileFilter fileFilter, File root) {this.fileFilter = fileFilter;}public void start() {producer.start();consumer.start();}public void stop() {producer.interrupt();}public void awaitTermination() throws InterruptedException {consumer.join();}class CrawlerThread extends Thread {@Overridepublic void run() {// TODO Auto-generated method stubtry {crawl(root);} catch (InterruptedException e) {e.printStackTrace();} finally {System.out.println("putpoison");while (true) {try {queue.put(POISON);break;} catch (InterruptedException e1) {}}}}private void crawl(File root) throws InterruptedException {// 为文件添加内容File[] entries = root.listFiles();if (entries != null) {for (File entry : entries) {if (entry.isDirectory()) {crawl(entry.getAbsoluteFile());} else if (!alreadindex(entry)) {queue.put(entry);}}}}private boolean alreadindex(File entry) {// TODO Auto-generated method stubif (queue.contains(entry)) {return true;}return false;}}class IndexerThread extends Thread {@Overridepublic void run() {while (true) {File file;try {file = queue.take();if (file == POISON) {break;} else {indexFile(file);}} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}private void indexFile(File root) throws InterruptedException {System.out.println(root.getName());}}}

这个是遍历一个目录的文件的栗子-0-

刚才试着遍历了一下整个F盘。。貌似消费者跟的上。而且没啥压力看来都可以用了

public static void main(String[] args) {InderXingService index = new InderXingService(null, null);index.start();try {Thread.sleep(1000);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}index.stop();}

试了一下中断方法

UpgradeReport.xslt
UpgradeReport_Minus.gif
UpgradeReport_Plus.gif
java.lang.InterruptedException
putpoison
    at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireInterruptibly(Unknown Source)
    at java.util.concurrent.locks.ReentrantLock.lockInterruptibly(Unknown Source)
    at java.util.concurrent.LinkedBlockingQueue.put(Unknown Source)
    at InderXingService$CrawlerThread.crawl(InderXingService.java:73)
    at InderXingService$CrawlerThread.crawl(InderXingService.java:71)
    at InderXingService$CrawlerThread.crawl(InderXingService.java:71)
    at InderXingService$CrawlerThread.crawl(InderXingService.java:71)
    at InderXingService$CrawlerThread.crawl(InderXingService.java:71)
    at InderXingService$CrawlerThread.crawl(InderXingService.java:71)
    at InderXingService$CrawlerThread.crawl(InderXingService.java:71)
    at InderXingService$CrawlerThread.run(InderXingService.java:49)

结果也对。

使用毒丸君的注意事顶：

只有在生产者和消费者的数量都已知的情况下，才可以使用毒丸对象。当生产者多的时候 ，可以加一个计数器，当所有生产者的丸子都放在队列里边的时候再进行打断。多消费者的时候 ，一个生产者可以放入与消费者数量相同的丸子。因为每个消费者都只能接收一个丸子。当两者数量都比较大时就不太好用了。只有在无界队列中。毒丸对象才能可靠的工作