Java并发学习之十九——线程同步工具之Phaser

本文是学习网络上的文章时的总结。感谢大家无私的分享。

JDK 1.7 加入了一个新的工具Phaser。Phaser的在功能上与CountDownLatch有部分重合。

以下使用Phaser类来同步3个并发任务。

这3个任务会在3个不同的目录和它们的子目录中搜索扩展名是.log的文件。

这个任务被分成3个步骤：

1. 在指定的目录和子目录中获得文件扩展名为.log的文件列表。

       2. 在操控台打印结果。

在步骤1和步骤2的结尾我们要检查列表是否为空。

假设为空。那么线程直接结束执行并从phaser类中淘汰。

package chapter3;

import java.io.File;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.concurrent.Phaser;
import java.util.concurrent.TimeUnit;

public class FileSearch implements Runnable{

	private String initPath;
	private String end;
	private List<String> results;

	private Phaser phaser;

	public FileSearch(String initPath,String end,Phaser phaser ){
		this.initPath = initPath;
		this.end = end;
		this.phaser = phaser;
		this.results = new ArrayList<String>();
	}

	private void directoryProcess(File file){
		File list[] = file.listFiles();
		if(list != null){
			for(int i = 0;i< list.length;i++){
				if(list[i].isDirectory()
						){
					directoryProcess(list[i]);
				}else{
					fileProcess(list[i]);
				}
			}
		}
	}
	private void fileProcess(File file){
		if(file.getName().endsWith(end)){
			results.add(file.getAbsolutePath());
		}
	}

	private void filterResults(){
		List<String> newResults = new ArrayList<String>();
		long actualDate = new Date().getTime();
		for (int i = 0; i < results.size(); i++) {
			File file = new File(results.get(i));
			long fileDate = file.lastModified();
			if(actualDate-fileDate<TimeUnit.MILLISECONDS.convert(1, TimeUnit.DAYS)){
				newResults.add(results.get(i));
			}
		}
		results = newResults;
	}

	private boolean checkResults(){
		if(results.isEmpty()){
			System.out.printf("%s: Phase %d: 0 results.\n", Thread
					.currentThread().getName(), phaser.getPhase());
					System.out.printf("%s: Phase %d: End.\n", Thread.currentThread()
					.getName(), phaser.getPhase());
					phaser.arriveAndDeregister();
			return false;

		}else{
			System.out.printf("%s: Phase %d: %d results.\n", Thread
					.currentThread().getName(), phaser.getPhase(), results
					.size());
					phaser.arriveAndAwaitAdvance();
			return true;
		}
	}

	private void showInfo(){
		for (int i = 0; i < results.size(); i++) {
			File file = new File(results.get(i));
			System.out.printf("%s: %s\n", Thread.currentThread().getName(),
					file.getAbsolutePath());

		}
		phaser.arriveAndAwaitAdvance();
	}

	@Override
	public void run() {
		phaser.arriveAndAwaitAdvance();
		System.out.printf("%s: Starting.\n", Thread.currentThread().getName());

		File file = new File(initPath);
		if(file.isDirectory()){
			directoryProcess(file);
		}
		if(!checkResults()){
			return ;
		}
		filterResults();
		if(!checkResults()){
			return;
		}
		showInfo();
		phaser.arriveAndDeregister();
		System.out.printf("%s: Work completed.\n", Thread.currentThread()
				.getName());

	}

}

package chapter3;

import java.util.concurrent.Phaser;

public class Main5 {

	/**
	 * <p>
	 * </p>
	 * @author zhangjunshuai
	 * @date 2014-9-29 下午4:31:46
	 * @param args
	 */
	public static void main(String[] args) {
		Phaser phaser = new Phaser(3);

		FileSearch system = new FileSearch("C:\\Windows","log",phaser);
		FileSearch apps = new FileSearch("c:\\Program Files","log",phaser);
		FileSearch documents = new FileSearch("c:\\Documents And Settings","log",phaser);

		Thread systemThread = new Thread(system,"System");
		systemThread.start();

		Thread appsThread = new Thread(apps,"apps");
		appsThread.start();

		Thread documentsThread = new Thread(documents,"documents");
		documentsThread.start();

		try {
			systemThread.join();
			appsThread.join();
			documentsThread.join();
		} catch (Exception e) {
			e.printStackTrace();
		}

		System.out.println("Terminated: " + phaser.isTerminated());

	}

}

执行结果