java - 同步块(synchronized block)和方法未按预期工作

Question

状态:在方法中添加static，变量队列并使synchronized(crawler.class)解决问题。谢谢大家!!

http://pastie.org/8724549#41-42,46,49,100-101,188-189,191

突出显示的方法/ block 是同步。

该 block /方法应该在特定时间由一种方法访问。。

应该是这样的 = 第一个线程进入方法，更新大小，所有其他线程看到那个大小。更新了一个。更新应该只由第一个线程进行。不是别人

1. 为什么要运行它。它由所有 11 个线程运行。
2. 它正在运行而不等待前面的线程完成。 "queue loaded, new size --------------"its creating/adding elements

package crawler;

import crawler.Main;
import static crawler.Main.basicDAO;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.ConcurrentMap;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.select.Elements;


/**
 *
 * @author syncsys
 */
public class Crawler implements Runnable, InterfaceForConstants {
public static final String patternString = "[_A-Za-z0-9-]+(\\.[_A-Za-z0-9-]+)*@[A-Za-z0-9]+(\\.[A-Za-z0-9]+)*(\\.[A-Za-z]{2,})";
public ConcurrentLinkedQueue<Link> queue =  new ConcurrentLinkedQueue<Link>();
private volatile String url;





    private void crawl(String url) {


        synchronized (Crawler.class){
            System.out.println("queue size "+queue.size());
            if(queue.size() < (totalSizeOfEmailBucket / 3)){
                updateQueue();
            }
        System.out.println("This is inside of sync block.   -----------    queue size "+queue.size());
        }
        System.out.println("This is at the end of sync block.   -----------    queue size "+queue.size());





        BufferedReader bf = null;
        try {
            url = queue.poll().getLink();
            URL target = new URL(url);
            bf = new BufferedReader(
                    new InputStreamReader(target.openStream())
                 );
            StringBuilder html = new StringBuilder();
            String inputLine;
            while ((inputLine = bf.readLine()) != null) {
                html.append(inputLine);
            }
            List emailList = new ArrayList( getEmailList(html.toString()) );
           // List linkList = new ArrayList( getLinkList(html.toString(), url) );
            System.out.println("Just worked on --------- "+ url);
            Main.processedLinksCount++;
            if(emailList.size()>0){
                putEmailsInDB(emailList);
            }

            // putLinksInDB(linkList);
        } catch (IOException ex) {
            Logging.logError(ex.toString());
            basicDAO.deleteLink(url);
        } catch (Exception ex) {
            Logging.logError(ex.toString()); 
            basicDAO.deleteLink(url);
        }finally{
            if(bf !=null){
                try {
                bf.close();
                } catch (IOException ex) {
                    Logging.logError(ex.toString());
                }

            }
            crawl(null);
        }
    }

    public synchronized void  updateQueue() {



            Queue<Link> tempQueue =  new PriorityQueue<Link>();
            tempQueue = getNonProcessedLinkFromDB() ;

            queue.addAll(tempQueue);
            BasicDAO.markLinkAsProcesed(tempQueue);
            System.out.println("queue loaded, new  size ------------------------------------ "+queue.size());

    }

    private  List getLinkList(String html, String url) {
        Document doc = Jsoup.parse(html);
        Elements bodies = doc.select("body");
        List linkList =  new ArrayList();
        for(Element body : bodies ){
            Elements aTags = body.getElementsByTag("a");
            for (Element a: aTags){
               String link =  a.attr("href");
               if ( !(link.startsWith("#")) 
                     && 
                    !(link.contains("()"))
                     && 
                    !(link.endsWith(".jpg")) 
                     && 
                    !(link.endsWith(".jpeg"))  
                     && 
                    !(link.endsWith(".png"))  
                     && 
                    !(link.endsWith(".gif"))     ){

                    if( link.startsWith("/") ){
                        link = url+link;
                    }
                 linkList.add(link);
                 //put link in db
               }    
            }
        }

        return linkList;
    }

    private  List getEmailList(String html) {
        Pattern p = Pattern.compile(patternString);
        Matcher m = p.matcher(html);
        List emailList = new ArrayList();
        while(m.find()){
            emailList.add(m.group());
            Main.nonUniqueEmailsCount++;
        }

        return emailList;    
    }



    private Queue<Link> getNonProcessedLinkFromDB() {
        return ( basicDAO.getNonProcessedLink() );
    }

    private  void putEmailsInDB(List emailList) {
        basicDAO.insertEmail(emailList);
    }

    private  void putLinksInDB(List linkList) {
       basicDAO.insertLinks(linkList);
    }

    @Override
    public void run() {
        if(url != null){
            crawl(url);
        }else{
 //          crawl();
        }

    }
    public Crawler(String url){
        this.url = url;
    }

    public Crawler(){
        this.url =  null;
    }
}

线程启动方式:不乐观。我知道。未使用执行程序服务或池，但以下是有效代码:

for (int i = 0; i < 11; i++) {


                    try {



                             Thread thread = new Thread(new Crawler("https://www.google.com.pk/?gws_rd=cr&ei=-q8vUqqNDIny4QTLlYCwAQ#q=pakistan"/*new BasicDAO().getNonProcessedLink()*/)); 
                             System.out.println("resume with saved link true");


                        thread.start();

                        System.out.println("thread stared");
                        threadList.add(thread);
                        System.out.println("thread added to arraylist");

                    } catch (Exception ex) {
                        new Logging().logError(ex.toString());
                    }

               }

调试:

for 11 threads , its says in logs:

queue loaded, new  size ------------------------------------ 1000
This is inside of sync block.   -----------    queue size 1000
This is at the end of sync block.   -----------    queue size 1000
queue size 0
queue loaded, new  size ------------------------------------ 1000
This is inside of sync block.   -----------    queue size 1000
queue size 0
This is at the end of sync block.   -----------    queue size 1000
queue loaded, new  size ------------------------------------ 1000
This is inside of sync block.   -----------    queue size 1000
This is at the end of sync block.   -----------    queue size 1000
queue size 0
queue loaded, new  size ------------------------------------ 1000
This is inside of sync block.   -----------    queue size 1000
This is at the end of sync block.   -----------    queue size 1000
queue size 0
queue loaded, new  size ------------------------------------ 1000
This is inside of sync block.   -----------    queue size 1000
This is at the end of sync block.   -----------    queue size 1000
queue size 0
queue loaded, new  size ------------------------------------ 1000
This is inside of sync block.   -----------    queue size 1000
This is at the end of sync block.   -----------    queue size 1000
queue size 0
queue loaded, new  size ------------------------------------ 1000
This is inside of sync block.   -----------    queue size 1000
This is at the end of sync block.   -----------    queue size 1000
queue size 0
queue loaded, new  size ------------------------------------ 1000
This is inside of sync block.   -----------    queue size 1000
This is at the end of sync block.   -----------    queue size 1000
queue size 0
queue loaded, new  size ------------------------------------ 1000
This is inside of sync block.   -----------    queue size 1000
This is at the end of sync block.   -----------    queue size 1000
queue size 0
queue loaded, new  size ------------------------------------ 1000
This is inside of sync block.   -----------    queue size 1000
This is at the end of sync block.   -----------    queue size 1000
queue size 0
queue loaded, new  size ------------------------------------ 1000
This is inside of sync block.   -----------    queue size 1000
This is at the end of sync block.   -----------    queue size 1000
Just worked on --------- http://ao.com/Advice/Washing-Machines/Top-Tens/Top-Five-Washing-Machines/Advice/Freezers/Top-Tens/Top-Five-Freezers/flavel
queue size 999
Just worked on --------- http://ao.com/Advice/Washing-Machines/Top-Tens/Top-Five-Washing-Machines/l/fridges-width_less_than_50_cm/1-26/29-30//zanussi
queue loaded, new  size ------------------------------------ 1999
This is inside of sync block.   -----------    queue size 1999
This is at the end of sync block.   -----------    queue size 1999
queue size 999
queue loaded, new  size ------------------------------------ 1999
This is inside of sync block.   -----------    queue size 1999
This is at the end of sync block.   -----------    queue size 1999
Just worked on --------- http://ao.com/Advice/Washing-Machines/Top-Tens/Top-Five-Washing-Machines/Advice/Refrigerators/Top-Tens/Top-Five-Fridges/l/small_appliances-bodum/1-6/55/
queue size 999
queue loaded, new  size ------------------------------------ 1999
This is inside of sync block.   -----------    queue size 1999
This is at the end of sync block.   -----------    queue size 1999
8692 characters / 254 lines
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Answer 1

由于这一行，代码将不会按预期运行: 同步(Crawler.class)您已经锁定了 Crawler 的“类”对象，每个类加载器一个，但是您的同步方法是非静态的。用静态同步方法替换非静态同步方法，应该可以解决问题。