今天有兴趣重新看了一下heritrix3.1.0系统里面的线程池源码，heritrix系统没有采用java的cocurrency包里面的并发框架，而是采用了线程组ThreadGroup类来实现线程池的（线程组类似于树结构，一个线程组包含多个子线程组或多个子线程，数据结构类似于composite模式，不过枝节点与叶子节点没有实现类似composite模式的共同接口）
关键类是org.archive.crawler.framework包里面的ToePool类与ToeThread类，前者继承自ThreadGroup类,后者继承自Thread类
ToeThread显然是工作线程，用于执行采集任务，构造函数初始化成员变量CrawlController controller，用于获取Frontier对象及相关处理器链
private CrawlController controller; private String coreName; private CrawlURI currentCuri; /** * Create a ToeThread * * @param g ToeThreadGroup * @param sn serial number */ public ToeThread(ToePool g, int sn) { // TODO: add crawl name? super(g,"ToeThread #" + sn); coreName="ToeThread #" + sn + ": "; controller = g.getController(); serialNumber = sn; setPriority(DEFAULT_PRIORITY); int outBufferSize = controller.getRecorderOutBufferBytes(); int inBufferSize = controller.getRecorderInBufferBytes(); httpRecorder = new Recorder(controller.getScratchDir().getFile(), "tt" + sn + "http", outBufferSize, inBufferSize); lastFinishTime = System.currentTimeMillis(); } /** (non-Javadoc) * @see java.lang.Thread#run() */ public void run() { String name = controller.getMetadata().getJobName(); logger.fine(getName()+" started for order '"+name+"'"); Recorder.setHttpRecorder(httpRecorder); try { while ( true ) { ArchiveUtils.continueCheck(); setStep(Step.ABOUT_TO_GET_URI, null); CrawlURI curi = controller.getFrontier().next(); synchronized(this) { ArchiveUtils.continueCheck(); setCurrentCuri(curi); currentCuri.setThreadNumber(this.serialNumber); lastStartTime = System.currentTimeMillis(); currentCuri.setRecorder(httpRecorder); } try { KeyedProperties.loadOverridesFrom(curi); controller.getFetchChain().process(curi,this); controller.getFrontier().beginDisposition(curi); controller.getDispositionChain().process(curi,this); } catch (RuntimeExceptionWrapper e) { // Workaround to get cause from BDB if(e.getCause() == null) { e.initCause(e.getCause()); } recoverableProblem(e); } catch (AssertionError ae) { // This risks leaving crawl in fatally inconsistent state, // but is often reasonable for per-Processor assertion problems recoverableProblem(ae); } catch (RuntimeException e) { recoverableProblem(e); } catch (InterruptedException e) { if(currentCuri!=null) { recoverableProblem(e); Thread.interrupted(); // clear interrupt status } else { throw e; } } catch (StackOverflowError err) { recoverableProblem(err); } catch (Error err) { // OutOfMemory and any others seriousError(err); } finally { httpRecorder.endReplays(); KeyedProperties.clearOverridesFrom(curi); } setStep(Step.ABOUT_TO_RETURN_URI, null); ArchiveUtils.continueCheck(); synchronized(this) { controller.getFrontier().finished(currentCuri); controller.getFrontier().endDisposition(); setCurrentCuri(null); } curi = null; setStep(Step.FINISHING_PROCESS, null); lastFinishTime = System.currentTimeMillis(); if(shouldRetire) { break; // from while(true) } } } catch (InterruptedException e) { if(currentCuri!=null){ logger.log(Level.SEVERE,"Interrupt leaving unfinished CrawlURI "+getName()+" - job may hang",e); } // thread interrupted, ok to end logger.log(Level.FINE,this.getName()+ " ended with Interruption"); } catch (Exception e) { // everything else (including interruption) logger.log(Level.SEVERE,"Fatal exception in "+getName(),e); } catch (OutOfMemoryError err) { seriousError(err); } finally { controller.getFrontier().endDisposition(); } setCurrentCuri(null); // Do cleanup so that objects can be GC. this.httpRecorder.closeRecorders(); this.httpRecorder = null; logger.fine(getName()+" finished for order '"+name+"'"); setStep(Step.FINISHED, null); controller = null; } ToePool是线程组，用于管理上面的工作线程，初始化、查看活动线程、中断或终止工作线程等
protected CrawlController controller; protected int nextSerialNumber = 1; protected int targetSize = 0; /** * Constructor. Creates a pool of ToeThreads. * * @param c A reference to the CrawlController for the current crawl. */ public ToePool(AlertThreadGroup atg, CrawlController c) { //传入父线程组 super(atg, "ToeThreads"); this.controller = c; setDaemon(true); } public void cleanup() { // force all Toes waiting on queues, etc to proceed Thread[] toes = getToes(); for(Thread toe : toes) { if(toe!=null) { toe.interrupt(); } }// this.controller = null; } /** * @return The number of ToeThreads that are not available (Approximation). */ public int getActiveToeCount() { Thread[] toes = getToes(); int count = 0; for (int i = 0; i < toes.length; i++) { if((toes[i] instanceof ToeThread) && ((ToeThread)toes[i]).isActive()) { count++; } } return count; } /** * @return The number of ToeThreads. This may include killed ToeThreads * that were not replaced. */ public int getToeCount() { Thread[] toes = getToes(); int count = 0; for (int i = 0; i 0) { // must create threads for(int i = 1; i <= difference; i++) { //启动线程 startNewThread(); } } else { //退出多余线程 // must retire extra threads int retainedToes = targetSize; Thread[] toes = this.getToes(); for (int i = 0; i < toes.length ; i++) { if(!(toes[i] instanceof ToeThread)) { continue; } retainedToes--; if (retainedToes>=0) { continue; // this toe is spared } // otherwise: ToeThread tt = (ToeThread)toes[i]; tt.retire(); } } } /** * Kills specified thread. Killed thread can be optionally replaced with a * new thread. * * WARNING: This operation should be used with great care. It may * destabilize the crawler. * * @param threadNumber Thread to kill * @param replace If true then a new thread will be created to take the * killed threads place. Otherwise the total number of threads * will decrease by one. */ public void killThread(int threadNumber, boolean replace){ Thread[] toes = getToes(); for (int i = 0; i< toes.length; i++) { if(! (toes[i] instanceof ToeThread)) { continue; } ToeThread toe = (ToeThread) toes[i]; if(toe.getSerialNumber()==threadNumber) { toe.kill(); } } if(replace){ // Create a new toe thread to take its place. Replace toe startNewThread(); } } //锁定，防止并发初始化线程 private synchronized void startNewThread() { ToeThread newThread = new ToeThread(this, nextSerialNumber++); newThread.setPriority(DEFAULT_TOE_PRIORITY); newThread.start(); }public void waitForAll() { while (true) try { if (isAllAlive(getToes())) { return; } Thread.sleep(1000); } catch (InterruptedException e) { throw new IllegalStateException(e); } } private static boolean isAllAlive(Thread[] threads) { for (Thread t: threads) { if ((t != null) && (!t.isAlive())) { return false; } } return true; }
最后，线程组的初始化及工作线程的相关管理在CrawlController对象的相关方法执行
/** * Maximum number of threads processing URIs at the same time. */ int maxToeThreads; public int getMaxToeThreads() { return maxToeThreads; } @Value("25") public void setMaxToeThreads(int maxToeThreads) { this.maxToeThreads = maxToeThreads; if(toePool!=null) { toePool.setSize(this.maxToeThreads); } }private transient ToePool toePool;/** * Called when the last toethread exits. */ protected void completeStop() { LOGGER.fine("Entered complete stop."); statisticsTracker.getSnapshot(); // ??? this.reserveMemory = null; if (this.toePool != null) { this.toePool.cleanup(); } this.toePool = null; LOGGER.fine("Finished crawl."); try { appCtx.stop(); } catch (RuntimeException re) { LOGGER.log(Level.SEVERE,re.getMessage(),re); } sendCrawlStateChangeEvent(State.FINISHED, this.sExit); // CrawlJob needs to be sure all beans have received FINISHED signal before teardown this.isStopComplete = true; appCtx.publishEvent(new StopCompleteEvent(this)); }/** * Operator requested for crawl to stop. */ public synchronized void requestCrawlStop() { if(state == State.STOPPING) { // second stop request; nudge the threads with interrupts getToePool().cleanup(); } requestCrawlStop(CrawlStatus.ABORTED); }/** * @return Active toe thread count. */ public int getActiveToeCount() { if (toePool == null) { return 0; } return toePool.getActiveToeCount(); } protected void setupToePool() { toePool = new ToePool(alertThreadGroup,this); // TODO: make # of toes self-optimizing toePool.setSize(getMaxToeThreads()); toePool.waitForAll(); } /** * @return The number of ToeThreads * * @see ToePool#getToeCount() */ public int getToeCount() { return this.toePool == null? 0: this.toePool.getToeCount(); } /** * @return The ToePool */ public ToePool getToePool() { return toePool; } /** * Kills a thread. For details see * { @link org.archive.crawler.framework.ToePool#killThread(int, boolean) * ToePool.killThread(int, boolean)}. * @param threadNumber Thread to kill. * @param replace Should thread be replaced. * @see org.archive.crawler.framework.ToePool#killThread(int, boolean) */ public void killThread(int threadNumber, boolean replace){ toePool.killThread(threadNumber, replace); } 说得够清楚吧
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本系列Heritrix 3.1.0 源码解析系本人原创
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