Programming with JMeter-- JMeterThread

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JMeter

JMeterThread ThreadGroup

到上一篇ThreadGroup为止，基本上在项目中可以完成对JMeterEngine / ThreadGroup 的整合，现在要来分析下JMeterThread，以便更好的集成到项目中。

一个 JMeterThread 好比一个vu（虚拟用户），他的创建和启动已经在ThreadGroup这一篇中完整的分析，我们是将JMeterThread委托给一个叫做DaemonizableNamedRunnable（这是因为我需要整合 weblogic workmanager 统一管理线程池）的实例来运行的，附DaemonizableNamedRunnable代码

//remote case
runnable = new DaemonizableNamedRunnable() {

						@Override
						public String getName()
						{
							return jmThread.getThreadName();
						}

						@Override
						public boolean isDaemon()
						{
							return true;
						}

						@Override
						public void release()
						{
						}

						@Override
						public void run()
						{
							Security.runAs(subj, new PrivilegedAction<Void>() {

								@Override
								public Void run()
								{
									jmThread.run();
									return null;
								}
							});
						}
					};

//Local Case
runnable = new DaemonizableNamedRunnable() {

						@Override
						public String getName()
						{
							return jmThread.getThreadName();
						}

						@Override
						public boolean isDaemon()
						{
							return true;
						}

						@Override
						public void release()
						{
						}

						@Override
						public void run()
						{
							jmThread.run();
						}
					};

也就是说外围的一些工作都在ThreadGroup里完成了，现在看看其内部的结构，首先看下大概的类图(不全，JMeterEngine没有画进去)：

结合初始化创建代码：

//ThreadGroup创建JMeterThread
private CustomJMeterThread makeThread(int groupCount, ListenerNotifier notifier, ListedHashTree threadGroupTree,
			StandardJMeterEngine engine, int i, JMeterContext context)
	{ // N.B. Context needs to be fetched in the correct thread
		boolean onErrorStopTest = getOnErrorStopTest();
		boolean onErrorStopTestNow = getOnErrorStopTestNow();
		boolean onErrorStopThread = getOnErrorStopThread();
		boolean onErrorStartNextLoop = getOnErrorStartNextLoop();
		String groupName = getName();
		final CustomJMeterThread jmeterThread = new CustomJMeterThread(cloneTree(threadGroupTree), this, notifier);
		jmeterThread.setThreadNum(i);
		jmeterThread.setThreadGroup(this);//持有线程所属的 ThreadGroup 实例
		jmeterThread.setInitialContext(context);
		final String threadName = groupName + " " + groupCount + "-" + (i + 1);
		jmeterThread.setThreadName(threadName);
		jmeterThread.setEngine(engine); //持有一个 当前运行的 JMeterEngine 实例，这个以后会有用
		jmeterThread.setOnErrorStopTest(onErrorStopTest);
		jmeterThread.setOnErrorStopTestNow(onErrorStopTestNow);
		jmeterThread.setOnErrorStopThread(onErrorStopThread);
		jmeterThread.setOnErrorStartNextLoop(onErrorStartNextLoop);
		return jmeterThread;
	}

//JMeterThread 构造方法
public JMeterThread(HashTree test, JMeterThreadMonitor monitor, ListenerNotifier note) {
        this.monitor = monitor;
        threadVars = new JMeterVariables();
        testTree = test;
        compiler = new TestCompiler(testTree);
        controller = (Controller) testTree.getArray()[0];
        SearchByClass<TestIterationListener> threadListenerSearcher = new SearchByClass<TestIterationListener>(TestIterationListener.class); // TL - IS
        test.traverse(threadListenerSearcher);
        testIterationStartListeners = threadListenerSearcher.getSearchResults();
        notifier = note;
        running = true;
    }

//JMeterThread保存线程上下文变量
public void setInitialContext(JMeterContext context) {
        threadVars.putAll(context.getVariables());
    }

非常清晰了，JMeterThread的创建和初始化基本上针对以下几点：

1） onError 设置，方便在出错时响应

2）设置线程所在的ThreadGroup 和 JMeterEngine

3）保存好上下文到线程 Local 的 JMeterVariables

4）保存好测试数据结构 HashTree, 解析出controller, listener. 之前我们提到过JMeter 提供了注入 LoopController / Runtime 来控制线程的循环，和注入ResultCollector之类的Listener来收集测试结果。

初始化完毕，我们再来看运行过程，即run()方法：

 @Override
    public void run() {
        // threadContext is not thread-safe, so keep within thread
        JMeterContext threadContext = JMeterContextService.getContext();
        LoopIterationListener iterationListener=null;

        try {
            iterationListener = initRun(threadContext);
            while (running) {
                Sampler sam = controller.next();
                while (running && sam != null) {
                	process_sampler(sam, null, threadContext);
                	threadContext.cleanAfterSample();
                	if(onErrorStartNextLoop || threadContext.isRestartNextLoop()) {
                	    if(threadContext.isRestartNextLoop()) {
                            triggerEndOfLoopOnParentControllers(sam, threadContext);
                            sam = null;
                            threadContext.getVariables().put(LAST_SAMPLE_OK, TRUE);
                            threadContext.setRestartNextLoop(false);
                	    } else {
                    		boolean lastSampleFailed = !TRUE.equals(threadContext.getVariables().get(LAST_SAMPLE_OK));
                    		if(lastSampleFailed) {
    	                		if(log.isDebugEnabled()) {
    	                    		log.debug("StartNextLoop option is on, Last sample failed, starting next loop");
    	                    	}
    	                    	triggerEndOfLoopOnParentControllers(sam, threadContext);
    	                        sam = null;
    	                        threadContext.getVariables().put(LAST_SAMPLE_OK, TRUE);
                    		} else {
                    			sam = controller.next();
                    		}
                	    }
                	} 
                	else {
                		sam = controller.next();
                	}
                }
                if (controller.isDone()) {
                    running = false;
                }
            }
        }
        // Might be found by contoller.next()
        catch (JMeterStopTestException e) {
            log.info("Stopping Test: " + e.toString());
            stopTest();
        }
        catch (JMeterStopTestNowException e) {
            log.info("Stopping Test Now: " + e.toString());
            stopTestNow();
        } catch (JMeterStopThreadException e) {
            log.info("Stop Thread seen: " + e.toString());
        } catch (Exception e) {
            log.error("Test failed!", e);
        } catch (ThreadDeath e) {
            throw e; // Must not ignore this one
        } catch (Error e) {// Make sure errors are output to the log file
            log.error("Test failed!", e);
        } finally {
            currentSampler = null; // prevent any further interrupts
            try {
                interruptLock.lock();  // make sure current interrupt is finished, prevent another starting yet
                threadContext.clear();
                log.info("Thread finished: " + threadName);
                threadFinished(iterationListener);
                monitor.threadFinished(this); // Tell the monitor we are done
                JMeterContextService.removeContext(); // Remove the ThreadLocal entry
            }
            finally {
                interruptLock.unlock(); // Allow any pending interrupt to complete (OK because currentSampler == null)
            }
        }
    }

代码结构很清晰：

1) initRun(代码省略):

初始化Thread Context （主要是初始化好当前 Thread / threadgroup / engine 实例，线程上下文变量，线程数，线程循环控制器，监听器），

执行线程正式运行前的delay（若有thread rampup 策略的话）工作

Thread计数，numberOfActiveThreads / numberOfThreadsStarted / numberOfThreads

2）循环运行，直到 running 为 false（一般manually 停止测试就必须会设置该flag为false） OR controller.next()为null，也就是说配置的循环控制器执行完毕

3）finally 清理线程：这里有行比较重要的代码 “monitor.threadFinished(this);” ，这个monitor是什么呢？往下看。（Q1）

中间循环运行比较复杂的是process_sampler(sam, null, threadContext); 这个方法会真正触发客户端的测试代码的地方，代码很长就略去了，核心的逻辑大概如下：

1）分析Sampler是否是TransactionSampler, 若是解析Transaction 范围的一组Sampler Pack 进行递归process

2）Sampler.sample(Entry e)方法，产生一个SampleResult

3）把result包装成一个SampleEvent 并通知所有的监听器

所有的 SampleListener #sampleOccur 方法被触发， ResultCollector 就会有相应的措施来保存测试结果。

附接口 Sampler（主要有JavaSampler / TransationSampler / BeanShellSampler 等）， SampleListener （最终要的是ResultCollector,另外还有ResultAction,Summariser等）代码：

public interface Sampler extends Serializable, TestElement {
    /**
     * Obtains statistics about the given Entry, and packages the information
     * into a SampleResult.
     */
    SampleResult sample(Entry e);
}

public interface SampleListener {
    /**
     * A sample has started and stopped.
     */
    void sampleOccurred(SampleEvent e);

    /**
     * A sample has started.
     */
    void sampleStarted(SampleEvent e);

    /**
     * A sample has stopped.
     */
    void sampleStopped(SampleEvent e);
}

留下问题Q1： “monitor.threadFinished(this);” ，这个monitor是什么呢？

这个monitor其实就当前Thread 所在的 ThreadGroup，这里相当与对ThreadGroup的一个回调，如果有些资源清理必须在同一个线程中做的话就会很有用，比如一个case，我的测试代码中需要一个JNDI Context 进行lookup，那么这个JNDI Context 的close工作应该是在创建他的同一个线程中去做，那么线程结束的时候去清理是最好不过了，所以可以重写ThreadGroup的threadFinished（JMeterThread）方法：

@Override
	public void threadFinished(JMeterThread thread)
	{
		super.threadFinished(thread);
		Context ctx = (Context) (thread instanceof ITestResourceHolder ? ((ITestResourceHolder) thread).getResourceMap().get(
				JMeterTestResource.JNDI_CONTEXT) : null);
		if (ctx != null) {
			try {
				log.debug("Thread " + Thread.currentThread().getName() + " closing InitialContext " + ctx);
				ctx.close();
			}
			catch (NamingException e) {
				log.error("Exception occurred when try to close the InitialContext ", e);
			}
			finally {
				((ITestResourceHolder) thread).getResourceMap().clear();
			}
		}
	}

和JMeterEngine一样，我在扩展JMeterThread时顺便实现了ITestResourceHolder接口用来维护额外的线程变量（比如JNDIContext）.