nGrinder源码分析：自动中断测试任务

1.背景

在运行nGrinder任务时，会出现任务被系统中断，为什么会自动中断呢？是bug还是一种保护机制？本文通过源码分析的方式来解读。

2.源码分析

之前的一篇文章:性能测试工具 nGrinder 项目剖析及二次开发，介绍了nGrinder的整体架构，知道ngrinder-core/src/main/java/net/grinder/SingleConsole.java是将测试脚本发布到Agent并在其上执行性能测试，该类实现了收集测试过程中的采样数据，将数据分成两部分记录：

1. 写入记录文件，供时序图展示（*.data和csv)
2. 写入内存，供详细数据展示（private Map<String, Object> statisticData, 持久化到DB）

其中将采样数据写到第一部分（*.data和csv）的实现方法如下：

/*     * (non-Javadoc)     *     * @see     * net.grinder.console.model.SampleListener#update(net.grinder.statistics     * .StatisticsSet, net.grinder.statistics.StatisticsSet)     */    @Override    public void update(final StatisticsSet intervalStatistics,            final StatisticsSet cumulativeStatistics) {        try {            if (!capture) {                return;            }            samplingCount++;            long currentPeriod = cumulativeStatistics.getValue(getSampleModel()                    .getPeriodIndex());            setTpsValue(sampleModel.getTPSExpression().getDoubleValue(                    intervalStatistics));            checkTooLowTps(getTpsValues());            updateStatistics(intervalStatistics, cumulativeStatistics);            // 将采样数据写入csv数据            // hugang            writeIntervalCsvData(intervalStatistics);            int interval = getSampleModel().getSampleInterval();            long gap = 1;            if (samplingCount == 1) {                lastSamplingPeriod = currentPeriod;            } else {                lastSamplingPeriod = lastSamplingPeriod + interval;                gap = ((currentPeriod - lastSamplingPeriod) / interval);            }            // Adjust sampling delay.. run write data multiple times... when it            // takes longer than 1            // sec.            samplingLifeCycleListener                    .apply(new Informer<SamplingLifeCycleListener>() {                        @Override                        public void inform(SamplingLifeCycleListener listener) {                            listener.onSampling(getReportPath(),                                    intervalStatistics, cumulativeStatistics);                        }                    });            for (int i = 0; i < (gap + 1); i++) {                final boolean lastCall = (samplingCount == 1 && i == 0)                        || (samplingCount != 1 && i == gap);                // 将采样数据写到*.data文件                // hugang                writeIntervalSummaryData(intervalStatistics, lastCall);                if (interval >= (MIN_SAMPLING_INTERVAL_TO_ACTIVATE_TPS_PER_TEST)) {                    writeIntervalSummaryDataPerTest(                            intervalStatisticMapPerTest, lastCall);                }                samplingLifeCycleFollowupListener                        .apply(new Informer<SamplingLifeCycleFollowUpListener>() {                            @Override                            public void inform(                                    SamplingLifeCycleFollowUpListener listener) {                                listener.onSampling(getReportPath(),                                        intervalStatistics,                                        cumulativeStatistics, lastCall);                            }                        });            }            checkTooManyError(cumulativeStatistics);            lastSamplingPeriod = lastSamplingPeriod + (interval * gap);        } catch (RuntimeException e) {            LOGGER.error("Error occurred while updating the statistics : {}",                    e.getMessage());            LOGGER.debug("Details : ", e);            throw e;        }    }

其中：

writeIntervalCsvData(intervalStatistics);writeIntervalSummaryData(intervalStatistics, lastCall);

分别将采样数据写到output.csv和*.data。

注意，有2个check方法：

checkTooLowTps(getTpsValues());checkTooManyError(cumulativeStatistics);

checkTooLowTps(getTpsValues());会判断1分钟内TPS小于0.01，如果为true，将向ConsoleShutdownListener监听器发送停止信号。

/**     * Check if the TPS is too low. the TPS is lower than 0.001 for 1 minutes,     * It emits a shutdown event to the {@link ConsoleShutdownListener}     *     * @param tps     *            current TPS     */    private void checkTooLowTps(double tps) {        // If the tps is too low, which means the agents or scripts went wrong.        if (tps < 0.001) {            if (momentWhenTpsBeganToHaveVerySmall == 0) {                momentWhenTpsBeganToHaveVerySmall = System.currentTimeMillis();            } else if (new Date().getTime() - momentWhenTpsBeganToHaveVerySmall >= TOO_LOW_TPS_TIME) {                LOGGER.warn(                        "Stop the test because its tps is less than 0.001 for more than {} minitue.",                        TOO_LOW_TPS_TIME / 60000);                getListeners().apply(new Informer<ConsoleShutdownListener>() {                    public void inform(ConsoleShutdownListener listener) {                        listener.readyToStop(StopReason.TOO_LOW_TPS);                    }                });                momentWhenTpsBeganToHaveVerySmall = 0;            }        } else {            momentWhenTpsBeganToHaveVerySmall = 0;        }    }

private void checkTooManyError(StatisticsSet cumulativeStatistics):会判断10s内事务数错误率>=50%，如果为true，通知监听器ConsoleShutdownListener listener终止任务。

/**     * Check if too many error has been occurred. If the half of total     * transaction is error for the last 10 secs. It notifies the     * {@link ConsoleShutdownListener}     *     * @param cumulativeStatistics     *            accumulated Statistics     */    private void checkTooManyError(StatisticsSet cumulativeStatistics) {        StatisticsIndexMap statisticsIndexMap = getStatisticsIndexMap();        long testSum = cumulativeStatistics.getCount(statisticsIndexMap                .getLongSampleIndex("timedTests"));        long errors = cumulativeStatistics.getValue(statisticsIndexMap                .getLongIndex("errors"));        // testSum 成功事务数， errors 失败事务数        // hugang        if (((double) (testSum + errors)) / 2 < errors) {            if (lastMomentWhenErrorsMoreThanHalfOfTotalTPSValue == 0) {                lastMomentWhenErrorsMoreThanHalfOfTotalTPSValue = System                        .currentTimeMillis();            } else if (isOverLowTpsThreshold()) {                LOGGER.warn(                        "Stop the test because the count of test error is more than"                                + " half of total tps for last {} seconds.",                        TOO_MANY_ERROR_TIME / 1000);                getListeners().apply(new Informer<ConsoleShutdownListener>() {                    public void inform(ConsoleShutdownListener listener) {                        listener.readyToStop(StopReason.TOO_MANY_ERRORS);                    }                });                lastMomentWhenErrorsMoreThanHalfOfTotalTPSValue = 0;            }        }    }

3.总结

nGrinder中断测试任务，是一种保护机制，当被测系统性能已经很差，nGrinder不会继续对该系统产生压力。

判断标准：

1. TPS在1分钟内小于0.001
2. 事务错误率在10s内大于等于50%

如果上述条件，某一条为true，自动中断任务。

附：
nGrinder的debug日志为：
/root/.ngrinder/logs/ngrinder.log