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：

写入记录文件，供时序图展示（*.data和csv)

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：

TPS在1分钟内小于0.001

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