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Eamonn McManus's BlogA helper class for performance statisticsPosted by emcmanus on November 23, 2006 at 03:31 AM | Comments (4)I recently wanted to add some performance measurements to an application. To avoid duplicating code everywhere I needed to make measurements, I coded up a small helper class. What I wanted to measure was the amount of time taken by various operations within the application. For each operation, I wanted to know various statistics about it: how many times it was called, the average time it took, and also the minimum, maximum, and standard deviation. The basic skeleton for timing code is this:
long startTime = System.nanoTime();
doTheOperation();
long elapsedTime = System.nanoTime() - startTime;
The System.nanoTime() method was introduced in the J2SE 5.0 release. Its intended use is exactly for timing measurements such as this. As the name implies, the result is in nanoseconds, though it will not usually be accurate to the nearest nanosecond. If we want to accumulate statistics about
long startTime = System.nanoTime();
doTheOperation();
long elapsedTime = System.nanoTime() - startTime;
synchronized (something) {
nCalls++;
sumTime += elapsedTime;
minTime = Math.min(minTime, elapsedTime);
maxTime = Math.max(maxTime, elapsedTime);
}
Not only does this pollute the
public class ClassContainingTheOperationToBeMeasured {
private final CallStats operationStats = new CallStats();
...
CallStats.Call call = operationStats.newCall();
doTheOperation();
call.end();
...
}
For each collection of timing statistics, we'll need an instance
of So here's the class I coded for this:
import java.beans.ConstructorProperties;
import java.io.Serializable;
public class CallStats implements Serializable {
private int nCalls;
private long minTime;
private long maxTime;
private long sumTime;
private double sumSquaredTime;
/** Creates a new instance of CallStats */
public CallStats() {
}
@ConstructorProperties({"nCalls", "minTime", "maxTime", "sumTime",
"sumSquaredTime"})
public CallStats(int nCalls, long minTime, long maxTime, long sumTime,
double sumSquaredTime) {
this.nCalls = nCalls;
this.minTime = minTime;
this.maxTime = maxTime;
this.sumTime = sumTime;
this.sumSquaredTime = sumSquaredTime;
}
public int getNCalls() {
return nCalls;
}
public long getMinTime() {
return Math.max(0, minTime);
}
public long getMaxTime() {
return maxTime;
}
public long getSumTime() {
return sumTime;
}
public double getSumSquaredTime() {
return sumSquaredTime;
}
public long getMeanTime() {
if (nCalls == 0)
return 0;
else
return sumTime / nCalls;
}
public long getStdDevTime() {
if (nCalls == 0)
return 0;
double mean = getMeanTime();
double meanSquared = mean * mean;
double meanOfSquares = sumSquaredTime / nCalls;
double variance = meanOfSquares - meanSquared;
if (variance < 0)
return 0; // might happen due to rounding error
return (long) Math.sqrt(variance);
}
public String toString() {
return "nCalls = " + nCalls + ";\n" +
"sumTime = " + getSumTime() + ";\n" +
"minTime = " + minTime + ";\n" +
"maxTime = " + maxTime + ";\n" +
"meanTime = " + getMeanTime() + ";\n" +
"stdDevTime = " + getStdDevTime();
}
public Call newCall() {
return new Call();
}
public class Call {
private final long startTime = System.nanoTime();
private Call() {}
public void end() {
long elapsed = System.nanoTime() - startTime;
synchronized (CallStats.this) {
nCalls++;
if (elapsed < minTime || nCalls == 1)
minTime = elapsed;
if (elapsed > maxTime)
maxTime = elapsed;
sumTime += elapsed;
double elapsedFP = elapsed;
sumSquaredTime += elapsedFP * elapsedFP;
}
}
}
}
A few remarks are in order. First, the
public interface MeasurementMXBean {
public CallStats getFooStats();
public CallStats getBarStats();
}
The presence of the
MeasurementMXBean proxy =
JMX.newMXBeanProxy(mbeanServer, name, MeasureMXBean.class);
CallStats stats = proxy.getFooStats();
Second, there are a lot of nanoseconds in a second. So we
have to be on the lookout for overflow. A Finally, you might have noticed an asymmetry between the
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