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copied!<p>The one flaw in that approach is that the "real" time <code>doSomething()</code> takes to execute can vary wildly depending on what other programs are running on the system and what its load is. This makes the performance measurement somewhat imprecise.</p> <p>One more accurate way of tracking the time it takes to execute code, assuming the code is single-threaded, is to look at the CPU time consumed by the thread during the call. You can do this with the JMX classes; in particular, with <a href="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/management/ThreadMXBean.html" rel="nofollow noreferrer"><code>ThreadMXBean</code></a>. You can retrieve an instance of <code>ThreadMXBean</code> from <a href="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/management/ManagementFactory.html" rel="nofollow noreferrer"><code>java.lang.management.ManagementFactory</code></a>, and, if your platform supports it (most do), use the <a href="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/management/ThreadMXBean.html#getCurrentThreadCpuTime()" rel="nofollow noreferrer"><code>getCurrentThreadCpuTime</code></a> method in place of <code>System.currentTimeMillis</code> to do a similar test. Bear in mind that <code>getCurrentThreadCpuTime</code> reports time in nanoseconds, not milliseconds.</p> <p>Here's a sample (Scala) method that could be used to perform a measurement:</p> <pre><code>def measureCpuTime(f: => Unit): java.time.Duration = { import java.lang.management.ManagementFactory.getThreadMXBean if (!getThreadMXBean.isThreadCpuTimeSupported) throw new UnsupportedOperationException( "JVM does not support measuring thread CPU-time") var finalCpuTime: Option[Long] = None val thread = new Thread { override def run(): Unit = { f finalCpuTime = Some(getThreadMXBean.getThreadCpuTime( Thread.currentThread.getId)) } } thread.start() while (finalCpuTime.isEmpty && thread.isAlive) { Thread.sleep(100) } java.time.Duration.ofNanos(finalCpuTime.getOrElse { throw new Exception("Operation never returned, and the thread is dead " + "(perhaps an unhandled exception occurred)") }) } </code></pre> <p>(Feel free to translate the above to Java!)</p> <p>This strategy isn't perfect, but it's less subject to variations in system load.</p>

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