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/*
* Copyright (C) 2009, Christian Halstrick <christian.halstrick@sap.com> and others
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Distribution License v. 1.0 which is available at
* https://www.eclipse.org/org/documents/edl-v10.php.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
package org.eclipse.jgit.util;
import java.lang.management.ManagementFactory;
import java.lang.management.ThreadMXBean;
/**
* A simple stopwatch which measures elapsed CPU time of the current thread. CPU
* time is the time spent on executing your own code plus the time spent on
* executing operating system calls triggered by your application.
* <p>
* This stopwatch needs a VM which supports getting CPU Time information for the
* current thread. The static method createInstance() will take care to return
* only a new instance of this class if the VM is capable of returning CPU time.
*/
public class CPUTimeStopWatch {
private long start;
private static ThreadMXBean mxBean=ManagementFactory.getThreadMXBean();
/**
* use this method instead of the constructor to be sure that the underlying
* VM provides all features needed by this class.
*
* @return a new instance of {@link #CPUTimeStopWatch()} or
* <code>null</code> if the VM does not support getting CPU time
* information
*/
public static CPUTimeStopWatch createInstance() {
return mxBean.isCurrentThreadCpuTimeSupported() ? new CPUTimeStopWatch()
: null;
}
/**
* Starts the stopwatch. If the stopwatch is already started this will
* restart the stopwatch.
*/
public void start() {
start = mxBean.getCurrentThreadCpuTime();
}
/**
* Stops the stopwatch and return the elapsed CPU time in nanoseconds.
* Should be called only on started stopwatches.
*
* @return the elapsed CPU time in nanoseconds. When called on non-started
* stopwatches (either because {@link #start()} was never called or
* {@link #stop()} was called after the last call to
* {@link #start()}) this method will return 0.
*/
public long stop() {
long cpuTime = readout();
start = 0;
return cpuTime;
}
/**
* Return the elapsed CPU time in nanoseconds. In contrast to
* {@link #stop()} the stopwatch will continue to run after this call.
*
* @return the elapsed CPU time in nanoseconds. When called on non-started
* stopwatches (either because {@link #start()} was never called or
* {@link #stop()} was called after the last call to
* {@link #start()}) this method will return 0.
*/
public long readout() {
return (start == 0) ? 0 : mxBean.getCurrentThreadCpuTime() - start;
}
}
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