1 /*
2 * Copyright (C) 2009, Christian Halstrick <christian.halstrick@sap.com> and others
3 *
4 * This program and the accompanying materials are made available under the
5 * terms of the Eclipse Distribution License v. 1.0 which is available at
6 * https://www.eclipse.org/org/documents/edl-v10.php.
7 *
8 * SPDX-License-Identifier: BSD-3-Clause
9 */
10
11 package org.eclipse.jgit.util;
12
13 import java.lang.management.ManagementFactory;
14 import java.lang.management.ThreadMXBean;
15
16 /**
17 * A simple stopwatch which measures elapsed CPU time of the current thread. CPU
18 * time is the time spent on executing your own code plus the time spent on
19 * executing operating system calls triggered by your application.
20 * <p>
21 * This stopwatch needs a VM which supports getting CPU Time information for the
22 * current thread. The static method createInstance() will take care to return
23 * only a new instance of this class if the VM is capable of returning CPU time.
24 */
25 public class CPUTimeStopWatch {
26 private long start;
27
28 private static ThreadMXBean mxBean=ManagementFactory.getThreadMXBean();
29
30 /**
31 * use this method instead of the constructor to be sure that the underlying
32 * VM provides all features needed by this class.
33 *
34 * @return a new instance of {@link #CPUTimeStopWatch()} or
35 * <code>null</code> if the VM does not support getting CPU time
36 * information
37 */
38 public static CPUTimeStopWatch createInstance() {
39 return mxBean.isCurrentThreadCpuTimeSupported() ? new CPUTimeStopWatch()
40 : null;
41 }
42
43 /**
44 * Starts the stopwatch. If the stopwatch is already started this will
45 * restart the stopwatch.
46 */
47 public void start() {
48 start = mxBean.getCurrentThreadCpuTime();
49 }
50
51 /**
52 * Stops the stopwatch and return the elapsed CPU time in nanoseconds.
53 * Should be called only on started stopwatches.
54 *
55 * @return the elapsed CPU time in nanoseconds. When called on non-started
56 * stopwatches (either because {@link #start()} was never called or
57 * {@link #stop()} was called after the last call to
58 * {@link #start()}) this method will return 0.
59 */
60 public long stop() {
61 long cpuTime = readout();
62 start = 0;
63 return cpuTime;
64 }
65
66 /**
67 * Return the elapsed CPU time in nanoseconds. In contrast to
68 * {@link #stop()} the stopwatch will continue to run after this call.
69 *
70 * @return the elapsed CPU time in nanoseconds. When called on non-started
71 * stopwatches (either because {@link #start()} was never called or
72 * {@link #stop()} was called after the last call to
73 * {@link #start()}) this method will return 0.
74 */
75 public long readout() {
76 return (start == 0) ? 0 : mxBean.getCurrentThreadCpuTime() - start;
77 }
78 }