001/*
002 * Copyright (C) 2008 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.base;
016
017import static com.google.common.base.Preconditions.checkNotNull;
018import static com.google.common.base.Preconditions.checkState;
019import static java.util.concurrent.TimeUnit.DAYS;
020import static java.util.concurrent.TimeUnit.HOURS;
021import static java.util.concurrent.TimeUnit.MICROSECONDS;
022import static java.util.concurrent.TimeUnit.MILLISECONDS;
023import static java.util.concurrent.TimeUnit.MINUTES;
024import static java.util.concurrent.TimeUnit.NANOSECONDS;
025import static java.util.concurrent.TimeUnit.SECONDS;
026
027import com.google.common.annotations.GwtCompatible;
028import com.google.common.annotations.GwtIncompatible;
029import com.google.errorprone.annotations.CanIgnoreReturnValue;
030import com.google.j2objc.annotations.J2ObjCIncompatible;
031import java.time.Duration;
032import java.util.concurrent.TimeUnit;
033
034/**
035 * An object that measures elapsed time in nanoseconds. It is useful to measure elapsed time using
036 * this class instead of direct calls to {@link System#nanoTime} for a few reasons:
037 *
038 * <ul>
039 *   <li>An alternate time source can be substituted, for testing or performance reasons.
040 *   <li>As documented by {@code nanoTime}, the value returned has no absolute meaning, and can only
041 *       be interpreted as relative to another timestamp returned by {@code nanoTime} at a different
042 *       time. {@code Stopwatch} is a more effective abstraction because it exposes only these
043 *       relative values, not the absolute ones.
044 * </ul>
045 *
046 * <p>Basic usage:
047 *
048 * <pre>{@code
049 * Stopwatch stopwatch = Stopwatch.createStarted();
050 * doSomething();
051 * stopwatch.stop(); // optional
052 *
053 * Duration duration = stopwatch.elapsed();
054 *
055 * log.info("time: " + stopwatch); // formatted string like "12.3 ms"
056 * }</pre>
057 *
058 * <p>Stopwatch methods are not idempotent; it is an error to start or stop a stopwatch that is
059 * already in the desired state.
060 *
061 * <p>When testing code that uses this class, use {@link #createUnstarted(Ticker)} or {@link
062 * #createStarted(Ticker)} to supply a fake or mock ticker. This allows you to simulate any valid
063 * behavior of the stopwatch.
064 *
065 * <p><b>Note:</b> This class is not thread-safe.
066 *
067 * <p><b>Warning for Android users:</b> a stopwatch with default behavior may not continue to keep
068 * time while the device is asleep. Instead, create one like this:
069 *
070 * <pre>{@code
071 * Stopwatch.createStarted(
072 *      new Ticker() {
073 *        public long read() {
074 *          return android.os.SystemClock.elapsedRealtimeNanos();
075 *        }
076 *      });
077 * }</pre>
078 *
079 * @author Kevin Bourrillion
080 * @since 10.0
081 */
082@GwtCompatible(emulated = true)
083public final class Stopwatch {
084  private final Ticker ticker;
085  private boolean isRunning;
086  private long elapsedNanos;
087  private long startTick;
088
089  /**
090   * Creates (but does not start) a new stopwatch using {@link System#nanoTime} as its time source.
091   *
092   * @since 15.0
093   */
094  public static Stopwatch createUnstarted() {
095    return new Stopwatch();
096  }
097
098  /**
099   * Creates (but does not start) a new stopwatch, using the specified time source.
100   *
101   * @since 15.0
102   */
103  public static Stopwatch createUnstarted(Ticker ticker) {
104    return new Stopwatch(ticker);
105  }
106
107  /**
108   * Creates (and starts) a new stopwatch using {@link System#nanoTime} as its time source.
109   *
110   * @since 15.0
111   */
112  public static Stopwatch createStarted() {
113    return new Stopwatch().start();
114  }
115
116  /**
117   * Creates (and starts) a new stopwatch, using the specified time source.
118   *
119   * @since 15.0
120   */
121  public static Stopwatch createStarted(Ticker ticker) {
122    return new Stopwatch(ticker).start();
123  }
124
125  Stopwatch() {
126    this.ticker = Ticker.systemTicker();
127  }
128
129  Stopwatch(Ticker ticker) {
130    this.ticker = checkNotNull(ticker, "ticker");
131  }
132
133  /**
134   * Returns {@code true} if {@link #start()} has been called on this stopwatch, and {@link #stop()}
135   * has not been called since the last call to {@code start()}.
136   */
137  public boolean isRunning() {
138    return isRunning;
139  }
140
141  /**
142   * Starts the stopwatch.
143   *
144   * @return this {@code Stopwatch} instance
145   * @throws IllegalStateException if the stopwatch is already running.
146   */
147  @CanIgnoreReturnValue
148  public Stopwatch start() {
149    checkState(!isRunning, "This stopwatch is already running.");
150    isRunning = true;
151    startTick = ticker.read();
152    return this;
153  }
154
155  /**
156   * Stops the stopwatch. Future reads will return the fixed duration that had elapsed up to this
157   * point.
158   *
159   * @return this {@code Stopwatch} instance
160   * @throws IllegalStateException if the stopwatch is already stopped.
161   */
162  @CanIgnoreReturnValue
163  public Stopwatch stop() {
164    long tick = ticker.read();
165    checkState(isRunning, "This stopwatch is already stopped.");
166    isRunning = false;
167    elapsedNanos += tick - startTick;
168    return this;
169  }
170
171  /**
172   * Sets the elapsed time for this stopwatch to zero, and places it in a stopped state.
173   *
174   * @return this {@code Stopwatch} instance
175   */
176  @CanIgnoreReturnValue
177  public Stopwatch reset() {
178    elapsedNanos = 0;
179    isRunning = false;
180    return this;
181  }
182
183  private long elapsedNanos() {
184    return isRunning ? ticker.read() - startTick + elapsedNanos : elapsedNanos;
185  }
186
187  /**
188   * Returns the current elapsed time shown on this stopwatch, expressed in the desired time unit,
189   * with any fraction rounded down.
190   *
191   * <p><b>Note:</b> the overhead of measurement can be more than a microsecond, so it is generally
192   * not useful to specify {@link TimeUnit#NANOSECONDS} precision here.
193   *
194   * <p>It is generally not a good idea to use an ambiguous, unitless {@code long} to represent
195   * elapsed time. Therefore, we recommend using {@link #elapsed()} instead, which returns a
196   * strongly-typed {@link Duration} instance.
197   *
198   * @since 14.0 (since 10.0 as {@code elapsedTime()})
199   */
200  public long elapsed(TimeUnit desiredUnit) {
201    return desiredUnit.convert(elapsedNanos(), NANOSECONDS);
202  }
203
204  /**
205   * Returns the current elapsed time shown on this stopwatch as a {@link Duration}. Unlike {@link
206   * #elapsed(TimeUnit)}, this method does not lose any precision due to rounding.
207   *
208   * @since 22.0
209   */
210  @GwtIncompatible
211  @J2ObjCIncompatible
212  public Duration elapsed() {
213    return Duration.ofNanos(elapsedNanos());
214  }
215
216  /** Returns a string representation of the current elapsed time. */
217  @Override
218  public String toString() {
219    long nanos = elapsedNanos();
220
221    TimeUnit unit = chooseUnit(nanos);
222    double value = (double) nanos / NANOSECONDS.convert(1, unit);
223
224    // Too bad this functionality is not exposed as a regular method call
225    return Platform.formatCompact4Digits(value) + " " + abbreviate(unit);
226  }
227
228  private static TimeUnit chooseUnit(long nanos) {
229    if (DAYS.convert(nanos, NANOSECONDS) > 0) {
230      return DAYS;
231    }
232    if (HOURS.convert(nanos, NANOSECONDS) > 0) {
233      return HOURS;
234    }
235    if (MINUTES.convert(nanos, NANOSECONDS) > 0) {
236      return MINUTES;
237    }
238    if (SECONDS.convert(nanos, NANOSECONDS) > 0) {
239      return SECONDS;
240    }
241    if (MILLISECONDS.convert(nanos, NANOSECONDS) > 0) {
242      return MILLISECONDS;
243    }
244    if (MICROSECONDS.convert(nanos, NANOSECONDS) > 0) {
245      return MICROSECONDS;
246    }
247    return NANOSECONDS;
248  }
249
250  private static String abbreviate(TimeUnit unit) {
251    switch (unit) {
252      case NANOSECONDS:
253        return "ns";
254      case MICROSECONDS:
255        return "\u03bcs"; // μs
256      case MILLISECONDS:
257        return "ms";
258      case SECONDS:
259        return "s";
260      case MINUTES:
261        return "min";
262      case HOURS:
263        return "h";
264      case DAYS:
265        return "d";
266      default:
267        throw new AssertionError();
268    }
269  }
270}