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/*
 * Copyright (C) 2008 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.base;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import static java.util.concurrent.TimeUnit.DAYS;
import static java.util.concurrent.TimeUnit.HOURS;
import static java.util.concurrent.TimeUnit.MICROSECONDS;
import static java.util.concurrent.TimeUnit.MILLISECONDS;
import static java.util.concurrent.TimeUnit.MINUTES;
import static java.util.concurrent.TimeUnit.NANOSECONDS;
import static java.util.concurrent.TimeUnit.SECONDS;

import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.concurrent.TimeUnit;

/**
 * An object that accurately measures elapsed time: the measured duration between two
 * successive readings of "now" in the same process.
 *
 * 

In contrast, wall time is a reading of "now" as given by a method like * {@link System#currentTimeMillis()}, best represented as an {@link Instant}. Such values * *

can be subtracted to obtain a {@code Duration} (such as by {@code Duration.between}), * but doing so does not give a reliable measurement of elapsed time, because wall time * readings are inherently approximate, routinely affected by periodic clock corrections. Because * this class (by default) uses {@link System#nanoTime}, it is unaffected by these changes. * *

Use this class instead of direct calls to {@link System#nanoTime} for two reasons: * *

    *
  • The raw {@code long} values returned by {@code nanoTime} are meaningless and unsafe to use * in any other way than how {@code Stopwatch} uses them. *
  • An alternative source of nanosecond ticks can be substituted, for example for testing or * performance reasons, without affecting most of your code. *
* *

Basic usage: * *

{@code
 * Stopwatch stopwatch = Stopwatch.createStarted();
 * doSomething();
 * stopwatch.stop(); // optional
 *
 * long millis = stopwatch.elapsed(MILLISECONDS);
 *
 * log.info("time: " + stopwatch); // formatted string like "12.3 ms"
 * }
* *

The state-changing methods are not idempotent; it is an error to start or stop a stopwatch * that is already in the desired state. * *

When testing code that uses this class, use {@link #createUnstarted(Ticker)} or {@link * #createStarted(Ticker)} to supply a fake or mock ticker. This allows you to simulate any valid * behavior of the stopwatch. * *

Note: This class is not thread-safe. * *

Warning for Android users: a stopwatch with default behavior may not continue to keep * time while the device is asleep. Instead, create one like this: * *

{@code
 * Stopwatch.createStarted(
 *      new Ticker() {
 *        public long read() {
 *          return android.os.SystemClock.elapsedRealtimeNanos();
 *        }
 *      });
 * }
* * @author Kevin Bourrillion * @since 10.0 */ @GwtCompatible @SuppressWarnings("GoodTime") // lots of violations public final class Stopwatch { private final Ticker ticker; private boolean isRunning; private long elapsedNanos; private long startTick; /** * Creates (but does not start) a new stopwatch using {@link System#nanoTime} as its time source. * * @since 15.0 */ public static Stopwatch createUnstarted() { return new Stopwatch(); } /** * Creates (but does not start) a new stopwatch, using the specified time source. * * @since 15.0 */ public static Stopwatch createUnstarted(Ticker ticker) { return new Stopwatch(ticker); } /** * Creates (and starts) a new stopwatch using {@link System#nanoTime} as its time source. * * @since 15.0 */ public static Stopwatch createStarted() { return new Stopwatch().start(); } /** * Creates (and starts) a new stopwatch, using the specified time source. * * @since 15.0 */ public static Stopwatch createStarted(Ticker ticker) { return new Stopwatch(ticker).start(); } Stopwatch() { this.ticker = Ticker.systemTicker(); } Stopwatch(Ticker ticker) { this.ticker = checkNotNull(ticker, "ticker"); } /** * Returns {@code true} if {@link #start()} has been called on this stopwatch, and {@link #stop()} * has not been called since the last call to {@code start()}. */ public boolean isRunning() { return isRunning; } /** * Starts the stopwatch. * * @return this {@code Stopwatch} instance * @throws IllegalStateException if the stopwatch is already running. */ @CanIgnoreReturnValue public Stopwatch start() { checkState(!isRunning, "This stopwatch is already running."); isRunning = true; startTick = ticker.read(); return this; } /** * Stops the stopwatch. Future reads will return the fixed duration that had elapsed up to this * point. * * @return this {@code Stopwatch} instance * @throws IllegalStateException if the stopwatch is already stopped. */ @CanIgnoreReturnValue public Stopwatch stop() { long tick = ticker.read(); checkState(isRunning, "This stopwatch is already stopped."); isRunning = false; elapsedNanos += tick - startTick; return this; } /** * Sets the elapsed time for this stopwatch to zero, and places it in a stopped state. * * @return this {@code Stopwatch} instance */ @CanIgnoreReturnValue public Stopwatch reset() { elapsedNanos = 0; isRunning = false; return this; } private long elapsedNanos() { return isRunning ? ticker.read() - startTick + elapsedNanos : elapsedNanos; } /** * Returns the current elapsed time shown on this stopwatch, expressed in the desired time unit, * with any fraction rounded down. * *

Note that the overhead of measurement can be more than a microsecond, so it is generally not * useful to specify {@link TimeUnit#NANOSECONDS} precision here. * * @since 14.0 (since 10.0 as {@code elapsedTime()}) */ public long elapsed(TimeUnit desiredUnit) { return desiredUnit.convert(elapsedNanos(), NANOSECONDS); } /** Returns a string representation of the current elapsed time. */ @Override public String toString() { long nanos = elapsedNanos(); TimeUnit unit = chooseUnit(nanos); double value = (double) nanos / NANOSECONDS.convert(1, unit); // Too bad this functionality is not exposed as a regular method call return Platform.formatCompact4Digits(value) + " " + abbreviate(unit); } private static TimeUnit chooseUnit(long nanos) { if (DAYS.convert(nanos, NANOSECONDS) > 0) { return DAYS; } if (HOURS.convert(nanos, NANOSECONDS) > 0) { return HOURS; } if (MINUTES.convert(nanos, NANOSECONDS) > 0) { return MINUTES; } if (SECONDS.convert(nanos, NANOSECONDS) > 0) { return SECONDS; } if (MILLISECONDS.convert(nanos, NANOSECONDS) > 0) { return MILLISECONDS; } if (MICROSECONDS.convert(nanos, NANOSECONDS) > 0) { return MICROSECONDS; } return NANOSECONDS; } private static String abbreviate(TimeUnit unit) { switch (unit) { case NANOSECONDS: return "ns"; case MICROSECONDS: return "\u03bcs"; // μs case MILLISECONDS: return "ms"; case SECONDS: return "s"; case MINUTES: return "min"; case HOURS: return "h"; case DAYS: return "d"; default: throw new AssertionError(); } } }





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