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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.MICROSECONDS; import static java.util.concurrent.TimeUnit.MILLISECONDS; import static java.util.concurrent.TimeUnit.NANOSECONDS; import static java.util.concurrent.TimeUnit.SECONDS; import com.google.common.annotations.Beta; import com.google.common.annotations.GwtCompatible; import com.google.common.annotations.GwtIncompatible; import java.util.concurrent.TimeUnit; /** * An object that measures elapsed time in nanoseconds. It is useful to measure * elapsed time using this class instead of direct calls to {@link * System#nanoTime} for a few reasons: * * <ul> * <li>An alternate time source can be substituted, for testing or performance * reasons. * <li>As documented by {@code nanoTime}, the value returned has no absolute * meaning, and can only be interpreted as relative to another timestamp * returned by {@code nanoTime} at a different time. {@code Stopwatch} is a * more effective abstraction because it exposes only these relative values, * not the absolute ones. * </ul> * * <p>Basic usage: * <pre> * Stopwatch stopwatch = new Stopwatch().{@link #start start}(); * doSomething(); * stopwatch.{@link #stop stop}(); // optional * * long millis = stopwatch.{@link #elapsedMillis elapsedMillis}(); * * log.info("that took: " + stopwatch); // formatted string like "12.3 ms" * </pre> * * <p>Stopwatch methods are not idempotent; it is an error to start or stop a * stopwatch that is already in the desired state. * * <p>When testing code that uses this class, use the {@linkplain * #Stopwatch(Ticker) alternate constructor} to supply a fake or mock ticker. * <!-- TODO(kevinb): restore the "such as" --> This allows you to * simulate any valid behavior of the stopwatch. * * <p><b>Note:</b> This class is not thread-safe. * * @author Kevin Bourrillion * @since 10.0 */ @Beta @GwtCompatible(emulated=true) public final class Stopwatch { private final Ticker ticker; private boolean isRunning; private long elapsedNanos; private long startTick; public long elapsed(TimeUnit desiredUnit) { return desiredUnit.convert(elapsedNanos(), NANOSECONDS); } /** * 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 (but does not start) a new stopwatch using {@link System#nanoTime} * as its time source. */ public Stopwatch() { this(Ticker.systemTicker()); } /** * Creates (but does not start) a new stopwatch, using the specified time * source. */ public Stopwatch(Ticker ticker) { this.ticker = checkNotNull(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. */ public Stopwatch start() { checkState(!isRunning); 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. */ public Stopwatch stop() { long tick = ticker.read(); checkState(isRunning); 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 */ 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. * * <p>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. */ public long elapsedTime(TimeUnit desiredUnit) { return desiredUnit.convert(elapsedNanos(), NANOSECONDS); } /** * Returns the current elapsed time shown on this stopwatch, expressed * in milliseconds, with any fraction rounded down. This is identical to * {@code elapsedTime(TimeUnit.MILLISECONDS}. */ public long elapsedMillis() { return elapsedTime(MILLISECONDS); } /** * Returns a string representation of the current elapsed time; equivalent to * {@code toString(4)} (four significant figures). */ @GwtIncompatible("String.format()") @Override public String toString() { return toString(4); } /** * Returns a string representation of the current elapsed time, choosing an * appropriate unit and using the specified number of significant figures. * For example, at the instant when {@code elapsedTime(NANOSECONDS)} would * return {1234567}, {@code toString(4)} returns {@code "1.235 ms"}. */ @GwtIncompatible("String.format()") public String toString(int significantDigits) { 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 String.format("%." + significantDigits + "g %s", value, abbreviate(unit)); } private static TimeUnit chooseUnit(long nanos) { 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"; default: throw new AssertionError(); } } }