    001    /*
    002     * Copyright (C) 2011 The Guava Authors
    003     *
    004     * Licensed under the Apache License, Version 2.0 (the "License");
    005     * you may not use this file except in compliance with the License.
    006     * You may obtain a copy of the License at
    007     *
    008     * http://www.apache.org/licenses/LICENSE-2.0
    009     *
    010     * Unless required by applicable law or agreed to in writing, software
    011     * distributed under the License is distributed on an "AS IS" BASIS,
    012     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    013     * See the License for the specific language governing permissions and
    014     * limitations under the License.
    015     */
    016
    017    package com.google.common.base;
    018
    019    import com.google.common.annotations.Beta;
    020    import com.google.common.annotations.GwtCompatible;
    021
    022    /**
    023     * A time source; returns a time value representing the number of nanoseconds elapsed since some
    024     * fixed but arbitrary point in time. Note that most users should use {@link Stopwatch} instead of
    025     * interacting with this class directly.
    026     *
    027     * <p><b>Warning:</b> this interface can only be used to measure elapsed time, not wall time.
    028     *
    029     * @author Kevin Bourrillion
    030     * @since 10.0
    031     *     (<a href="http://code.google.com/p/guava-libraries/wiki/Compatibility"
    032     *     >mostly source-compatible</a> since 9.0)
    033     */
    034    @Beta
    035    @GwtCompatible
    036    public abstract class Ticker {
    037      /**
    038       * Constructor for use by subclasses.
    039       */
    040      protected Ticker() {}
    041
    042      /**
    043       * Returns the number of nanoseconds elapsed since this ticker's fixed
    044       * point of reference.
    045       */
    046      public abstract long read();
    047
    048      /**
    049       * A ticker that reads the current time using {@link System#nanoTime}.
    050       *
    051       * @since 10.0
    052       */
    053      public static Ticker systemTicker() {
    054        return SYSTEM_TICKER;
    055      }
    056
    057      private static final Ticker SYSTEM_TICKER = new Ticker() {
    058        @Override
    059        public long read() {
    060          return Platform.systemNanoTime();
    061        }
    062      };
    063    }