    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
    024     * elapsed since some fixed but arbitrary point in time.
    025     *
    026     * @author Kevin Bourrillion
    027     * @since 10.0
    028     *     (<a href="http://code.google.com/p/guava-libraries/wiki/Compatibility"
    029     *     >mostly source-compatible</a> since 9.0)
    030     */
    031    @Beta
    032    @GwtCompatible
    033    public abstract class Ticker {
    034      /**
    035       * Constructor for use by subclasses.
    036       */
    037      protected Ticker() {}
    038
    039      /**
    040       * Returns the number of nanoseconds elapsed since this ticker's fixed
    041       * point of reference.
    042       */
    043      public abstract long read();
    044
    045      /**
    046       * A ticker that reads the current time using {@link System#nanoTime}.
    047       *
    048       * @since 10.0
    049       */
    050      public static Ticker systemTicker() {
    051        return SYSTEM_TICKER;
    052      }
    053
    054      private static final Ticker SYSTEM_TICKER = new Ticker() {
    055        @Override
    056        public long read() {
    057          return Platform.systemNanoTime();
    058        }
    059      };
    060    }