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    }