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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    }