src/Lucene.Net.Core/Util/InfoStream.cs

using System;
using System.Diagnostics;

namespace Lucene.Net.Util
{
    /*
     * Licensed to the Apache Software Foundation (ASF) under one or more
     * contributor license agreements.  See the NOTICE file distributed with
     * this work for additional information regarding copyright ownership.
     * The ASF licenses this file to You 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.
     */

    // javadocs
    // javadocs

    /// <summary>
    /// Debugging API for Lucene classes such as <seealso cref="IndexWriter"/>
    /// and <seealso cref="SegmentInfos"/>.
    /// <p>
    /// NOTE: Enabling infostreams may cause performance degradation
    /// in some components.
    ///
    /// @lucene.internal
    /// </summary>
    public abstract class InfoStream : IDisposable, ICloneable
    {
        /// <summary>
        /// Instance of InfoStream that does no logging at all. </summary>
        public static readonly InfoStream NO_OUTPUT = new NoOutput();

        private sealed class NoOutput : InfoStream
        {
            public override void Message(string component, string message)
            {
                Debug.Assert(false, "message() should not be called when isEnabled returns false");
            }

            public override bool IsEnabled(string component)
            {
                return false;
            }

            public override void Dispose()
            {
            }
        }

        /// <summary>
        /// prints a message </summary>
        public abstract void Message(string component, string message);

        /// <summary>
        /// returns true if messages are enabled and should be posted to <seealso cref="#message"/>. </summary>
        public abstract bool IsEnabled(string component);

        private static InfoStream DefaultInfoStream = NO_OUTPUT;

        /// <summary>
        /// The default {@code InfoStream} used by a newly instantiated classes. </summary>
        /// <seealso cref= #setDefault  </seealso>
        public static InfoStream Default
        {
            get
            {
                lock (typeof(InfoStream))
                {
                    return DefaultInfoStream;
                }
            }
            set
            {
                lock (typeof(InfoStream))
                {
                    if (value == null)
                    {
                        throw new System.ArgumentException("Cannot set InfoStream default implementation to null. " + "To disable logging use InfoStream.NO_OUTPUT");
                    }
                    DefaultInfoStream = value;
                }
            }
        }

        public virtual void Dispose()
        {
        }

        public virtual object Clone()
        {
            try
            {
                return (InfoStream)base.MemberwiseClone();
            }
            catch (InvalidOperationException e)
            {
                throw new Exception(e.ToString(), e);
            }
        }
    }
}