（原创）《Lucene in Action 2nd Edition》Chapter11.2.2中的工具类SearcherManager翻译为C#版本

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Lucene.Net.Search;
using Lucene.Net.Index;
using Lucene.Net.Store;
using System.Runtime.CompilerServices;
using System.Threading;

namespace WheatStudio.Utility.Lucene
{
    /// <summary>
    /// 《Lucene in Action 2nd Edition》 Jun 2010
    /// Chapter 11.2.2中的工具类SearcherManager翻译为C#版本
    /// 用于多线程环境下共享IndexSearcher(IndexReader)
    /// 金思魁
    /// </summary>
    public class SearcherManager 
    {
        private IndexSearcher currentSearcher;
        private IndexWriter writer;
        private AutoResetEvent Tevent = new AutoResetEvent(false);

        public SearcherManager(Directory dir)
        {
            currentSearcher = new IndexSearcher(IndexReader.Open(dir));
            warm(currentSearcher);
        }

        public SearcherManager(IndexWriter writer)
        {
            this.writer = writer;
            currentSearcher = new IndexSearcher(writer.GetReader());
            warm(currentSearcher);
            writer.SetMergedSegmentWarmer(new MyWarmer(this.warm));
        }

        public virtual void warm(IndexSearcher searcher)
        {
            /*******************************************
             * 用户定制，做一些初始化IndexSearcher的工作
             * 每次生成新IndexSearch实例后都会触发
             * ***********************************/
        }

        private bool reopening;

        [MethodImpl(MethodImplOptions.Synchronized)]
        private void startReopen()
        {
            while (reopening)
            {
                Tevent.WaitOne();
            }
            reopening = true;
        }

        [MethodImpl(MethodImplOptions.Synchronized)]
        private void doneReopen()
        {
            reopening = false;
            Tevent.Set();
        }

        /// <summary>
        /// 在检查到Index有更新时创建新的IndexSearcher(IndexReader)
        /// 可以在每次IndexWriter更新索引后调用，也可以在执行搜索前调用
        /// 如果是用IndexWriter构造本类，即使IndexWriter未commit也能搜索到最新更改
        /// 如果使用Directory构造本类，IndexWriter调用commit后方能搜索到最新更改
        /// </summary>
        public void maybeReopen()
        {
            startReopen();
            try 
            {
                IndexSearcher searcher = get();
                try 
                {
                    IndexReader newReader = currentSearcher.GetIndexReader().Reopen();
                    if (newReader != currentSearcher.GetIndexReader())
                    {
                        IndexSearcher newSearcher = new IndexSearcher(newReader);
                        if (writer == null) 
                        {
                            warm(newSearcher);
                        }
                        swapSearcher(newSearcher);
                    }
                } 
                finally 
                {
                    release(searcher);
                }
            } 
            finally 
            {
                doneReopen();
            }
        }

        /// <summary>
        /// 获取IndexSearcher，必须和release方法配对调用
        /// </summary>
        /// <returns></returns>
        [MethodImpl(MethodImplOptions.Synchronized)]
        public IndexSearcher get() {
            currentSearcher.GetIndexReader().IncRef();
            return currentSearcher;
        }

        [MethodImpl(MethodImplOptions.Synchronized)]
        public void release(IndexSearcher searcher)
        {
            searcher.GetIndexReader().DecRef();
        }

        [MethodImpl(MethodImplOptions.Synchronized)]
        private void swapSearcher(IndexSearcher newSearcher)
        {
            release(currentSearcher);
            currentSearcher = newSearcher;
        }

        public void close()
        {
            swapSearcher(null);
        }        
    }

    public delegate void WarmDelegate(IndexSearcher reader);
    public class MyWarmer : IndexWriter.IndexReaderWarmer
    {
        public event WarmDelegate WarmEvent;

        public MyWarmer(WarmDelegate WarmEvent)
        {
            this.WarmEvent = WarmEvent;
        }

        public override void Warm(IndexReader reader)
        {
            if (WarmEvent != null)
            {
                WarmEvent(new IndexSearcher(reader));
            }
        }
    }
}