leveldb.net对象读写封装

浏览数：27 / 时间：2015年06月12日

leveldb是一个非常高效的可嵌入式K-V数据库,在.NET下有着基于win实现的包装leveldb.net;不过leveldb.net只提供了基于byte[]和string的处理,这显然会对使用的时候带来不方便,毕竟在编写应用的时候都是希望通过对象的方式来存储,如我们常见的redis,mongodb和memcached等等都提供对象方式的读写.以下主要讲解leveldb.net基础上封装一层序列化功能方便使用.

制定对象化的访问接口

为了不修改leveldb.net的代码,所以选择在他基础过行封装,为了清楚需要些什么简单地定义了一个规则

 public interface IDBManager
    {
        IFormater Formater { get; set; }

        void Set(string key, object data);

        object Get(string key, Type type);

        T Get<T>(string key);

        void Open();

        LevelDB.DB DataBase
        {
            get;
        }
       
    }

代码非常简单主要封装了GET,SET,实际上还有DELETE操作,这里偷懒就没做了:),为了提供灵活序列化规则所以在这个管理接口上还提供了一个Formater属性.下面是这相接口的详细实现:

public class LevelDBManager : IDBManager
    {

        public LevelDBManager()
        {
            
        }

        private LevelDB.DB mDataBase;

        public string Path { get; set; }

        public IFormater Formater
        {
            get;
            set;
        }

        public void Open()
        {
            mDataBase = new LevelDB.DB(Path, new Options() { CreateIfMissing = true });
          
        }

        public void Set(string key, object data)
        {

            FormaterBuffer buffer = Formater.Pop();
            try
            {

                int count = Formater.Serialize(data, buffer, 0);
                mDataBase.Put(Encoding.UTF8.GetBytes(key), buffer.Array, 0, count);
            }
            finally
            {
                Formater.Push(buffer);
            }
        }

        public object Get(string key, Type type)
        {
            FormaterBuffer buffer = Formater.Pop();
            long count;
            object result = null;
           
            try
            {
                count = mDataBase.Get(Encoding.UTF8.GetBytes(key), buffer.Array);
                if (count > 0)
                {
                    result = Formater.Deserialize(type, buffer, 0, (int)count);

                }
                return result;
            }
            finally
            {
                Formater.Push(buffer);
            }
          
        }

        public T Get<T>(string key)
        {
            return (T)Get(key, typeof(T));
        }


        public DB DataBase
        {
            get { return mDataBase; }
        }
    }

相信以上那些简知的代码也比较好理解,所以就不详细说明了.

可扩展的序列化规则

由于在使用上的需要,都习惯用些不同序列化方式来进行对象序列化,这个封装为了实现一个比较高的灵活度,所以对象序列化过程也制定了一个接口进行隔离.主要为了满足不同人的胃口.

   public interface IFormater
    {
        FormaterBuffer Pop();

        void Push(FormaterBuffer data);

        int Serialize(object data, FormaterBuffer buffer, int offset);

        object Deserialize(Type type, FormaterBuffer buffer, int offset, int count);
    }

比较简单定义了序列化和反序列化的方法,不过为了一些性能上的考虑增加了buffer的复用功能,这个设计紧紧用作需要追求这方面性能要求而准备.下面看一下json和protobuf的实现是怎样的:

 public abstract class FormaterBase:IFormater
    {
         private Stack<FormaterBuffer> mBufferPool = new Stack<FormaterBuffer>();

        const int BUFFER_SIZE = 1024 * 1024 * 1;

        public FormaterBase()
        {
            for (int i = 0; i < 20; i++)
            {
                mBufferPool.Push(new FormaterBuffer(BUFFER_SIZE));
            }
        }
        public FormaterBuffer Pop()
        {
            lock (mBufferPool)
            {
                if(mBufferPool.Count>0)
                    return mBufferPool.Pop();
                return new FormaterBuffer(BUFFER_SIZE);
            }
        }
        public void Push(FormaterBuffer data)
        {
            lock (mBufferPool)
            {
                mBufferPool.Push(data);
            }
        }
       
        public abstract int Serialize(object data, FormaterBuffer buffer, int offset);
       
        public abstract object Deserialize(Type type, FormaterBuffer buffer, int offset, int count);
        
    }

json

public class JsnoFormater:FormaterBase
    {
       
        public int Serialize(object data, byte[] buffer, int offset)
        {
            string json = Newtonsoft.Json.JsonConvert.SerializeObject(data);
            return Encoding.UTF8.GetBytes(json, 0, json.Length, buffer, offset);
        }

        public override int Serialize(object data, FormaterBuffer buffer, int offset)
        {
            string json = Newtonsoft.Json.JsonConvert.SerializeObject(data);
            return Encoding.UTF8.GetBytes(json, 0, json.Length, buffer.Array, offset);
        }

        public override object Deserialize(Type type, FormaterBuffer buffer, int offset, int count)
        {
            string value = Encoding.UTF8.GetString(buffer.Array, offset, count);
            return Newtonsoft.Json.JsonConvert.DeserializeObject(value, type);
        }
    }

protobuf

 public class ProtobufFormater:FormaterBase
    {

        public override int Serialize(object data, FormaterBuffer buffer, int offset)
        {
            buffer.Seek(offset);
            ProtoBuf.Meta.RuntimeTypeModel.Default.Serialize(buffer.Stream, data);
            return (int)buffer.Stream.Position;
        }

        public override object Deserialize(Type type, FormaterBuffer buffer, int offset, int count)
        {
            buffer.Stream.SetLength(count + offset);
            buffer.Seek(offset);
            return ProtoBuf.Meta.RuntimeTypeModel.Default.Deserialize(buffer.Stream, null, type);
        }
    }

leveldb.net的一些简单性能改造

虽然leveldb.net只以win dll的基础上包装,但在包装过程的确有些方法针对我个人来说做得并不理想,主要体现在buffer复用方面.其实get,set方法都存在这情况.

 /// <summary>
        /// Set the database entry for "key" to "value".  
        /// </summary>
        public void Put(byte[] key, byte[] value, WriteOptions options)
        {
            IntPtr error;
            LevelDBInterop.leveldb_put(this.Handle, options.Handle, key, (IntPtr)key.Length, value, (IntPtr)value.LongLength, out error);
            LevelDBException.Check(error);
            GC.KeepAlive(options);
            GC.KeepAlive(this);
        }
        public unsafe byte[] Get(byte[] key, ReadOptions options)
        {
            IntPtr error;
            IntPtr lengthPtr;
            var valuePtr = LevelDBInterop.leveldb_get(this.Handle, options.Handle, key, (IntPtr)key.Length, out lengthPtr, out error);
            LevelDBException.Check(error);
            if (valuePtr == IntPtr.Zero)
                return null;
            try
            {
                var length = (long)lengthPtr;
                var value = new byte[length];
                var valueNative = (byte*)valuePtr.ToPointer();
                for (long i = 0; i < length; ++i)
                    value[i] = valueNative[i];
                return value;
            }
            finally
            {
                LevelDBInterop.leveldb_free(valuePtr);
                GC.KeepAlive(options);
                GC.KeepAlive(this);
            }
        }

两上个方法都不支持从外部带入buffer的情况,当需要高并发操作的情况而对象序列化内容又比较大的情况下,那的确是会让人感觉到不满意.所以在这基础上添加了一些有利于buffer复用的方法来支持高并发操作下的性能需要.

 public void Put(byte[] key, byte[] value, int offset, int length, WriteOptions options)
        {
            IntPtr error;
            LevelDBInterop.leveldb_put(this.Handle, options.Handle, key, (IntPtr)key.Length, value, (IntPtr)length, out error);
            LevelDBException.Check(error);
            GC.KeepAlive(options);
            GC.KeepAlive(this);
        }
        public unsafe long Get(byte[] key, byte[] buffer, ReadOptions options)
        {
            IntPtr error;
            IntPtr lengthPtr;
            var valuePtr = LevelDBInterop.leveldb_get(this.Handle, options.Handle, key, (IntPtr)key.Length, out lengthPtr, out error);
            LevelDBException.Check(error);
            if (valuePtr == IntPtr.Zero)
                return 0;
            try
            {
                var length = (long)lengthPtr;
                var valueNative = (byte*)valuePtr.ToPointer();
                Marshal.Copy((IntPtr)valuePtr, buffer, 0, (int)length);
                return length;
            }
            finally
            {
                LevelDBInterop.leveldb_free(valuePtr);
              
            }
        }