leveldb.net对象读写封装

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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, );
mDataBase.Put(Encoding.UTF8.GetBytes(key), buffer.Array, , 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 > )
{
result = Formater.Deserialize(type, buffer, , (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 = * * ; public FormaterBase()
{
for (int i = ; i < ; i++)
{
mBufferPool.Push(new FormaterBuffer(BUFFER_SIZE));
}
}
public FormaterBuffer Pop()
{
lock (mBufferPool)
{
if(mBufferPool.Count>)
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, , 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, , 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 = ; 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 ;
try
{
var length = (long)lengthPtr;
var valueNative = (byte*)valuePtr.ToPointer();
Marshal.Copy((IntPtr)valuePtr, buffer, , (int)length);
return length;
}
finally
{
LevelDBInterop.leveldb_free(valuePtr); }
}