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題目很簡單, 就是IMessage對(duì)象怎么變成Byte[]
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答案1:
msg.ToByteArray()
這肯定不符合我們的要求
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答案2:
using var memoryStream = new MemoryStream(); using var codedOutputStream = new
CodedOutputStream(memoryStream); msg.WriteTo(codedOutputStream);
codedOutputStream.Flush(); memoryStream.ToArray();
這里面memoryStream, codedOutputStream, 還有ToArray都產(chǎn)生了一個(gè)對(duì)象,
MemoryStream內(nèi)部還會(huì)多產(chǎn)生一個(gè)byte[]對(duì)象
不符合要求
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答案3:
有人說你可以給MemoryStream傳遞一個(gè)byte[] slice, 讓MemoryStream直接用byte[]
var bytes = new byte[msg.CalculateSize()]; using var memoryStream = new
MemoryStream();using var codedOutputStream = new
CodedOutputStream(memoryStream); msg.WriteTo(codedOutputStream);
codedOutputStream.Flush();
這次消息直接被序列化到bytes里面去了, 但是memoryStream對(duì)象,
codecOutputStream還有memoryStream內(nèi)部的byte[]都還在, 我就序列化了一個(gè)對(duì)象, 卻產(chǎn)生了3個(gè)垃圾對(duì)象
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所以, 來仔細(xì)看看CodedOutputStream類:
/// <summary> /// Creates a new CodedOutputStream that writes directly to the
given/// byte array. If more bytes are written than fit in the array, ///
OutOfSpaceException will be thrown./// </summary> public CodedOutputStream(byte
[] flatArray) :this(flatArray, 0, flatArray.Length) { } /// <summary> ///
Creates a new CodedOutputStream that writes directly to the given/// byte array
slice. If more bytes are written than fit in the array,/// OutOfSpaceException
will be thrown./// </summary> private CodedOutputStream(byte[] buffer, int
offset,int length) { this.output = null; this.buffer = buffer; this.position =
offset;this.limit = offset + length; leaveOpen = true; // Simple way of
avoiding trying to dispose of a null reference }
提供了一個(gè)byte[]的構(gòu)造函數(shù), 但是沒提供slice的構(gòu)造函數(shù), 好在有一個(gè)私有的構(gòu)造函數(shù)
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答案4:
這邊就不寫代碼了, 大概意思就是通過反射私有構(gòu)造函數(shù)來構(gòu)造一個(gè)CodedOutputStream對(duì)象, 來省掉MemoryStream和他內(nèi)部的byte[]
現(xiàn)在離答案已經(jīng)比較接近了
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那我們的問題是, 能不能連CodedOutputStream也省掉呢?
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答案5來了:
經(jīng)過仔細(xì)觀察, 發(fā)現(xiàn)這個(gè)類沒有使用Stream的情況下, 就只需要修改buffer, limit, 和position幾個(gè)成員就行了,
雖然是private成員, 但是C#還是能修改
下來立馬實(shí)踐
delegate void ClearCodedOutputStream(CodedOutputStream stream, byte[] buffer,
int offset, int count); static ClearCodedOutputStream ResetCodedOutputStream;
static CodedOutputStream codedOutputStream = new CodedOutputStream(new byte[10
]);static unsafe void Encode(IMessage msg, byte[] buffer) {
ResetCodedOutputStream(codedOutputStream, buffer,0, buffer.Length);
msg.WriteTo(codedOutputStream); codedOutputStream.Flush(); }static Action<T,
TValue> MakeSetter<T, TValue>(FieldInfo field) { DynamicMethod m = new
DynamicMethod("setter", typeof(void), new Type[] { typeof(T), typeof(TValue) },
typeof(Program)); ILGenerator cg = m.GetILGenerator();
cg.Emit(OpCodes.Ldarg_0); cg.Emit(OpCodes.Ldarg_1); cg.Emit(OpCodes.Stfld,
field); cg.Emit(OpCodes.Ret);return (Action<T, TValue>)m.CreateDelegate(typeof
(Action<T, TValue>)); } static void Main(string[] args) { var bufferField =
typeof(CodedOutputStream).GetField("buffer", BindingFlags.NonPublic |
BindingFlags.Instance);var limitField = typeof(CodedOutputStream).GetField("
limit", BindingFlags.NonPublic | BindingFlags.Instance); var positionField =
typeof(CodedOutputStream).GetField("position", BindingFlags.NonPublic |
BindingFlags.Instance);var setLimit = MakeSetter<CodedOutputStream, int>
(limitField);var setPosition = MakeSetter<CodedOutputStream, int>
(positionField);var setBuffer = MakeSetter<CodedOutputStream, byte[]>
(bufferField); ResetCodedOutputStream= (stream, buffer, offset, length) => { //
this.buffer = buffer;//this.position = offset; //this.limit = offset + length;
setBuffer(stream, buffer); setPosition(stream, offset); setLimit(stream, offset+
length); };
var buffer = new byte[msg.CalculateSize()]; Encode(msg, buffer); }
這個(gè)實(shí)例代碼里面, 用了一個(gè)static的全局CodedOutputStream, 真正用的時(shí)候, 肯定要保證線程安全.
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所以接下來的問題是:
1. 如何保證CodedOutputStream對(duì)象線程安全
2. 如何把var buffer = new byte[msg.CalculateSize()];這個(gè)也省掉
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這倆問題就留給讀者思考.
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