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受限于当时的基础设施, 只能做到这样的程度: C# Protobuf如何做到0分配内存的序列化

但是Protobuf 3.13开始提供对Span的支持, 就意味着可以真正做到0分配内存, 对GC非常友好:

• Add ParseFrom(ReadOnlySequence<byte>) method to enable GC friendly
  parsing with reduced allocations and buffer copies. (#7351)
• Add support for serialization directly to a IBufferWriter<byte> or
  to a Span<byte> to enable GC friendly serialization.
  The new API is available as extension methods on the IMessage type. (#7576)

Protobuf 3.14也修改了ByteString:

• annotate ByteString.CopyFrom(ReadOnlySpan) as SecuritySafeCritical (#7701)

代码的例子也很简单:

//反序列化
var span = new ReadOnlySequence<byte>(array);
var message = MessageTest.Parser.ParseFrom(span);

//序列化
var outputSpan = new Span<byte>(destArray, 0, message.CalculateSize());
message.WriteTo(outputSpan);

需要安装Protobuf 3.14.0以上版本

我们的测试代码, 序列化反序列化1W次, 看看内存分配:

static void Main(string[] args)
{
     var array = new byte[0];
     var destArray = new byte[1024];
     for (int i = 0; i < 10000; ++i) 
     {
          var span = new ReadOnlySequence<byte>(array);
          var message = MessageTest.Parser.ParseFrom(span);

          message.L1 = 1112121;
          message.L2 = 231243452324234;

          var outputSpan = new Span<byte>(destArray, 0, message.CalculateSize());
          message.WriteTo(outputSpan);
     }
}

然后sampling的结果:

只有那个反序列化的对象是被new出来的, 就是我们想要的效果, 建议都升级一下.