Optimize memory allocations (#98702) (#99542)

* Optimize memory allocations (#98702)

* Use `UTF8.GetMaxCharCount`

* Optimize memory allocations (#98702)

* Use `UTF8.GetMaxCharCount`

* Optimize netfx/netstandard 2.0 cases too

* Fix formatting

* Fix build error

---------

Co-authored-by: Tarek Mahmoud Sayed <tarekms@microsoft.com>

src/libraries/Microsoft.Extensions.Logging.Console/src/JsonConsoleFormatter.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Buffers;
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
@@ -81,11 +82,30 @@ private void WriteInternal(IExternalScopeProvider? scopeProvider, TextWriter tex
  writer.WriteEndObject();
  writer.Flush();
  }
-#if NET
- textWriter.Write(Encoding.UTF8.GetString(output.WrittenMemory.Span));
-#else
- textWriter.Write(Encoding.UTF8.GetString(output.WrittenMemory.Span.ToArray()));
-#endif
+
+ var messageBytes = output.WrittenMemory.Span;
+ var logMessageBuffer = ArrayPool<char>.Shared.Rent(Encoding.UTF8.GetMaxCharCount(messageBytes.Length));
+ try
+ {
+ #if NET
+ var charsWritten = Encoding.UTF8.GetChars(messageBytes, logMessageBuffer);
+ #else
+ int charsWritten;
+ unsafe
+ {
+ fixed (byte* messageBytesPtr = messageBytes)
+ fixed (char* logMessageBufferPtr = logMessageBuffer)
+ {
+ charsWritten = Encoding.UTF8.GetChars(messageBytesPtr, messageBytes.Length, logMessageBufferPtr, logMessageBuffer.Length);
+ }
+ }
+ #endif
+ textWriter.Write(logMessageBuffer, 0, charsWritten);
+ }
+ finally
+ {
+ ArrayPool<char>.Shared.Return(logMessageBuffer);
+ }
  }
  textWriter.Write(Environment.NewLine);
  }