[GitHub] [arrow] ovska opened a new issue, #34636: [C#] Reduce allocations when using ArrayPool

["ovska (via GitHub)" <gi...@apache.org>]

ovska opened a new issue, #34636:
URL: https://github.com/apache/arrow/issues/34636

   ### Describe the enhancement requested
   
   Quick single-use buffers are rented using [helper methods](/apache/arrow/blob/main/csharp/src/Apache.Arrow/Extensions/ArrayPoolExtensions.cs) that cause a (small) allocation on every invocation due to the delegate capturing references to the reader/writer and other related variables. This somewhat defeats the purpose of using pooled arrays, especially small ones for quick operations such as reading the message length.
   
   Here's a reference implementation for achieving roughly the same convenience without any allocations (outside the ones the pool might make):
   ```csharp
   public readonly struct ArrayLease : IDisposable
   {
       private readonly byte[] _array;
       private readonly ArrayPool<byte> _pool;
   
       public ArrayLease(byte[] array, ArrayPool<byte> pool)
       {
           _array = array;
           _pool = pool;
       }
   
       public void Dispose()
       {
           _pool.Return(_array);
       }
   }
   
   public static ArrayLease RentReturn(this ArrayPool<byte> pool, int length, out Memory<byte> buffer)
   {
       byte[] array = pool.Rent(length);
       buffer = array.AsMemory(0, length);
       return new ArrayLease(array, pool);
   }
   
   ```
   
   
   Example usage:
   ```diff
   - await Buffers.RentReturnAsync(4, async (buffer) =>
   + using (Buffers.RentReturn(4, out Memory<byte> buffer))
     {
         int footerLength;
         checked
         {
             footerLength = (int)(BaseStream.Position - offset);
         }
   
         BinaryPrimitives.WriteInt32LittleEndian(buffer.Span, footerLength);
   
         await BaseStream.WriteAsync(buffer, cancellationToken).ConfigureAwait(false);
   - }).ConfigureAwait(false);
   + }
   ```
   
   ### Component(s)
   
   C#


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Re: [I] [C#] Reduce allocations when using ArrayPool [arrow]

["CurtHagenlocher (via GitHub)" <gi...@apache.org>]

CurtHagenlocher closed issue #34636: [C#] Reduce allocations when using ArrayPool
URL: https://github.com/apache/arrow/issues/34636


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