`ArrayPool<T>` & `MemoryPool<T>`: Reusable Buffer Pooling

1Concept

`ArrayPool<T>.Shared` rents reusable heap arrays from a thread-safe shared pool. Returning arrays after use reduces Garbage Collection Gen 0/1/2 pauses to near zero in high-throughput APIs.

2Architecture Diagram

ArrayPool<T>.Shared.Rent(4096) ──> Leases pre-allocated 4KB buffer from pool
                                      │
                                      ▼  (Process request)
ArrayPool<T>.Shared.Return(buffer) ──> Returns buffer back to pool (Zero GC Allocations!)

3Code Example

using System;
using System.Buffers;

public class ArrayPoolDemo
{
    public static void Main()
    {
        // Rent buffer of at least 1024 elements
        int[] buffer = ArrayPool<int>.Shared.Rent(1024);
        try
        {
            buffer[0] = 100;
            buffer[1] = 200;
            Console.WriteLine($"Rented buffer actual length: {buffer.Length} elements");
        }
        finally
        {
            // ClearArray: false for speed unless containing sensitive data
            ArrayPool<int>.Shared.Return(buffer, clearArray: false);
            Console.WriteLine("Buffer returned to ArrayPool.Shared cleanly.");
        }
    }
}

4Expected Output

Rented buffer actual length: 1024 elements
Buffer returned to ArrayPool.Shared cleanly.

5Key Takeaways

• ✓Always wrap rented arrays in `try-finally` to ensure they are returned.
• ✓Rented arrays may be larger than the requested size; use the requested length or Span slice.
• ✓Set `clearArray: true` when storing confidential data (passwords, tokens).