Bits of .NET

♻️ Stop Allocating Temporary Arrays

new byte[1024] allocates and GC collects. ArrayPool<T> reuses arrays. Zero allocation for temporary buffers. Huge GC reduction.

📝 Basic ArrayPool Usage

using System.Buffers;

// Rent array (might be larger than requested)
byte[] buffer = ArrayPool.Shared.Rent(1024);
try
{
    // Use buffer
    await stream.ReadAsync(buffer, 0, 1024);
    Process(buffer);
}
finally
{
    // Return to pool (must always return!)
    ArrayPool.Shared.Return(buffer);
}

// Clear buffer before returning (if needed)
ArrayPool.Shared.Return(buffer, clearArray: true);

🎯 Real-World Example

public async Task ProcessLargeFileAsync(string path)
{
    byte[] buffer = ArrayPool.Shared.Rent(81920); // 80KB
    try
    {
        using var fs = File.OpenRead(path);
        int bytesRead;
        while ((bytesRead = await fs.ReadAsync(buffer, 0, buffer.Length)) > 0)
        {
            await ProcessChunkAsync(buffer.AsMemory(0, bytesRead));
        }
    }
    finally
    {
        ArrayPool.Shared.Return(buffer);
    }
}

// Custom pool for specific sizes
var customPool = ArrayPool.Create(maxArrayLength: 1024, maxArraysPerBucket: 50);

💡 Performance Impact

• Without pool: 1M allocations → 1M GC collections
• With pool: 1M uses → 0 allocations after warmup
• Perfect for network buffers, parsing, serialization
• Works with Span<T> and Memory<T>
• Must return rented arrays (use try/finally)