optimizing-memory-allocation

.NET Memory Efficiency, Zero Allocation

A guide for APIs that minimize GC pressure and enable high-performance memory management.

Quick Reference: See QUICKREF.md for essential patterns at a glance.

1. Core Concepts

• .NET CLR GC Heap Memory Optimization
• Understanding Stack allocation vs Heap allocation
• Stack-only types through ref struct

2. Key APIs

API	Purpose	NuGet
Span<T>, Memory<T>	Stack-based memory slicing	BCL
ArrayPool<T>.Shared	Reduce GC pressure through array reuse	BCL
DefaultObjectPool<T>	Object pooling	Microsoft.Extensions.ObjectPool
MemoryCache	In-memory caching	System.Runtime.Caching

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3. Span, ReadOnlySpan

3.1 Basic Usage

// Zero Allocation when parsing strings
public void ParseData(ReadOnlySpan<char> input)
{
    // String manipulation without Heap allocation
    var firstPart = input.Slice(0, 10);
    var secondPart = input.Slice(10);
}

// Array slicing
public void ProcessArray(int[] data)
{
    Span<int> span = data.AsSpan();
    Span<int> firstHalf = span[..^(span.Length / 2)];
    Span<int> secondHalf = span[(span.Length / 2)..];
}

3.2 String Processing Optimization

// ❌ Bad example: Substring allocates new string
string part = text.Substring(0, 10);

// ✅ Good example: AsSpan has no allocation
ReadOnlySpan<char> part = text.AsSpan(0, 10);

3.3 Using with stackalloc

public void ProcessSmallBuffer()
{
    // Allocate small buffer on Stack (no Heap allocation)
    Span<byte> buffer = stackalloc byte[256];
    FillBuffer(buffer);
}

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4. ArrayPool

Reduces GC pressure by reusing large arrays.

4.1 Basic Usage

namespace MyApp.Services;

public sealed class DataProcessor
{
    public void ProcessLargeData(int size)
    {
        // Rent array (minimize Heap allocation)
        var buffer = ArrayPool<byte>.Shared.Rent(size);

        try
        {
            // Use buffer (only use up to requested size)
            ProcessBuffer(buffer.AsSpan(0, size));
        }
        finally
        {
            // Must return
            ArrayPool<byte>.Shared.Return(buffer);
        }
    }
}