C# Performance: Using the fixed Keyword for Memory Control

Why Memory Control Matters: A Real-World Scenario

Picture this: you’re debugging a high-performance application that processes massive datasets in real-time. The profiler shows sporadic latency spikes, and after hours of investigation, you pinpoint the culprit—garbage collection (GC). The GC is relocating objects in memory, causing your application to pause unpredictably. You need a solution, and you need it fast. Enter the fixed keyword, a lesser-known but incredibly powerful tool in C# that can help you take control of memory and eliminate those GC-induced hiccups.

In this article, we’ll explore how the fixed keyword works, when to use it, and, just as importantly, when not to. We’ll also dive into real-world examples, performance implications, and security considerations to help you wield this tool effectively.

What is the fixed Keyword?

At its core, the fixed keyword in C# is about stability—specifically, stabilizing the memory address of an object. Normally, the garbage collector in .NET can move objects around in memory to optimize performance. While this is great for most use cases, it can be a nightmare when you need a stable memory address, such as when working with pointers or interop scenarios.

The fixed keyword temporarily “pins” an object in memory, ensuring that its address remains constant for the duration of a block of code. This is particularly useful in unsafe contexts where you’re dealing with pointers or calling unmanaged code that requires a stable memory address.

How Does the fixed Keyword Work?

Here’s a basic example to illustrate the syntax and functionality of fixed:

unsafe
{
    int[] array = new int[10];

    fixed (int* p = array)
    {
        // Use the pointer 'p' to access the array directly
        for (int i = 0; i < 10; i++)
        {
            p[i] = i * 2; // Direct memory access
        }
    }
}

In this example:
    

        

            

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