Atomic State Management with Compare-And-Swap

Snippet

Atomic State Management with Compare-And-Swap

The Interlocked.CompareExchange method implements a Compare-And-Swap (CAS) operation, which is the foundation of lock-free concurrency. It atomically checks if a value matches an expected one and, if so, replaces it. This avoids the overhead of traditional locks (mutexes) and prevents thread context switching, which is critical for high-throughput systems.

snippet.cs

csharp

using System.Threading;
 
public class LockFreeStack
{
    private int _state = 0;
 
    public void UpdateState(int expected, int next)
    {
        // Spin-wait using CompareExchange for lock-free thread safety
        while (Interlocked.CompareExchange(ref _state, next, expected) != expected)
        {
            // Potential back-off logic here
            Thread.Yield();
        }
    }
}

Breakdown

while (Interlocked.CompareExchange(ref _state, next, expected) != expected)

Attempts to update the state only if the current value matches 'expected' in a single atomic step.

Thread.Yield();

Allows other threads to execute if the atomic update fails due to contention.

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Atomic State Management with Compare-And-Swap

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