How Can I Create a Thread-Safe Random Number Generator in C#?

Ensuring Thread Safety with C#'s Random Number Generator

C#'s built-in Random.Next() method is not thread-safe. Using it in multithreaded applications can lead to incorrect results due to race conditions. Fortunately, creating a thread-safe version is straightforward.

A Thread-Safe Random Number Generator

The following ThreadSafeRandom class provides a solution using thread-static variables to guarantee thread safety. Each thread gets its own independent Random instance.

<code class="language-csharp">public class ThreadSafeRandom
{
    private static readonly Random _global = new Random();
    [ThreadStatic] private static Random _local;

    public int Next()
    {
        if (_local == null)
        {
            int seed;
            lock (_global)
            {
                seed = _global.Next();
            }
            _local = new Random(seed);
        }

        return _local.Next();
    }
}</code>

Seed Management for Unique Random Numbers

A common problem with multiple Random instances is generating similar or identical numbers, especially when created in quick succession. This implementation addresses this by using a global Random instance (_global) to generate unique seeds for each thread-local Random instance (_local). The lock statement prevents race conditions when accessing the global Random for seed generation.

This method ensures distinct seeds for each thread, resulting in truly random and independent number sequences. Developers can now safely use random number generation within multithreaded applications, avoiding the pitfalls of non-thread-safe approaches.

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