Is C#'s Random.Next() Thread-Safe, and How Can You Create a Thread-Safe Alternative?

Thread safety issues in C# random number generator

In software development, ensuring safe access to shared resources in a multi-threaded environment is crucial. C#'s Random.Next() method is used to generate random numbers, but its thread safety is worth exploring.

Random.Next() thread-safe?

No. If multiple threads use the same Random.Next() instance at the same time, this can lead to unpredictable behavior and possibly even a series of zero values.

Create a thread-safe random number generator

In order to create a thread-safe version of the Random class, the following approach is recommended:

<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>

How it works:

This class achieves thread safety by maintaining a unique static Random instance for each thread. When a new thread accesses this class, it generates a seed value from the global Random instance, ensuring that the sequence is unique per thread.

Solved Random’s minor issues

Random class also has a feature: if multiple instances are created within a short period of time (within 15 milliseconds), they may return the same sequence. To mitigate this problem, use global Random instances to generate seeds to prevent conflicts.

Conclusion:

Understanding the thread-safety limitations of C# Random.Next() and implementing a thread-safe version can ensure reliable random number generation in multi-threaded applications.

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