Why Does My C# Random Number Generator Produce the Same Sequence Across Multiple Objects?

Understanding Random Number Generation in C# and Avoiding Sequence Repetition

This article addresses a common issue in C#: multiple instances of the Random class generating identical random number sequences. The Random class, while designed for generating seemingly unpredictable numbers, relies on a seed value for its internal algorithm. If multiple Random objects are created in quick succession, they often receive similar seed values (often based on the system clock), resulting in identical output sequences.

The Problem: Multiple Random Instances

Creating a new Random instance for each object needing random numbers is the root cause. Because the seed values are close together, the generated sequences are nearly identical.

The Solution: A Single, Shared Random Instance

The solution is straightforward: create a single Random instance and share it among all objects requiring random numbers. This ensures that each object draws from the same, evolving sequence, preventing the repetition problem.

Here's how to implement this using a static member:

class A
{
    private static readonly Random rnd = new Random(); // Static, read-only instance

    public void Count()
    {
        int r1 = rnd.Next(-1, 1);
        int r2 = rnd.Next(-1, 1);
    }
}

class B
{
    List<A> listOfA = new List<A>();

    public void DoSomething()
    {
        foreach (A aClass in listOfA)
        {
            aClass.Count();
        }
    }
}

By using a static readonly field, we ensure a single Random instance is created once and shared across all instances of class A. This eliminates the risk of duplicate seed values and guarantees unique random number sequences for each call to rnd.Next(). This approach produces truly random and distinct sequences for each A object.

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