System.Random keeps on returning the same value

Question

I am using a System.Random object which is instantiated with a fixed seed all thoughout the application. I am calling the NextDouble method and after some time passed I am getting 0.0 as result.

Is there any remedy to this, has anyone else encountered this ?

EDIT: I have one seed for the whole run which is set to 1000 for convience sake. The random.NextDouble is called several hundred thousand times. It is an optimizer application and could run for couple hours, but this actually happens after 10-0 mins of execution. I have recently added little bit more random calls to the app.

Can you elaborate on "some time"? Are we talking an hour, or several days of millions of numbers? I don't imagine you've run into a problem in the actual function, but if you're in territory that's never been tested or planned for, I won't discount it immediately. — Tom Ritter, Nov 17 '08 at 15:52
possible duplicate of [Random number generator only generating one random number](http://stackoverflow.com/questions/767999/random-number-generator-only-generating-one-random-number) — Alexei Levenkov, Aug 18 '15 at 18:48

score 18 · Accepted Answer · answered Nov 17 '08 at 15:55

18

The random number generator in .NET is not thread safe. Other developers have noticed the same behaviour, and one solution is as follows (from http://blogs.msdn.com/brada/archive/2003/08/14/50226.aspx):

class ThreadSafeRandom
{
    private static Random random = new Random();

    public static int Next()
    {
       lock (random)
       {
           return random.Next();
       }
    }
}

answered Nov 17 '08 at 15:55

e.James

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It seems like you could also apply the [ThreadStatic] attribute to your Random instance, if it's a static variable in your app. – Chris Moschini Jan 08 '11 at 19:09

score 9 · Answer 2 · answered Nov 17 '08 at 15:42

9

How often are you seeding Random? It should be done only once at the start of the program.

And once seeded with a given value, it will always produce the exact same sequence.

answered Nov 17 '08 at 15:42

James Curran

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score 3 · Answer 3 · answered Nov 17 '08 at 15:56

Tomas, I ran into this "bug" before and the solution for me was to make the _rnd variable module-level:

Private Shared _rnd As System.Random()
Public Shared Function RandRange(ByVal low As Integer, ByVal high As Integer) As Integer
    If _rnd Is Nothing Then
        _rnd = New System.Random()
    End If
    Return rnd.Next(low, high)
End Function

score 3 · Answer 4 · edited May 23 '17 at 11:46

Other folks have already done a decent job explaining it and providing solutions.

Anyway, a similiar question has been answered before by Erik, check it out:

Pseudo Random Generator with same output

You also get more questions and answers related to the topic (Random Number Generators) at:

Stackoverflow.com random-number-generator

Gene

P.S. This is just to supplement the accepted answer.

Hath · Answer 5 · 2008-11-17T15:55:03.450

1

have a look at this http://msdn.microsoft.com/en-us/library/system.random.aspx it should explain why your getting the same value.

edited Nov 17 '08 at 15:55

answered Nov 17 '08 at 15:45

Hath

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The new Random(DateTime.Now.Second) option is limited to 60 distinct runs of values. – Jason Z Nov 17 '08 at 15:53
Why not just use the default constructor, and let it pick a seed for you? Guaranteed to be a better idea than _these_. – Domenic Nov 17 '08 at 15:55

System.Random keeps on returning the same value

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