Threading / random number problem

[Mark Rae]

Hi,

My R&D department has asked me to look at threading in a Web Service written
in C#, so I came up with the following code:

using System;
using System.Componen tModel;
using System.Threadin g;
using System.Web.Serv ices;

namespace CWSThreading
{
public class CThreading : System.Web.Serv ices.WebService
{
private double mdThread1;
private double mdThread2;

public CThreading()
{
//CODEGEN: This call is required by the ASP.NET Web Services Designer
InitializeCompo nent();
}

[WebMethod]
public string TestThreading()
{
string strOutput = "";

Thread thread1 = new Thread(new ThreadStart(Ran domNumber1));
thread1.Start() ;
strOutput += "Result from 1st thread: " + mdThread1.ToStr ing() + "\n";

Thread thread2 = new Thread(new ThreadStart(Ran domNumber2));
thread2.Start() ;
strOutput += "Result from 2nd thread: " + mdThread2.ToStr ing() + "\n";

return strOutput;
}

protected void RandomNumber1()
{
System.Random rndNumber = new Random((int)Dat eTime.Now.Ticks );
mdThread1 = rndNumber.NextD ouble();
}

protected void RandomNumber2()
{
System.Random rndNumber = new Random((int)Dat eTime.Now.Ticks );
mdThread2 = rndNumber.NextD ouble();
}
}
}

This is being called by a Windows app to which a web reference has been
added pointing to the above web service. A simple form with a button runs
the following code:

using TestWSThreading .wsThreading;

private void cmdTestWSThread ing_Click(objec t sender, System.EventArg s e)
{
wsThreading.CTh reading wsTestThreading = new CThreading();
string strOutput = wsTestThreading .TestThreading( );
MessageBox.Show (strOutput);
wsTestThreading = null;
}
If I set a breakpoint anywhere in the above code which causes me to step
through it, it always returns different random numbers e.g.:

Result from 1st thread: 0.5133791689357 62
Result from 2nd thread: 0.2027999298660 08

However, if I remove the breakpoint so that the web service runs "normally",
I always get the following result:

Result from 1st thread: 0
Result from 2nd thread: 0

Any assistance gratefully received.

Best regards,

Mark Rae

[Mark Rae]

"Jon Skeet [C# MVP]" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@msnews.micros oft.com...

That's not changed the seed at all - that's just divided the *result*
by the hash code.
Correct.
Instead, it would be better to have *one* random number generator, and
serialize access to it. You only need to have one seed then, and using
the current time for that is reasonable.

Why would this be better?

[Jon Skeet [C# MVP]]

Mark Rae <ma**@markrae.c o.uk> wrote:

"Jon Skeet [C# MVP]" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@msnews.micros oft.com...

That's not changed the seed at all - that's just divided the *result*
by the hash code.

Correct.

Instead, it would be better to have *one* random number generator, and
serialize access to it. You only need to have one seed then, and using
the current time for that is reasonable.

Why would this be better?

Well, *anything* would be better than just dividing by the hash.
However, seeding the random number generator from something other than
the thread hash would be good, as the thread hash is relatively
predictable.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too