Question

I’m not asking if these are truly random. I just wanted to know if two users hit the a page at the same time can they get the same random number? I’m thinking if i run this on a multicore server will i generate the same randon number a good amount of time due to syncing or whatever other reasons?

public static class SBackend
{
    static Random randObj = null;
    public static void init()
    {
        randObj = new Random((int)DateTime.Now.ToBinary());
        runFirstTime();
    }

    public static long getRandomId()
    {
        long randNum = (long)randObj.Next() << 33;
        randNum |= (uint)randObj.Next() << 2;
        randNum |= (uint)randObj.Next() & 3;
        return randNum;
    }
}

Answer 1

Yes it is possible for that to generate the same numbers. The seed adds nothing (it is time based by default anyway).

Also – if it is static, you should synchronize it (Next is not thread-safe):

static readonly Random rand = new Random();
public static int NextInt32() {
    lock(rand) { return rand.Next();}
}
public static long NextInt64() {
    lock(rand) { // using your algorithm...
        long randNum = (long)rand.Next() << 33;
        randNum |= (uint)rand.Next() << 2;
        randNum |= (uint)rand.Next() & 3;
        return randNum;
    }
}

This can still generate the same number by coincidence of course…

Perhaps consider a cryptographic random number generator if entropy is important.