Correct way to use Random in multithread application [duplicate]

Question

Ok. Here is what I know that won't work:

int Rand() {     //will return the same number over and over again     return new Random().Next(); }  static Random rnd=new Random();  int Rand() {     //if used like this from multiple threads, rnd will dissintegrate      //over time and always return 0     return rnd.Next(); } 

This will work correctly, but if used by multiple threads, the CPU usage goes way up, which I don't want, and which I think is not necessary:

int Rand() {     lock(rnd)     {         return rnd.Next();     } } 

So, is there a thread-safe Random class for c#, or a better way to use it?

Answer 1

I use something like this:

public static class StaticRandom {     static int seed = Environment.TickCount;      static readonly ThreadLocal<Random> random =         new ThreadLocal<Random>(() => new Random(Interlocked.Increment(ref seed)));      public static int Rand()     {         return random.Value.Next();     } } 

Answer 2

readonly ThreadLocal<Random> random =      new ThreadLocal<Random>(() => new Random(GetSeed()));  int Rand() {     return random.Value.Next(); }  static int GetSeed() {     return Environment.TickCount * Thread.CurrentThread.ManagedThreadId; } 

(shamelessly stolen from the comment of Jeroen Vannevel)