Encapsulating boost::random for ease of usage to replace rand()

Question

Hello, for my program I need pseudo random integers with different ranges. Until now I used the rand() function but it has it's limitations.

I found the boost::random library to be a much better replacement but I didn't want to create random generators all over the place.
( I need random integers in many classes, because it's a stress test software that makes every decision pseudo-randomly ( -> a test run has to be repeatable by setting the same start seed ) ).

That's why I capsuled boost::random away in my own class.

The idea behind this is to ease the use so that it is almost as straightforward as the C++ rand() method

#include "boost/shared_ptr.hpp"
#include "boost/random.hpp"

class Random{
public:
   typedef boost::shared_ptr< Random > randomPtr;
   typedef boost::mt19937 randomGeneratorType;

   static randomPtr Get(){
      static randomPtr randomGen( new RandomGenerator() );
      return randomGen;
   }

   void SetSeed(int seed){
      randomGenerator.seed( seed );
   }

   int Random( int lowerLimit, int upperLimit ){
   boost::uniform_int<> distribution( lowerLimit, upperLimit );
   boost::variate_generator< randomGeneratorType&, boost::uniform_int<> >
   LimitedInt( randomGenerator , distribution );
   return LimitedInt();
   }

private:
   // prevent creation of more than one object of the LogManager class
   // use the Get() method to get a shared_ptr to the object
  Random():
    randomGenerator() //initialize randomGenerator with default constructor
  {}

  RandomGenerator( const RandomGenerator& orig ){};

  randomGeneratorType randomGenerator;
};

Generating a random number within a given range will now be as easy as

#include "Random.h"
  Random::Get()->SetSeed( 123123 );  // If you want to make the run repeatable
  int dice = Random::Get()->Random(1,6);

Question:
Is there anything wrong with this way of generating random numbers?
Large overhead I didn't recognize ?
Pure Evil or outdated programming technique ?

( I'm still new to c++ and want to improve my skills, and I have found that Stack overflow is the best place to get high quality advice )

Answer 1

I'd say this looks fine -- this way you can easily replace your random generation algo should it be needed.

Answer 2

You've essentially wrapped your generator in a singleton, introducing all the problems that singletons and global variables carry. For example, you'd have difficulty getting multiple stress tests running in parallel, as your implementation isn't thread safe.

But the main problem that I see is that your wrapper isn't simpler than just using boost::random without the wrapper.

Answer 3

You could probably avoid Get(). This is purely subjective, to me. I would prefer a calling mechanism like Random::Seed() and Random::Next() or Random::Next(min,max). There aren't too many function in Random so you could make them all static functions.

Here's a simple implementation. But bear in mind that this is considering you're using this in a single-threaded environment. For multi-threaded environment it's better to not have it as a singleton.

class Random
{
public:
    typedef boost::mt19937 RandomGeneratorType;

    static void Seed(int seed)
    {
        s_randGen.seed(seed);
    }

    static int NextInt(int min_val, int max_val)
    {
        boost::uniform_int<> distribution(min_val, max_val);boost::variate_generator< randomGeneratorType&, boost::uniform_int<> >
        return LimitedInt( s_randGen , distribution );;
    }
private:
    static RandomGeneratorType s_randGen;
};

Random::RandomGeneratorType Random::s_randGen;

Answer 4

You can also try something like create entity in a container and random shuffle them.

void GenerateRandomString(vector& container, int size_of_string, unsigned long long num_of_records, int thread_id) { srandom(time(0)); random(); for(unsigned long long int i=0; i < num_of_records; ++i) { stringstream str_stream; str_stream.clear(); str_stream << left << setfill('x') << setw(size_of_string-4); str_stream << num_of_records+i+1 << "-" << thread_id; container.push_back(str_stream.str()); } random_shuffle(container.begin(), container.end()); }

Answer 5

Joe Gauterin demonstrated the issue, however it didn't offered any solution :)

The problem with shared state is the absence of reentrance: ie, executing twice the same method does not provide the same result. This is particularly critical in multithreaded situations because the global state may not always change at the same point in the program, thus leading to inconsistent results from one run to another.

The solution is that each simulation should have its own "state" and then you would avoid the shared state.

This can be accomplished in a number of ways: you could still use a "global" state but make it local to a thread, for example, thus the threads would not step on each others toes.

The cleaner version, however, consists in storing this state somewhere, and the easier way is to have some kind of Context class, instantiated once per simulation, and which is an aggregate of the state of the simulation (for simulation-wide state).

With that in mind:

class Context
{
public:
  typedef boost::mt19937 RandomGeneratorType;

  void SetSeed(int seed){
     rg.seed( seed );
  }

  int Next( int lowerLimit, int upperLimit ) {
    boost::uniform_int<> distribution( lowerLimit, upperLimit );
    boost::variate_generator< randomGeneratorType&, boost::uniform_int<> >
    LimitedInt( rg, distribution );
    return LimitedInt();
  }

private:
  RandomGeneratorType rg;
};

Then, pass the Context instance around in your simulation, and you can run as many as you wish in parallel.