Re: [Boost-users] 1.36.0 boost/random/uniform_01 Infinite[?] Loop

Subject: Re: [Boost-users] 1.36.0 boost/random/uniform_01 Infinite[?] Loop
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2008-10-16 19:39:09

AMDG

Dave Steenburgh wrote:
> > Or better, a minimal example to try?
>
> I'd like to think I know what the problem is now, but I'm still a 
> little mystified, and I'm not sure how best to correct it.  What I 
> think I want is a correction to or replacement for my wrapper class, 
> but I definitely want a second opinion.  (Maybe a third and a fourth, 
> too...)
>
> I've got a minimal-ish program that exhibits strange behavior, but it 
> doesn't get stuck.  I suspect the same phenomenon is at work here, 
> though, since it still only appears when compiling without 
> optimization.  The source is attached, and here are some of my 
> observations:  If I use ng instead of vg, there is no problem.  (Try 
> it yourself; just move the comment slashes.)  If I omit the call to 
> problemFunction, everything works.  If I decrease the number of 
> arguments problemFunction requires, everything works.  Based on that 
> info, my guess is that something the random generator needs is created 
> on the stack, and later overwritten.  However, I think if that were 
> really the problem, it would still be a problem on another platform, 
> or with optimizations enabled.

The error is in this class:

class normalGenerator : public randomGenerator
{
private:
  typedef boost::normal_distribution<> normalDistribution;
  boost::variate_generator<baseGenerator&, normalDistribution> _gen;
public:
  explicit normalGenerator(baseGenerator gen = baseGenerator(time(NULL)))
    : _gen(gen, normalDistribution()) { }
  inline virtual double operator()() { return _gen(); }
};

a) _gen stores a reference to a baseGenerator.
b) The constructor takes a baseGenerator by value, which is then 
destroyed when
  the constructor returns.

In Christ,
Steven Watanabe