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Subject: [Boost-users] [multiindex] Ordered index corruption
From: Chris Jewell (chris.jewell_at_[hidden])
Date: 2011-07-21 09:55:49

Hi All,

I have a problem with a multiindex ordered_non_unique index becoming corrupted :(

I am working with a multiindex that stores class objects of type Individual:

class Individual
        double I_;
        double id_;
         double getId() const;
        double getI() const;
        void setId(const std::string id);
         void setI(const double I);

            random_access< tag<bySeq> >,
            hashed_unique< tag<byId>, const_mem_fun<Individual,string,&Individual::getId> >,
            ordered_non_unique<tag<byI>, const_mem_fun<Individual,double,&Individual::getI> >

I have an algorithm that works on these data, using Individual::I to calculate a summary value across the whole dataset. An Individual i is then chosen at random, and i.I updated using the multiindex::modify method with a functor:

struct modifyI
        modifyI(double newI) : newI_(newI) {}
        void operator()(Individual& i)
        double newI_;

This calculation is then repeated many times. The actual calculation is done in parallel using MPI (Boost::MPI on top of OpenMPI), with the final reduction being broadcast to all processes. This enables each processor to make the same change to its copy of the multiindex. In *theory* this should mean that each process has a complete replicate of the multiindex.

However, I am finding that the ordered_non_unique index is becoming corrupted in that the ordering (strict less than on Individual::I) gets messed up for a few (c. 2 or 3) of the elements. Essentially, it appears that small blocks of the index get swapped round. This is not occurring simultaneously on all processes, which is odd because the same multiindex::modify method is called for each process with the same arguments.

Can anyone suggest a way I can move forward on trying to debug this?



Dr Chris Jewell
Department of Statistics
University of Warwick
Tel: +44 (0)24 7615 0778

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