error "Resource temporarily unavailable" when calculating hand by hand

[olegkopy]

Starting with two ranges, I want to calculate a matrix of hand equities, with individual hand-vs-hand values.

I do this simply in a double loop and constructing a length-2 vector of CardRange's, using 1 thread for each evaluation, like this :

for(h1 in range1){
   for(h2 in range2){
       ...
       std::vector<omp::CardRange> hands{h1, h2};

        eq.start(hands, board, 0, true, 5e-5, nullptr, 0.2, 1);
        eq.wait();
        auto r = eq.getResults();
   }
}

When running this on Linux, I sometimes get a runtime error

terminate called after throwing an instance of 'std::system_error'
what(): Resource temporarily unavailable

Which I assume has something to do with resource acquisition for the threads, although I don't understand how this happens considering I'm starting only 1 thread per caluclation and waiting for each to finish. Is it perhaps a more direct way to do hand-vs-hand evaluations without using the threading functionality?