Multithreaded program works only with print statements

I wish I could have thought of a more descriptive title, but that is the case. I've got some code that I'd like to do some image processing with. I also need to get some statistical data from those processed images, and I'd like to do that on a separate thread so my main thread can keep doing image processing.

All that aside, here's my code. It shouldn't really be relevant, other than the fact that my Image class wraps an OpenCV Mat (though I'm not using OMP or anything, as far as I'm aware):

#include <thread>
#include <iostream>
#include <vector>
using namespace std;

//Data struct
struct CenterFindData{
    //Some images I'd like to store
    Image in, bpass, bpass_thresh, local_max, tmp;
    //Some Data (Particle Data = float[8])
    vector<ParticleData> data;
    //My thread flag
    bool goodToGo{ false };
    //Constructor
    CenterFindData(const Image& m);
};

vector<ParticleData> statistics(CenterFindData& CFD);
void operate(vector<CenterFindData> v_CFD);


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void operate(vector<CenterFindData> v_CFD){
    //Thread function, gathers statistics on processed images
    thread T( [&](){
        int nProcessed(0);
        for (auto& cfd : v_CFD){
            //Chill while the images are still being processed
            while (cfd.goodToGo == false){ 
                 //This works if I uncomment this print statement
                /*cout << "Waiting" << endl;*/ 
            }
            cout << "Statistics gathered from " << nProcessed++ << " images" << endl;
            //This returns vector<ParticleData>
            cfd.data = m_Statistics(cfd);
        }
    });

    //Run some filters on the images before statistics
    int nProcessed(0);
    for (auto& cfd : v_CFD){
        //Preprocess images
        RecenterImage(cfd.in);
        m_BandPass(cfd);
        m_LocalMax(cfd);
        RecenterImage(cfd.bpass_thresh);
        //Tell thread to do statistics, on to the next
        cfd.goodToGo = true;
        cout << "Ran filters on " << nProcessed++ << " images" << endl;
    }

    //Join thread
    T.join();
}

I figure that the delay from cout is avoid some race condition I otherwise run into, but what? Because only one thread modified the bool goodToGo, while the other checks it, should that be a thread safe way of "gating" the two functions?

Sorry if anything is unclear, I'm very new to this and seem to make a lot of obvious mistakes WRT multithreaded programming.

Thanks for your help

• john