add concurrency-friendly map access to fix #8

[piazzamp]

Created a new type histogram that couples a sync.RWMutex and the existing map. The type itself isn't exported (no one should be instantiating these, right?), but its Get and Set methods are. This is a significant change for consumers that create their own NaiveBayes struct without calling NewNaiveBayes.

[cdipaolo]

concurrency*

[cdipaolo]

Looks great! Thanks for doing this. I left some comments that should be somehow resolved before this gets merged but they're really small issues.

Thanks! 🐱

[cdipaolo]

Also I just remembered: could you add your consistently failing example you sent to the tests (text/bayes_test.go) under the name TestConcurrentPredictionAndLearningShouldNotFail or something similar?

Or rather modify it to make it automatable and then include it in the tests

func newTrainedModel() (*text.NaiveBayes, error) {
    c := make(chan base.TextDatapoint)
    model := text.NewNaiveBayes(c, 9, base.OnlyWords)
    errors := make(chan error)
    go model.OnlineLearn(errors)

    go func() {
        for err, more := <-errors; more; err, more = <-errors {
            if err != nil {
                fmt.Printf("Error passed: %s", err)
            }
        }
    }()
    data, err := trainingData()
    if err != nil {
        return nil, err
    }
    for _, tdp := range data {
        c <- tdp
    }
    close(c)
    return model, nil
}

[cdipaolo]

Looks great! I really appreciate all of this. If you feel like helping refactor/improve things/fix another bug any time let me know!!

[piazzamp]

will do - thanks!