Vector [] operation (read only) thread safety

Question

I have created a vector and filled data as part of an object initialization. The vector will not be modified after initialization. The declaration of the vector is

std::vector<AnalyticalChuckRing_t> m_analyticalRings;

We will call a method named GroupCirclesByRing from multiple async tasks. The following lines of code access the vector object in this method. I am almost sure that these statement does not need protection as it does not modify the object. Where can I find the documentation to ensure that thread synchronization is not required?

 auto GetRingAndAngle = [=](const CPoint& point)
            {
                double dDistance = DistanceFromOrigin(point);
                double dAngle{ 0.0 };
                for (int nRing = 1; nRing <= TotalRings; ++nRing)
                {
                    if (abs(dDistance - m_analyticalRings[nRing].dRadius) < 3 )
                    {
                        dAngle = atan2((resultRings[0][0].center.m_dY - point.m_dY), (point.m_dX - resultRings[0][0].center.m_dX));
                        // Convert angle to range [0 : 2 PI]
                        dAngle = (dAngle < 0) ? (2 * M_PI + dAngle) : dAngle;
                        return make_tuple(nRing, dAngle);
                    }
                }
                return make_tuple(InvalidRingNo, dAngle);
            };

Does this answer your question? https://stackoverflow.com/questions/34510/what-is-a-race-condition — 463035818_is_not_an_ai, Nov 30 '20 at 10:52
i doubt you can find something that explicity states your code is ok. You can find rules for what is not ok, and they do not apply because nothing is written — 463035818_is_not_an_ai, Nov 30 '20 at 10:53
My question is whether I have to protect the method GroupCirclesByRing with a mutex — Maanu, Nov 30 '20 at 10:56
I understand what your question is. You need a mutex to protect from race conditions. Did you read the above link? — 463035818_is_not_an_ai, Nov 30 '20 at 10:57
btw details do matter. It is possible to add code to your 2 lines that make them do something entirely different and actually modify the vector. Please include a [mcve] if you want to be sure that you get correct answers — 463035818_is_not_an_ai, Nov 30 '20 at 10:58

score 0 · Answer 1 · answered Nov 30 '20 at 11:12

0

Where can I find the documentation to ensure that thread synchronization is not required?

That would be the C++ standard. Drafts are publicly available at https://github.com/cplusplus/draft

Take a look at sections like [intro.races].

answered Nov 30 '20 at 11:12

Acorn

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Vector [] operation (read only) thread safety

1 Answers1