24 Containers library [containers]

24.2 Requirements [container.requirements]

24.2.3 Container data races [container.requirements.dataraces]

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For purposes of avoiding data races ([res.on.data.races]), implementations shall consider the following functions to be const: begin, end, rbegin, rend, front, back, data, find, lower_bound, upper_bound, equal_range, at and, except in associative or unordered associative containers, operator[].
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Notwithstanding [res.on.data.races], implementations are required to avoid data races when the contents of the contained object in different elements in the same container, excepting vector<bool>, are modified concurrently.
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[Note 1: 
For a vector<int> x with a size greater than one, x[1] = 5 and *x.begin() = 10 can be executed concurrently without a data race, but x[0] = 5 and *x.begin() = 10 executed concurrently can result in a data race.
As an exception to the general rule, for a vector<bool> y, y[0] = true can race with y[1] = true.
— end note]