SIMD & Vectorization Execution Policy for for_each (C++ 17)
std::execution::par_unseq is an execution policy introduced in C++17 that you can pass to algorithms like std::for_each. It directs the algorithm to execute in parallel and in an unordered fashion, allowing the implementation to use both multi-threading and vectorization (SIMD). This means that iterations may be run concurrently without any guarantee of order, so you must ensure that your loop body is free of data races and side effects that depend on ordering.
- Note: different execution policies have their own types. So:
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// We have to use an if-else because the parallelism_policy are different types
// auto parallelism_policy = parallel ? std::execution::par_unseq : std::execution::seq;
if (parallel) {
std::for_each(std::execution::seq, matches.begin(), matches.end(),
[idx = 0](NNMatch& match) mutable {
match.idx_in_this_cloud = idx++;
});
} else {
}
