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Eliminate literals passed to device_uvector::set_element_async #367

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merged 2 commits into from
Mar 18, 2021
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Eliminate literals passed to device_uvector::set_element_async #367

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a1e9c50
Eliminate literals passed to device_uvector::set_element_async
harrism Mar 10, 2021
40396c7
Merge branch 'branch-0.19' into fix-async-set-value-literal
harrism Mar 16, 2021
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3 changes: 2 additions & 1 deletion cpp/src/join/detail/traversal.cuh
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Original file line number Diff line number Diff line change
Expand Up @@ -72,7 +72,8 @@ descend_quadtree(LengthsIter counts,
thrust::inclusive_scan(
rmm::exec_policy(stream), parent_counts, parent_counts + num_quads, parent_offsets.begin() + 1);

parent_offsets.set_element_async(0, 0, stream);
uint32_t init{0};
parent_offsets.set_element_async(0, init, stream);
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Why eliminate one 0 literal and not the other?

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Great question. Only the value parameter (second parameter) is pass-by-reference, so that's the only one we are disallowing to be a literal. The first parameter, the index, is pass-by-value so it's perfectly safe to use a literal since it will be copied rather than referenced, and so we don't have to worry about the lifetime of the temporary inside set_element_async.

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@thomcom thomcom Mar 18, 2021 •
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That answers my question, yes. But why have one argument be pass by reference and one pass by value? They're both primitives. The 0 is only going to be used by the callee, and the init is going to be passed around and modified by others but has to be initialized here? Thanks!


auto num_children = parent_offsets.back_element(stream); // synchronizes stream

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3 changes: 2 additions & 1 deletion cpp/src/join/quadtree_point_in_polygon.cu
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Expand Up @@ -134,7 +134,8 @@ struct compute_quadtree_point_in_polygon {
local_point_offsets.begin() + 1);

// Ensure local point offsets starts at 0
local_point_offsets.set_element_async(0, 0, stream);
uint32_t init{0};
local_point_offsets.set_element_async(0, init, stream);

// The last element is the total number of points to test against any polygon.
auto num_total_points = local_point_offsets.back_element(stream);
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