[http_server] Cache parameter child pointer for O(1) lookup fallback - #4
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cong1920 wants to merge 1 commit into
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[http_server] Cache parameter child pointer for O(1) lookup fallback#4cong1920 wants to merge 1 commit into
cong1920 wants to merge 1 commit into
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In find(), when a static child lookup misses, the code previously did a
linear scan of ALL children to find a {{param}} child. This is O(n) per
tree level for every parameterized route lookup.
Fix: Cache param_child_ pointer during find_or_create(), so find() can
fall back to it in O(1) instead of scanning.
Benchmark results (median, 25 iterations, WSL2 g++ -O2):
Before After Change
insert: 313.3 ns/op 299.2 ns/op -4.5%
lookup hit: 80.7 ns/op 72.7 ns/op -9.9%
lookup miss: 45.0 ns/op 36.6 ns/op -18.7%
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Committed directly to simplify_drt_node instead. |
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Summary
Cache the {{param}} child pointer during route registration ( ind_or_create) so that ind() can fall back to it in O(1) instead of doing a linear scan of all children.
Problem
In ind(), when a static child lookup misses, the code did a linear scan of ALL children to find a {{param}} child:
\\cpp
for (const auto& kv : children_) {
if (name.size() > 4 and name[0] == '{' and name[1] == '{' ...)
return kv.second->find(r, c);
}
\\
This is O(n) per tree level for every parameterized route lookup.
Fix
Added a cached pointer set during \ ind_or_create():
\\cpp
drt_node* param_child_ = nullptr;
\\
Now \ ind()\ falls back in O(1):
\\cpp
if (param_child_)
return param_child_->find(r, c);
return end();
\\
Benchmark Results
Environment: WSL2 Ubuntu, g++ -O2 -std=c++20, 25 iterations
vs master branch
The hot path (lookups) now beats master by 10-20%.