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Simplify clear() and avoid iterating when values have trivial destructor.

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Resolves #205.
This commit is contained in:
greg7mdp
2023-09-02 14:47:18 -04:00
parent df7935aca3
commit 38ded9bba8
1 changed files with 16 additions and 17 deletions
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parallel_hashmap/phmap.h
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+16 -17
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@@ -1268,21 +1268,15 @@ public:
size_t max_size() const { return (std::numeric_limits<size_t>::max)(); }
PHMAP_ATTRIBUTE_REINITIALIZES void clear() {
// Iterating over this container is O(bucket_count()). When bucket_count()
// is much greater than size(), iteration becomes prohibitively expensive.
// For clear() it is more important to reuse the allocated array when the
// container is small because allocation takes comparatively long time
// compared to destruction of the elements of the container. So we pick the
// largest bucket_count() threshold for which iteration is still fast and
// past that we simply deallocate the array.
if (empty())
return;
if (capacity_ > 127) {
destroy_slots();
} else if (capacity_) {
for (size_t i = 0; i != capacity_; ++i) {
if (IsFull(ctrl_[i])) {
PolicyTraits::destroy(&alloc_ref(), slots_ + i);
if (capacity_) {
if constexpr (!std::is_trivially_destructible<typename PolicyTraits::value_type>::value) {
// not trivially destructible... we need to iterate and destroy values one by one
for (size_t i = 0; i != capacity_; ++i) {
if (IsFull(ctrl_[i])) {
PolicyTraits::destroy(&alloc_ref(), slots_ + i);
}
}
}
size_ = 0;
@@ -2011,10 +2005,15 @@ private:
}
void destroy_slots() {
if (!capacity_) return;
for (size_t i = 0; i != capacity_; ++i) {
if (IsFull(ctrl_[i])) {
PolicyTraits::destroy(&alloc_ref(), slots_ + i);
if (!capacity_)
return;
if constexpr (!std::is_trivially_destructible<typename PolicyTraits::value_type>::value) {
// not trivially destructible... we need to iterate and destroy values one by one
for (size_t i = 0; i != capacity_; ++i) {
if (IsFull(ctrl_[i])) {
PolicyTraits::destroy(&alloc_ref(), slots_ + i);
}
}
}
auto layout = MakeLayout(capacity_);