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AK: Avoid allocations for the Queue class

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Previously the Queue class used a SinglyLinkedList to manage its queue
segments. This changes the Queue class to use the IntrusiveList class
instead which saves us one allocation per segment.
This commit is contained in:
Gunnar Beutner 2021-05-22 16:17:32 +02:00 committed by Andreas Kling
parent 859e5741ff
commit 3ff0a3aa4b
1 changed files with 22 additions and 9 deletions
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31
AK/Queue.h
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@ -6,6 +6,7 @@
#pragma once
#include <AK/IntrusiveList.h>
#include <AK/OwnPtr.h>
#include <AK/SinglyLinkedList.h>
#include <AK/Vector.h>
@ -16,7 +17,11 @@ template<typename T, int segment_size = 1000>
class Queue {
public:
Queue() = default;
~Queue() = default;
~Queue()
{
clear();
}
size_t size() const { return m_size; }
bool is_empty() const { return m_size == 0; }
@ -24,18 +29,20 @@ public:
template<typename U = T>
void enqueue(U&& value)
{
if (m_segments.is_empty() || m_segments.last()->size() >= segment_size)
m_segments.append(make<Vector<T, segment_size>>());
m_segments.last()->append(forward<U>(value));
if (m_segments.is_empty() || m_segments.last()->data.size() >= segment_size) {
auto segment = new QueueSegment;
m_segments.append(*segment);
}
m_segments.last()->data.append(forward<U>(value));
++m_size;
}
T dequeue()
{
VERIFY(!is_empty());
auto value = move((*m_segments.first())[m_index_into_first++]);
auto value = move(m_segments.first()->data[m_index_into_first++]);
if (m_index_into_first == segment_size) {
m_segments.take_first();
delete m_segments.take_first();
m_index_into_first = 0;
}
--m_size;
@ -45,18 +52,24 @@ public:
const T& head() const
{
VERIFY(!is_empty());
return (*m_segments.first())[m_index_into_first];
return m_segments.first()->data[m_index_into_first];
}
void clear()
{
m_segments.clear();
while (auto* segment = m_segments.take_first())
delete segment;
m_index_into_first = 0;
m_size = 0;
}
private:
SinglyLinkedList<OwnPtr<Vector<T, segment_size>>> m_segments;
struct QueueSegment {
Vector<T, segment_size> data;
IntrusiveListNode<QueueSegment> node;
};
IntrusiveList<QueueSegment, RawPtr<QueueSegment>, &QueueSegment::node> m_segments;
size_t m_index_into_first { 0 };
size_t m_size { 0 };
};