79 lines
2.2 KiB
C++
79 lines
2.2 KiB
C++
#include <atomic>
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#include <memory>
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template <typename T>
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class lock_free_stack {
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private:
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struct node;
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struct counted_node_ptr {
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int external_count;
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node* ptr;
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};
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struct node {
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std::shared_ptr<T> data;
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std::atomic<int> internal_count;
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counted_node_ptr next;
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node(T const& data_) : data(std::make_shared<T>(data_)), internal_count(0)
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{
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}
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};
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std::atomic<counted_node_ptr> head;
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void increase_head_count(counted_node_ptr& old_counter)
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{
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counted_node_ptr new_counter;
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do {
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new_counter = old_counter;
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++new_counter.external_count;
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} while (!head.compare_exchange_strong(old_counter,
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new_counter,
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std::memory_order_acquire,
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std::memory_order_relaxed));
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old_counter.external_count = new_counter.external_count;
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}
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public:
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~lock_free_stack()
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{
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while (pop())
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;
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}
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void push(T const& data)
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{
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counted_node_ptr new_node;
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new_node.ptr = new node(data);
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new_node.external_count = 1;
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new_node.ptr->next = head.load(std::memory_order_relaxed) while (
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!head.compare_exchange_weak(new_node.ptr->next,
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new_node,
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std::memory_order_release,
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std::memory_order_relaxed));
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}
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std::shared_ptr<T> pop()
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{
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counted_node_ptr old_head = head.load(std::memory_order_relaxed);
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for (;;) {
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increase_head_count(old_head);
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node* const ptr = old_head.ptr;
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if (!ptr) {
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return std::shared_ptr<T>();
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}
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if (head.compare_exchange_strong(
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old_head, ptr->next, std::memory_order_relaxed)) {
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std::shared_ptr<T> res;
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res.swap(ptr->data);
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int const count_increase = old_head.external_count - 2;
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if (ptr->internal_count.fetch_add(
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count_increase, std::memory_order_release) == -count_increase) {
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delete ptr;
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}
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return res;
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}
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else if (ptr->internal_count.fetch_add(-1, std::memory_order_relaxed) ==
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1) {
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ptr->internal_count.load(std::memory_order_acquire);
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delete ptr;
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}
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}
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}
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};
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