55 lines
1.3 KiB
C++
55 lines
1.3 KiB
C++
#include <atomic>
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template <typename T>
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class lock_free_queue {
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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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std::atomic<counted_node_ptr> head;
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std::atomic<counted_node_ptr> tail;
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struct node_counter {
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unsigned internal_count : 30;
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unsigned external_counters : 2;
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};
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struct node {
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std::atomic<T*> data;
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std::atomic<node_counter> count;
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counted_node_ptr next;
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node()
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{
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node_counter new_count;
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new_count.internal_count = 0;
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new_count.external_counters = 2;
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count.store(new_count);
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next.ptr = nullptr;
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next.external_count = 0;
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}
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};
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public:
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void push(T new_value)
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{
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std::unique_ptr<T> new_data(new T(new_value));
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counted_node_ptr new_next;
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new_next.ptr = new node;
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new_next.external_count = 1;
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counted_node_ptr old_tail = tail.load();
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for (;;) {
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increase_external_count(tail, old_tail);
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T* old_data = nullptr;
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if (old_tail.ptr->data.compare_exchange_strong(old_data,
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new_data.get())) {
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old_tail.ptr->next = new_next;
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old_tail = tail.exchange(new_next);
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free_external_counter(old_tail);
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new_data.release();
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break;
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}
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old_tail.ptr->release_ref();
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}
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}
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};
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