60 lines
1.5 KiB
C++
60 lines
1.5 KiB
C++
#include <atomic>
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template<typename T>
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class lock_free_queue
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{
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private:
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struct node;
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struct counted_node_ptr
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{
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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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{
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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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{
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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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{
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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(
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old_data,new_data.get()))
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{
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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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