89 lines
2.5 KiB
C++
89 lines
2.5 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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{
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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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struct node
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{
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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_):
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data(std::make_shared<T>(data_)),
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internal_count(0)
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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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{
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new_counter=old_counter;
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++new_counter.external_count;
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}
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while(!head.compare_exchange_strong(
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old_counter,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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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)
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while(!head.compare_exchange_weak(
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new_node.ptr->next,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=
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head.load(std::memory_order_relaxed);
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for(;;)
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{
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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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{
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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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{
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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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{
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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(
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-1,std::memory_order_relaxed)==1)
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{
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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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