add original source

source/listing_7.21.cpp

@@ -0,0 +1,55 @@
+template<typename T>
+class lock_free_queue
+{
+private:
+    void set_new_tail(counted_node_ptr &old_tail,
+                      counted_node_ptr const &new_tail)
+    {
+        node* const current_tail_ptr=old_tail.ptr;
+        while(!tail.compare_exchange_weak(old_tail,new_tail) &&
+              old_tail.ptr==current_tail_ptr);
+        if(old_tail.ptr==current_tail_ptr)
+            free_external_counter(old_tail);
+        else
+            current_tail_ptr->release_ref();
+    }
+public:
+    void push(T new_value)
+    {
+        std::unique_ptr<T> new_data(new T(new_value));
+        counted_node_ptr new_next;
+        new_next.ptr=new node;
+        new_next.external_count=1;
+        counted_node_ptr old_tail=tail.load();
+        for(;;)
+        {
+            increase_external_count(tail,old_tail);
+            T* old_data=nullptr;
+            if(old_tail.ptr->data.compare_exchange_strong(
+                   old_data,new_data.get()))
+            {
+                counted_node_ptr old_next={0};
+                if(!old_tail.ptr->next.compare_exchange_strong(
+                       old_next,new_next))
+                {
+                    delete new_next.ptr;
+                    new_next=old_next;
+                }
+                set_new_tail(old_tail, new_next);
+                new_data.release();
+                break;
+            }
+            else
+            {
+                counted_node_ptr old_next={0};
+                if(old_tail.ptr->next.compare_exchange_strong(
+                       old_next,new_next))
+                {
+                    old_next=new_next;
+                    new_next.ptr=new node;
+                }
+                set_new_tail(old_tail, old_next);
+            }
+        }
+    }
+};