add original source

source/listing_7.15.cpp

@@ -0,0 +1,59 @@
+#include <atomic>
+
+template<typename T>
+class lock_free_queue
+{
+private:
+    struct node;
+    struct counted_node_ptr
+    {
+        int external_count;
+        node* ptr;
+    };
+    std::atomic<counted_node_ptr> head;
+    std::atomic<counted_node_ptr> tail;
+    struct node_counter
+    {
+        unsigned internal_count:30;
+        unsigned external_counters:2;
+    };
+    struct node
+    {
+        std::atomic<T*> data;
+        std::atomic<node_counter> count;
+        counted_node_ptr next;
+        node()
+        {
+            node_counter new_count;
+            new_count.internal_count=0;
+            new_count.external_counters=2;
+            count.store(new_count);
+            next.ptr=nullptr;
+            next.external_count=0;
+        }
+    };
+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()))
+            {
+                old_tail.ptr->next=new_next;
+                old_tail=tail.exchange(new_next);
+                free_external_counter(old_tail);
+                new_data.release();
+                break;
+            }
+            old_tail.ptr->release_ref();
+        }
+    }
+};