[09_queue] concurrency, lock_free_queue, done.

c-cpp/09_queue/lock_free_queue.hpp

@@ -0,0 +1,74 @@
+/**
+ * Created by Liam Huang (Liam0205) on 2018/10/11.
+ */
+
+#ifndef QUEUE_LOCK_FREE_QUEUE_HPP_
+#define QUEUE_LOCK_FREE_QUEUE_HPP_
+
+#include <memory>
+#include <atomic>
+
+template <typename T>
+class LockFreeQueue {
+  public:
+    using value_type      = T;
+
+  private:
+    struct node {
+        std::shared<value_type> data = nullptr;
+        node* next                   = nullptr;
+    };
+    std::atomic<node*> head = nullptr;
+    std::atomic<node*> tail = nullptr;
+
+  public:
+    LockFreeQueue() head(new node), tail(head.load()) {}
+    LockFreeQueue(const LockFreeQueue&) = delete;
+    LockFreeQueue& operator=(const LockFreeQueue&) = delete;
+    // TODO(Liam Huang): move constructor and move assignment should be well implemented later,
+    //                   and hance marked "delete".
+    LockFreeQueue(LockFreeQueue&&) = delete;
+    LockFreeQueue& operator=(LockFreeQueue&&) = delete;
+    ~LockFreeQueue() {
+        while (node* const old_head = head.load()) {
+            head.store(old_head->next);
+            delete old_head;
+        }
+    }
+
+  private:
+    node* pop_head() {
+        node* const res = head.load();
+        if (res == tail.load()) {
+            return nullptr;
+        }
+        head.store(res->next);
+        return res;
+    }
+
+  public:
+    bool empty() const {
+        return head.load() == tail.load();
+    }
+    std::shared_ptr<value_type> pop() {
+        node* old_head = pop_head();
+        if (nullptr == old_head) {
+            return nullptr;
+        } else {
+            auto res = old_head->data;
+            delete old_head;
+            return res;
+        }
+    }
+    void push(value_type new_value) {
+        auto new_data = std::make_shared<value_type>(new_value);
+        node* p = new node;
+        node* old_tail = tail.load();
+        old_tail->data.swap(new_data);
+        old_tail->next = p;
+        tail_.store(p);
+    }
+};
+
+#endif  // QUEUE_LOCK_FREE_QUEUE_HPP_
+