Extra helper functions for dllist (#139)

* More helpful functions for dllist

src/ds/dllist.h

@@ -53,8 +53,11 @@ namespace snmalloc
     }
   };
 
-  template<class T, class Terminator = std::nullptr_t>
-  class DLList
+  template<
+    class T,
+    class Terminator = std::nullptr_t,
+    bool delete_on_clear = false>
+  class DLList final
   {
   private:
     static_assert(
@@ -66,6 +69,32 @@ namespace snmalloc
     T* tail = Terminator();
 
   public:
+    ~DLList()
+    {
+      clear();
+    }
+
+    DLList() = default;
+
+    DLList(DLList&& o) noexcept
+    {
+      head = o.head;
+      tail = o.tail;
+
+      o.head = nullptr;
+      o.tail = nullptr;
+    }
+
+    DLList& operator=(DLList&& o) noexcept
+    {
+      head = o.head;
+      tail = o.tail;
+
+      o.head = nullptr;
+      o.tail = nullptr;
+      return *this;
+    }
+
     bool is_empty()
     {
       return head == Terminator();
@@ -76,6 +105,11 @@ namespace snmalloc
       return head;
     }
 
+    T* get_tail()
+    {
+      return tail;
+    }
+
     T* pop()
     {
       T* item = head;
@@ -86,6 +120,16 @@ namespace snmalloc
       return item;
     }
 
+    T* pop_tail()
+    {
+      T* item = tail;
+
+      if (item != Terminator())
+        remove(item);
+
+      return item;
+    }
+
     void insert(T* item)
     {
 #ifndef NDEBUG
@@ -147,6 +191,19 @@ namespace snmalloc
 #endif
     }
 
+    void clear()
+    {
+      while (head != nullptr)
+      {
+        auto c = head;
+        remove(c);
+        if (delete_on_clear)
+        {
+          delete c;
+        }
+      }
+    }
+
     void debug_check_contains(T* item)
     {
 #ifndef NDEBUG