1 files changed, 190 insertions, 0 deletions
diff --git a/include/intrusive_list.h b/include/intrusive_list.h
new file mode 100644
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+++ b/include/intrusive_list.h
@@ -0,0 +1,190 @@
+/*
+   Copyright (c) 2019, 2020, MariaDB
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License
+   as published by the Free Software Foundation; version 2 of
+   the License.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335  USA
+*/
+
+#pragma once
+
+#include <cstddef>
+#include <iterator>
+
+namespace intrusive
+{
+
+// Derive your class from this struct to insert to a linked list.
+template <class Tag= void> struct list_node
+{
+  list_node(list_node *next= NULL, list_node *prev= NULL)
+      : next(next), prev(prev)
+  {
+  }
+
+  list_node *next;
+  list_node *prev;
+};
+
+// Modelled after std::list<T>
+template <class T, class Tag= void> class list
+{
+public:
+  typedef list_node<Tag> ListNode;
+  class Iterator;
+
+  // All containers in C++ should define these types to implement generic
+  // container interface.
+  typedef T value_type;
+  typedef std::size_t size_type;
+  typedef std::ptrdiff_t difference_type;
+  typedef value_type &reference;
+  typedef const value_type &const_reference;
+  typedef T *pointer;
+  typedef const T *const_pointer;
+  typedef Iterator iterator;
+  typedef Iterator const_iterator; /* FIXME */
+  typedef std::reverse_iterator<iterator> reverse_iterator;
+  typedef std::reverse_iterator<const iterator> const_reverse_iterator;
+
+  class Iterator
+  {
+  public:
+    // All iterators in C++ should define these types to implement generic
+    // iterator interface.
+    typedef std::bidirectional_iterator_tag iterator_category;
+    typedef T value_type;
+    typedef std::ptrdiff_t difference_type;
+    typedef T *pointer;
+    typedef T &reference;
+
+    Iterator(ListNode *node) : node_(node) {}
+
+    Iterator &operator++()
+    {
+      node_= node_->next;
+      return *this;
+    }
+    Iterator operator++(int)
+    {
+      Iterator tmp(*this);
+      operator++();
+      return tmp;
+    }
+
+    Iterator &operator--()
+    {
+      node_= node_->prev;
+      return *this;
+    }
+    Iterator operator--(int)
+    {
+      Iterator tmp(*this);
+      operator--();
+      return tmp;
+    }
+
+    reference operator*() { return *static_cast<pointer>(node_); }
+    pointer operator->() { return static_cast<pointer>(node_); }
+
+    bool operator==(const Iterator &rhs) { return node_ == rhs.node_; }
+    bool operator!=(const Iterator &rhs) { return !(*this == rhs); }
+
+  private:
+    ListNode *node_;
+
+    friend class list;
+  };
+
+  list() : sentinel_(&sentinel_, &sentinel_), size_(0) {}
+
+  reference front() { return *begin(); }
+  reference back() { return *--end(); }
+  const_reference front() const { return *begin(); }
+  const_reference back() const { return *--end(); }
+
+  iterator begin() { return iterator(sentinel_.next); }
+  const_iterator begin() const
+  {
+    return iterator(const_cast<ListNode *>(sentinel_.next));
+  }
+  iterator end() { return iterator(&sentinel_); }
+  const_iterator end() const
+  {
+    return iterator(const_cast<ListNode *>(&sentinel_));
+  }
+
+  reverse_iterator rbegin() { return reverse_iterator(end()); }
+  const_reverse_iterator rbegin() const { return reverse_iterator(end()); }
+  reverse_iterator rend() { return reverse_iterator(begin()); }
+  const_reverse_iterator rend() const { return reverse_iterator(begin()); }
+
+  bool empty() const { return size_ == 0; }
+  size_type size() const { return size_; }
+
+  void clear()
+  {
+    sentinel_.next= &sentinel_;
+    sentinel_.prev= &sentinel_;
+    size_= 0;
+  }
+
+  iterator insert(iterator pos, reference value)
+  {
+    ListNode *curr= pos.node_;
+    ListNode *prev= pos.node_->prev;
+
+    prev->next= &value;
+    curr->prev= &value;
+
+    static_cast<ListNode &>(value).prev= prev;
+    static_cast<ListNode &>(value).next= curr;
+
+    ++size_;
+    return iterator(&value);
+  }
+
+  iterator erase(iterator pos)
+  {
+    ListNode *prev= pos.node_->prev;
+    ListNode *next= pos.node_->next;
+
+    prev->next= next;
+    next->prev= prev;
+
+    // This is not required for list functioning. But maybe it'll prevent bugs
+    // and ease debugging.
+    ListNode *curr= pos.node_;
+    curr->prev= NULL;
+    curr->next= NULL;
+
+    --size_;
+    return next;
+  }
+
+  void push_back(reference value) { insert(end(), value); }
+  void pop_back() { erase(end()); }
+
+  void push_front(reference value) { insert(begin(), value); }
+  void pop_front() { erase(begin()); }
+
+  // STL version is O(n) but this is O(1) because an element can't be inserted
+  // several times in the same intrusive list.
+  void remove(reference value) { erase(iterator(&value)); }
+
+private:
+  ListNode sentinel_;
+  size_type size_;
+};
+
+} // namespace intrusive