Lets add another intrusive double linked list!

Features:
* STL-like interface
* Fast modification: no branches on insertion or deletion
* Fast iteration: one pointer dereference and one pointer comparison
* Your class can be a part of several lists

Modeled after std::list<T> but currently has fewer methods (not complete yet)

For even more performance it's possible to customize list with templates so
it won't have size counter variable or won't NULLify unlinked node.

How existing lists differ?

No existing lists support STL-like interface.

I_List:
* slower iteration (one more branch on iteration)
* element can't be a part of two lists simultaneously

I_P_List:
* slower modification (branches, except for the fastest push_back() case)
* slower iteration (one more branch on iteration)

UT_LIST_BASE_NODE_T:
* slower modification (branches)

Three UT_LISTs were replaced: two in fil_system_t and one in dyn_buf_t.

1 files changed, 188 insertions, 0 deletions

diff --git a/include/intrusive_list.h b/include/intrusive_list.h
new file mode 100644
index 00000000000..23534596b93
--- /dev/null
+++ b/include/intrusive_list.h
@@ -0,0 +1,188 @@
+/*
+   Copyright (c) 2019, 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 const Iterator const_iterator;
+  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(); }
+
+  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