| // Copyright 2016 The Netstack Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| // Package ilist provides the implementation of intrusive linked lists. |
| package ilist |
| |
| // Linker is the interface that objects must implement if they want to be added |
| // to and/or removed from List objects. |
| // |
| // N.B. When substituted in a template instantiation, Linker doesn't need to |
| // be an interface, and in most cases won't be. |
| type Linker interface { |
| Next() Linker |
| Prev() Linker |
| SetNext(Linker) |
| SetPrev(Linker) |
| } |
| |
| // List is an intrusive list. Entries can be added to or removed from the list |
| // in O(1) time and with no additional memory allocations. |
| // |
| // The zero value for List is an empty list ready to use. |
| // |
| // To iterate over a list (where l is a List): |
| // for e := l.Front(); e != nil; e = e.Next() { |
| // // do something with e. |
| // } |
| type List struct { |
| head Linker |
| tail Linker |
| } |
| |
| // Reset resets list l to the empty state. |
| func (l *List) Reset() { |
| l.head = nil |
| l.tail = nil |
| } |
| |
| // Empty returns true iff the list is empty. |
| func (l *List) Empty() bool { |
| return l.head == nil |
| } |
| |
| // Front returns the first element of list l or nil. |
| func (l *List) Front() Linker { |
| return l.head |
| } |
| |
| // Back returns the last element of list l or nil. |
| func (l *List) Back() Linker { |
| return l.tail |
| } |
| |
| // PushFront inserts the element e at the front of list l. |
| func (l *List) PushFront(e Linker) { |
| e.SetNext(l.head) |
| e.SetPrev(nil) |
| |
| if l.head != nil { |
| l.head.SetPrev(e) |
| } else { |
| l.tail = e |
| } |
| |
| l.head = e |
| } |
| |
| // PushBack inserts the element e at the back of list l. |
| func (l *List) PushBack(e Linker) { |
| e.SetNext(nil) |
| e.SetPrev(l.tail) |
| |
| if l.tail != nil { |
| l.tail.SetNext(e) |
| } else { |
| l.head = e |
| } |
| |
| l.tail = e |
| } |
| |
| // PushBackList inserts list m at the end of list l, emptying m. |
| func (l *List) PushBackList(m *List) { |
| if l.head == nil { |
| l.head = m.head |
| l.tail = m.tail |
| } else if m.head != nil { |
| l.tail.SetNext(m.head) |
| m.head.SetPrev(l.tail) |
| |
| l.tail = m.tail |
| } |
| |
| m.head = nil |
| m.tail = nil |
| } |
| |
| // InsertAfter inserts e after b. |
| func (l *List) InsertAfter(b, e Linker) { |
| a := b.Next() |
| e.SetNext(a) |
| e.SetPrev(b) |
| b.SetNext(e) |
| |
| if a != nil { |
| a.SetPrev(e) |
| } else { |
| l.tail = e |
| } |
| } |
| |
| // InsertBefore inserts e before a. |
| func (l *List) InsertBefore(a, e Linker) { |
| b := a.Prev() |
| e.SetNext(a) |
| e.SetPrev(b) |
| a.SetPrev(e) |
| |
| if b != nil { |
| b.SetNext(e) |
| } else { |
| l.head = e |
| } |
| } |
| |
| // Remove removes e from l. |
| func (l *List) Remove(e Linker) { |
| prev := e.Prev() |
| next := e.Next() |
| |
| if prev != nil { |
| prev.SetNext(next) |
| } else { |
| l.head = next |
| } |
| |
| if next != nil { |
| next.SetPrev(prev) |
| } else { |
| l.tail = prev |
| } |
| } |
| |
| // Entry is a default implementation of Linker. Users can add anonymous fields |
| // of this type to their structs to make them automatically implement the |
| // methods needed by List. |
| type Entry struct { |
| next Linker |
| prev Linker |
| } |
| |
| // Next returns the entry that follows e in the list. |
| func (e *Entry) Next() Linker { |
| return e.next |
| } |
| |
| // Prev returns the entry that precedes e in the list. |
| func (e *Entry) Prev() Linker { |
| return e.prev |
| } |
| |
| // SetNext assigns 'entry' as the entry that follows e in the list. |
| func (e *Entry) SetNext(entry Linker) { |
| e.next = entry |
| } |
| |
| // SetPrev assigns 'entry' as the entry that precedes e in the list. |
| func (e *Entry) SetPrev(entry Linker) { |
| e.prev = entry |
| } |