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package futex
// ElementMapper provides an identity mapping by default.
//
// This can be replaced to provide a struct that maps elements to linker
// objects, if they are not the same. An ElementMapper is not typically
// required if: Linker is left as is, Element is left as is, or Linker and
// Element are the same type.
type waiterElementMapper struct{}
// linkerFor maps an Element to a Linker.
//
// This default implementation should be inlined.
//
//go:nosplit
func (waiterElementMapper) linkerFor(elem *Waiter) *Waiter { return elem }
// 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.
// }
//
// +stateify savable
type waiterList struct {
head *Waiter
tail *Waiter
}
// Reset resets list l to the empty state.
func (l *waiterList) Reset() {
l.head = nil
l.tail = nil
}
// Empty returns true iff the list is empty.
func (l *waiterList) Empty() bool {
return l.head == nil
}
// Front returns the first element of list l or nil.
func (l *waiterList) Front() *Waiter {
return l.head
}
// Back returns the last element of list l or nil.
func (l *waiterList) Back() *Waiter {
return l.tail
}
// PushFront inserts the element e at the front of list l.
func (l *waiterList) PushFront(e *Waiter) {
linker := waiterElementMapper{}.linkerFor(e)
linker.SetNext(l.head)
linker.SetPrev(nil)
if l.head != nil {
waiterElementMapper{}.linkerFor(l.head).SetPrev(e)
} else {
l.tail = e
}
l.head = e
}
// PushBack inserts the element e at the back of list l.
func (l *waiterList) PushBack(e *Waiter) {
linker := waiterElementMapper{}.linkerFor(e)
linker.SetNext(nil)
linker.SetPrev(l.tail)
if l.tail != nil {
waiterElementMapper{}.linkerFor(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 *waiterList) PushBackList(m *waiterList) {
if l.head == nil {
l.head = m.head
l.tail = m.tail
} else if m.head != nil {
waiterElementMapper{}.linkerFor(l.tail).SetNext(m.head)
waiterElementMapper{}.linkerFor(m.head).SetPrev(l.tail)
l.tail = m.tail
}
m.head = nil
m.tail = nil
}
// InsertAfter inserts e after b.
func (l *waiterList) InsertAfter(b, e *Waiter) {
bLinker := waiterElementMapper{}.linkerFor(b)
eLinker := waiterElementMapper{}.linkerFor(e)
a := bLinker.Next()
eLinker.SetNext(a)
eLinker.SetPrev(b)
bLinker.SetNext(e)
if a != nil {
waiterElementMapper{}.linkerFor(a).SetPrev(e)
} else {
l.tail = e
}
}
// InsertBefore inserts e before a.
func (l *waiterList) InsertBefore(a, e *Waiter) {
aLinker := waiterElementMapper{}.linkerFor(a)
eLinker := waiterElementMapper{}.linkerFor(e)
b := aLinker.Prev()
eLinker.SetNext(a)
eLinker.SetPrev(b)
aLinker.SetPrev(e)
if b != nil {
waiterElementMapper{}.linkerFor(b).SetNext(e)
} else {
l.head = e
}
}
// Remove removes e from l.
func (l *waiterList) Remove(e *Waiter) {
prev := waiterElementMapper{}.linkerFor(e).Prev()
next := waiterElementMapper{}.linkerFor(e).Next()
if prev != nil {
waiterElementMapper{}.linkerFor(prev).SetNext(next)
} else {
l.head = next
}
if next != nil {
waiterElementMapper{}.linkerFor(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.
//
// +stateify savable
type waiterEntry struct {
next *Waiter
prev *Waiter
}
// Next returns the entry that follows e in the list.
func (e *waiterEntry) Next() *Waiter {
return e.next
}
// Prev returns the entry that precedes e in the list.
func (e *waiterEntry) Prev() *Waiter {
return e.prev
}
// SetNext assigns 'entry' as the entry that follows e in the list.
func (e *waiterEntry) SetNext(elem *Waiter) {
e.next = elem
}
// SetPrev assigns 'entry' as the entry that precedes e in the list.
func (e *waiterEntry) SetPrev(elem *Waiter) {
e.prev = elem
}
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