Remove CList, moved to go-clist

9 years ago · dbd04eadeb
--- a/clist.go
+++ b/clist.go
@ -1,279 +0,0 @@
 package common

 /*
 The purpose of CList is to provide a goroutine-safe linked-list.
 This list can be traversed concurrently by any number of goroutines.
 However, removed CElements cannot be added back.
 NOTE: Not all methods of container/list are (yet) implemented.
 NOTE: Removed elements need to NukePrev or NukeNext consistently
 to ensure garbage collection of removed elements.
 */

 import (
 	"sync"
 	"sync/atomic"
 	"unsafe"
 )

 // CElement is an element of a linked-list
 // Traversal from a CElement are goroutine-safe.
 type CElement struct {
 	next    unsafe.Pointer
 	nextWg  *sync.WaitGroup
 	prev    unsafe.Pointer
 	prevWg  *sync.WaitGroup
 	removed uint32
 	Value   interface{}
 }

 // Blocking implementation of Next().
 // May return nil iff CElement was tail and got removed.
 func (e *CElement) NextWait() *CElement {
 	for {
 		e.nextWg.Wait()
 		next := e.Next()
 		if next == nil {
 			if e.Removed() {
 				return nil
 			} else {
 				continue
 			}
 		} else {
 			return next
 		}
 	}
 }

 // Blocking implementation of Prev().
 // May return nil iff CElement was head and got removed.
 func (e *CElement) PrevWait() *CElement {
 	for {
 		e.prevWg.Wait()
 		prev := e.Prev()
 		if prev == nil {
 			if e.Removed() {
 				return nil
 			} else {
 				continue
 			}
 		} else {
 			return prev
 		}
 	}
 }

 // Nonblocking, may return nil if at the end.
 func (e *CElement) Next() *CElement {
 	return (*CElement)(atomic.LoadPointer(&e.next))
 }

 // Nonblocking, may return nil if at the end.
 func (e *CElement) Prev() *CElement {
 	return (*CElement)(atomic.LoadPointer(&e.prev))
 }

 func (e *CElement) Removed() bool {
 	return atomic.LoadUint32(&(e.removed)) > 0
 }

 func (e *CElement) DetachNext() {
 	e.setNextAtomic(nil)
 	e.nextWg.Done()
 }

 func (e *CElement) DetachPrev() {
 	e.setPrevAtomic(nil)
 	e.prevWg.Done()
 }

 func (e *CElement) setNextAtomic(next *CElement) {
 	for {
 		oldNext := atomic.LoadPointer(&e.next)
 		if !atomic.CompareAndSwapPointer(&(e.next), oldNext, unsafe.Pointer(next)) {
 			continue
 		}
 		if next == nil && oldNext != nil { // We for-loop in NextWait() so race is ok
 			e.nextWg.Add(1)
 		}
 		if next != nil && oldNext == nil {
 			e.nextWg.Done()
 		}
 		return
 	}
 }

 func (e *CElement) setPrevAtomic(prev *CElement) {
 	for {
 		oldPrev := atomic.LoadPointer(&e.prev)
 		if !atomic.CompareAndSwapPointer(&(e.prev), oldPrev, unsafe.Pointer(prev)) {
 			continue
 		}
 		if prev == nil && oldPrev != nil { // We for-loop in PrevWait() so race is ok
 			e.prevWg.Add(1)
 		}
 		if prev != nil && oldPrev == nil {
 			e.prevWg.Done()
 		}
 		return
 	}
 }

 func (e *CElement) setRemovedAtomic() {
 	atomic.StoreUint32(&(e.removed), 1)
 }

 //--------------------------------------------------------------------------------

 // CList represents a linked list.
 // The zero value for CList is an empty list ready to use.
 // Operations are goroutine-safe.
 type CList struct {
 	mtx  sync.Mutex
 	wg   *sync.WaitGroup
 	head *CElement // first element
 	tail *CElement // last element
 	len  int       // list length
 }

 func (l *CList) Init() *CList {
 	l.mtx.Lock()
 	defer l.mtx.Unlock()
 	l.wg = waitGroup1()
 	l.head = nil
 	l.tail = nil
 	l.len = 0
 	return l
 }

 func NewCList() *CList { return new(CList).Init() }

 func (l *CList) Len() int {
 	l.mtx.Lock()
 	defer l.mtx.Unlock()
 	return l.len
 }

 func (l *CList) Front() *CElement {
 	l.mtx.Lock()
 	defer l.mtx.Unlock()
 	return l.head
 }

 func (l *CList) FrontWait() *CElement {
 	for {
 		l.mtx.Lock()
 		head := l.head
 		wg := l.wg
 		l.mtx.Unlock()
 		if head == nil {
 			wg.Wait()
 		} else {
 			return head
 		}
 	}
 }

 func (l *CList) Back() *CElement {
 	l.mtx.Lock()
 	defer l.mtx.Unlock()
 	return l.tail
 }

 func (l *CList) BackWait() *CElement {
 	for {
 		l.mtx.Lock()
 		tail := l.tail
 		wg := l.wg
 		l.mtx.Unlock()
 		if tail == nil {
 			wg.Wait()
 		} else {
 			return tail
 		}
 	}
 }

 func (l *CList) PushBack(v interface{}) *CElement {
 	l.mtx.Lock()
 	defer l.mtx.Unlock()

 	// Construct a new element
 	e := &CElement{
 		prev:   nil,
 		prevWg: waitGroup1(),
 		next:   nil,
 		nextWg: waitGroup1(),
 		Value:  v,
 	}

 	// Release waiters on FrontWait/BackWait maybe
 	if l.len == 0 {
 		l.wg.Done()
 	}
 	l.len += 1

 	// Modify the tail
 	if l.tail == nil {
 		l.head = e
 		l.tail = e
 	} else {
 		l.tail.setNextAtomic(e)
 		e.setPrevAtomic(l.tail)
 		l.tail = e
 	}

 	return e
 }

 // CONTRACT: Caller must call e.DetachPrev() and/or e.DetachNext() to avoid memory leaks.
 // NOTE: As per the contract of CList, removed elements cannot be added back.
 func (l *CList) Remove(e *CElement) interface{} {
 	l.mtx.Lock()
 	defer l.mtx.Unlock()

 	prev := e.Prev()
 	next := e.Next()

 	if l.head == nil || l.tail == nil {
 		PanicSanity("Remove(e) on empty CList")
 	}
 	if prev == nil && l.head != e {
 		PanicSanity("Remove(e) with false head")
 	}
 	if next == nil && l.tail != e {
 		PanicSanity("Remove(e) with false tail")
 	}

 	// If we're removing the only item, make CList FrontWait/BackWait wait.
 	if l.len == 1 {
 		l.wg.Add(1)
 	}
 	l.len -= 1

 	// Modify e.prev and e.next and connect
 	if prev != nil {
 		prev.setNextAtomic(next)
 	}
 	if next != nil {
 		next.setPrevAtomic(prev)
 	}

 	// Mark e as removed so NextWait/PrevWait can return.
 	e.setRemovedAtomic()

 	// Set .Done() on e, otherwise waiters will wait forever.
 	if prev == nil {
 		e.prevWg.Done()
 	}
 	if next == nil {
 		e.nextWg.Done()
 	}

 	return e.Value
 }

 func waitGroup1() (wg *sync.WaitGroup) {
 	wg = &sync.WaitGroup{}
 	wg.Add(1)
 	return
 }