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versioned_signal.go
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versioned_signal.go
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package synckit
import (
"sync"
"sync/atomic"
"unsafe"
)
func NewVersionedSignal() VersionedSignal {
return VersionedSignal{}
}
type VersionedSignal struct {
signalVersion *SignalVersion // atomic
}
func (p *VersionedSignal) _signalVersion() *unsafe.Pointer {
return (*unsafe.Pointer)((unsafe.Pointer)(&p.signalVersion))
}
func (p *VersionedSignal) NextBroadcast() {
sv := (*SignalVersion)(atomic.SwapPointer(p._signalVersion(), nil))
sv.signal()
}
func (p *VersionedSignal) BroadcastAndMark() *SignalVersion {
nsv := newSignalVersion()
sv := (*SignalVersion)(atomic.SwapPointer(p._signalVersion(), (unsafe.Pointer)(nsv)))
sv.signal()
return nsv
}
func (p *VersionedSignal) Mark() *SignalVersion {
var nsv *SignalVersion
for {
sv := (*SignalVersion)(atomic.LoadPointer(p._signalVersion()))
switch {
case sv != nil:
return sv
case nsv == nil: // avoid repetitive new
nsv = newSignalVersion()
}
if atomic.CompareAndSwapPointer(p._signalVersion(), nil, (unsafe.Pointer)(nsv)) {
return nsv
}
}
}
func NewNeverSignal() *SignalVersion {
return newSignalVersion()
}
func newSignalVersion() *SignalVersion {
sv := SignalVersion{}
sv.wg.Add(1)
return &sv
}
type signalChannel = chan struct{}
type SignalVersion struct {
next *SignalVersion
wg sync.WaitGroup // is cheaper than channel and doesn't need additional heap allocation
c *signalChannel // atomic
}
func (p *SignalVersion) _signalChannel() *unsafe.Pointer {
return (*unsafe.Pointer)((unsafe.Pointer)(&p.c))
}
func (p *SignalVersion) getSignalChannel() *signalChannel {
return (*signalChannel)(atomic.LoadPointer(p._signalChannel()))
}
func (p *SignalVersion) signal() {
if p == nil {
return
}
p.next.signal() // older signals must fire first
var closedSignal *SignalChannel // explicit type decl to avoid passing of something wrong into unsafe.Pointer conversion
closedSignal = &closedChan
atomic.CompareAndSwapPointer(p._signalChannel(), nil, (unsafe.Pointer)(closedSignal))
p.wg.Done()
}
func (p *SignalVersion) Wait() {
if p == nil {
return
}
p.wg.Wait()
}
func (p *SignalVersion) ChannelIf(choice bool, def <-chan struct{}) <-chan struct{} {
if choice {
return p.Channel()
}
return def
}
func (p *SignalVersion) Channel() <-chan struct{} {
if p == nil {
return ClosedChannel()
}
var wcp *signalChannel
for {
switch sc := p.getSignalChannel(); {
case sc != nil:
return *sc
case wcp == nil:
wcp = new(signalChannel)
*wcp = make(signalChannel)
}
if atomic.CompareAndSwapPointer(p._signalChannel(), nil, (unsafe.Pointer)(wcp)) {
go p.waitClose(wcp)
return *wcp
}
}
}
func (p *SignalVersion) waitClose(wcp *signalChannel) {
p.wg.Wait()
close(*wcp)
}
func (p *SignalVersion) HasSignal() bool {
if p == nil {
return true
}
sc := p.getSignalChannel()
if sc == nil {
return false
}
select {
case <-*sc:
return true
default:
return false
}
}