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|
package dbus
import (
"sync"
)
// NewSequentialSignalHandler returns an instance of a new
// signal handler that guarantees sequential processing of signals. It is a
// guarantee of this signal handler that signals will be written to
// channels in the order they are received on the DBus connection.
func NewSequentialSignalHandler() SignalHandler {
return &sequentialSignalHandler{}
}
type sequentialSignalHandler struct {
mu sync.RWMutex
closed bool
signals []*sequentialSignalChannelData
}
func (sh *sequentialSignalHandler) DeliverSignal(intf, name string, signal *Signal) {
sh.mu.RLock()
defer sh.mu.RUnlock()
if sh.closed {
return
}
for _, scd := range sh.signals {
scd.deliver(signal)
}
}
func (sh *sequentialSignalHandler) Terminate() {
sh.mu.Lock()
defer sh.mu.Unlock()
if sh.closed {
return
}
for _, scd := range sh.signals {
scd.close()
close(scd.ch)
}
sh.closed = true
sh.signals = nil
}
func (sh *sequentialSignalHandler) AddSignal(ch chan<- *Signal) {
sh.mu.Lock()
defer sh.mu.Unlock()
if sh.closed {
return
}
sh.signals = append(sh.signals, newSequentialSignalChannelData(ch))
}
func (sh *sequentialSignalHandler) RemoveSignal(ch chan<- *Signal) {
sh.mu.Lock()
defer sh.mu.Unlock()
if sh.closed {
return
}
for i := len(sh.signals) - 1; i >= 0; i-- {
if ch == sh.signals[i].ch {
sh.signals[i].close()
copy(sh.signals[i:], sh.signals[i+1:])
sh.signals[len(sh.signals)-1] = nil
sh.signals = sh.signals[:len(sh.signals)-1]
}
}
}
type sequentialSignalChannelData struct {
ch chan<- *Signal
in chan *Signal
done chan struct{}
}
func newSequentialSignalChannelData(ch chan<- *Signal) *sequentialSignalChannelData {
scd := &sequentialSignalChannelData{
ch: ch,
in: make(chan *Signal),
done: make(chan struct{}),
}
go scd.bufferSignals()
return scd
}
func (scd *sequentialSignalChannelData) bufferSignals() {
defer close(scd.done)
// Ensure that signals are delivered to scd.ch in the same
// order they are received from scd.in.
var queue []*Signal
for {
if len(queue) == 0 {
signal, ok := <- scd.in
if !ok {
return
}
queue = append(queue, signal)
}
select {
case scd.ch <- queue[0]:
copy(queue, queue[1:])
queue[len(queue)-1] = nil
queue = queue[:len(queue)-1]
case signal, ok := <-scd.in:
if !ok {
return
}
queue = append(queue, signal)
}
}
}
func (scd *sequentialSignalChannelData) deliver(signal *Signal) {
scd.in <- signal
}
func (scd *sequentialSignalChannelData) close() {
close(scd.in)
// Ensure that bufferSignals() has exited and won't attempt
// any future sends on scd.ch
<-scd.done
}
|
