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tun: windows: spin for a bit before falling back to event object

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This commit is contained in:
Jason A. Donenfeld 2019-07-17 09:06:34 +02:00
parent 2e24e7dcae
commit 9ea9a92117
1 changed files with 19 additions and 4 deletions
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23
tun/tun_windows.go
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@ -267,6 +267,9 @@ func (tun *NativeTun) ForceMTU(mtu int) {
tun.forcedMTU = mtu
}
//go:linkname procyield runtime.procyield
func procyield(cycles uint32)
// Note: Read() and Write() assume the caller comes only from a single thread; there's no locking.
func (tun *NativeTun) Read(buff []byte, offset int) (int, error) {
@ -277,6 +280,7 @@ func (tun *NativeTun) Read(buff []byte, offset int) (int, error) {
}
retries := maybeRetry(1000)
top:
for !tun.close {
_, err := tun.getTUN()
if err != nil {
@ -288,10 +292,21 @@ func (tun *NativeTun) Read(buff []byte, offset int) (int, error) {
return 0, errors.New("send ring head out of bounds")
}
buffTail := atomic.LoadUint32(&tun.rings.send.ring.tail)
if buffHead == buffTail {
windows.WaitForSingleObject(tun.rings.send.tailMoved, windows.INFINITE)
continue
start := time.Now()
var buffTail uint32
for {
buffTail = atomic.LoadUint32(&tun.rings.send.ring.tail)
if buffHead != buffTail {
break
}
if tun.close {
return 0, os.ErrClosed
}
if time.Since(start) >= time.Millisecond*50 {
windows.WaitForSingleObject(tun.rings.send.tailMoved, windows.INFINITE)
continue top
}
procyield(1)
}
if buffTail >= packetCapacity {
if retries > 0 {