// WithProcessClosing returns a context.Context derived from ctx that
// is cancelled as p is Closing (after: <-p.Closing()). It is simply:
//
// func WithProcessClosing(ctx context.Context, p goprocess.Process) context.Context {
// ctx, cancel := context.WithCancel(ctx)
// go func() {
// <-p.Closing()
// cancel()
// }()
// return ctx
// }
//
func WithProcessClosing(ctx context.Context, p goprocess.Process) context.Context {
ctx, cancel := context.WithCancel(ctx)
go func() {
<-p.Closing()
cancel()
}()
return ctx
}
func (d *datastore) runQuery(worker goprocess.Process, qrb *dsq.ResultBuilder) {
var rnge *util.Range
if qrb.Query.Prefix != "" {
rnge = util.BytesPrefix([]byte(qrb.Query.Prefix))
}
i := d.DB.NewIterator(rnge, nil)
defer i.Release()
// advance iterator for offset
if qrb.Query.Offset > 0 {
for j := 0; j < qrb.Query.Offset; j++ {
i.Next()
}
}
// iterate, and handle limit, too
for sent := 0; i.Next(); sent++ {
// end early if we hit the limit
if qrb.Query.Limit > 0 && sent >= qrb.Query.Limit {
break
}
k := ds.NewKey(string(i.Key())).String()
e := dsq.Entry{Key: k}
if !qrb.Query.KeysOnly {
buf := make([]byte, len(i.Value()))
copy(buf, i.Value())
e.Value = buf
}
select {
case qrb.Output <- dsq.Result{Entry: e}: // we sent it out
case <-worker.Closing(): // client told us to end early.
break
}
}
if err := i.Error(); err != nil {
select {
case qrb.Output <- dsq.Result{Error: err}: // client read our error
case <-worker.Closing(): // client told us to end.
return
}
}
}
// transport will grab message arrival times, wait until that time, and
// then write the message out when it is scheduled to arrive
func (s *stream) transport(proc process.Process) {
bufsize := 256
buf := new(bytes.Buffer)
ticker := time.NewTicker(time.Millisecond * 4)
// writeBuf writes the contents of buf through to the s.Writer.
// done only when arrival time makes sense.
drainBuf := func() {
if buf.Len() > 0 {
_, err := s.Pipe.Write(buf.Bytes())
if err != nil {
return
}
buf.Reset()
}
}
// deliverOrWait is a helper func that processes
// an incoming packet. it waits until the arrival time,
// and then writes things out.
deliverOrWait := func(o *transportObject) {
buffered := len(o.msg) + buf.Len()
now := time.Now()
if now.Before(o.arrivalTime) {
if buffered < bufsize {
buf.Write(o.msg)
return
}
// we do not buffer + return here, instead hanging the
// call (i.e. not accepting any more transportObjects)
// so that we apply back-pressure to the sender.
// this sleep should wake up same time as ticker.
time.Sleep(o.arrivalTime.Sub(now))
}
// ok, we waited our due time. now rite the buf + msg.
// drainBuf first, before we write this message.
drainBuf()
// write this message.
_, err := s.Pipe.Write(o.msg)
if err != nil {
log.Error("mock_stream", err)
}
}
for {
select {
case <-proc.Closing():
return // bail out of here.
case o, ok := <-s.toDeliver:
if !ok {
return
}
deliverOrWait(o)
case <-ticker.C: // ok, due to write it out.
drainBuf()
}
}
}