From 616f39592086ac3c56591c22be91459d1ec324c6 Mon Sep 17 00:00:00 2001
From: Anthony Romano <anthony.romano@coreos.com>
Date: Thu, 11 Feb 2016 19:21:30 -0800
Subject: [PATCH] etcdserver: use fifo scheduler for applier

---
 etcdserver/server.go | 64 +++++++++++---------------------------------
 1 file changed, 16 insertions(+), 48 deletions(-)

diff --git a/etcdserver/server.go b/etcdserver/server.go
index c1208c605..8be2eb45a 100644
--- a/etcdserver/server.go
+++ b/etcdserver/server.go
@@ -39,6 +39,7 @@ import (
 	"github.com/coreos/etcd/pkg/idutil"
 	"github.com/coreos/etcd/pkg/pbutil"
 	"github.com/coreos/etcd/pkg/runtime"
+	"github.com/coreos/etcd/pkg/schedule"
 	"github.com/coreos/etcd/pkg/timeutil"
 	"github.com/coreos/etcd/pkg/types"
 	"github.com/coreos/etcd/pkg/wait"
@@ -487,51 +488,6 @@ type etcdProgress struct {
 	appliedi  uint64
 }
 
-// startApplier buffers apply operations so raftNode won't block on sending
-// new applies, timing out (since applies can be slow). The goroutine begins
-// shutdown on close(s.done) and closes the returned channel when finished.
-func (s *EtcdServer) startApplier(ep etcdProgress) <-chan struct{} {
-	donec := make(chan struct{})
-	go func() {
-		defer close(donec)
-		pending := []apply{}
-		sdonec := s.done
-		apdonec := make(chan struct{})
-		// serialized function
-		f := func(ap apply) {
-			s.applyAll(&ep, &ap)
-			select {
-			// snapshot requested via send()
-			case m := <-s.msgSnapC:
-				merged := s.createMergedSnapshotMessage(m, ep.appliedi, ep.confState)
-				s.sendMergedSnap(merged)
-			default:
-			}
-			apdonec <- struct{}{}
-		}
-		for sdonec != nil || len(pending) > 0 {
-			select {
-			// launch if no pending apply packet, queue up the rest
-			case ap := <-s.r.apply():
-				pending = append(pending, ap)
-				if len(pending) == 1 {
-					go f(pending[0])
-				}
-			// pending apply serviced, schedule the next one
-			case <-apdonec:
-				pending = pending[1:]
-				if len(pending) != 0 {
-					go f(pending[0])
-				}
-			// run() is finished; drain pending and exit
-			case <-sdonec:
-				sdonec = nil
-			}
-		}
-	}()
-	return donec
-}
-
 func (s *EtcdServer) run() {
 	snap, err := s.r.raftStorage.Snapshot()
 	if err != nil {
@@ -540,14 +496,17 @@ func (s *EtcdServer) run() {
 	s.r.start(s)
 
 	// asynchronously accept apply packets, dispatch progress in-order
-	appdonec := s.startApplier(etcdProgress{
+	sched := schedule.NewFIFOScheduler()
+	ep := etcdProgress{
 		confState: snap.Metadata.ConfState,
 		snapi:     snap.Metadata.Index,
 		appliedi:  snap.Metadata.Index,
-	})
+	}
 
 	defer func() {
 		s.r.stop()
+		sched.Stop()
+
 		// kv, lessor and backend can be nil if running without v3 enabled
 		// or running unit tests.
 		if s.lessor != nil {
@@ -560,7 +519,6 @@ func (s *EtcdServer) run() {
 			s.be.Close()
 		}
 		close(s.done)
-		<-appdonec
 	}()
 
 	var expiredLeaseC <-chan []*lease.Lease
@@ -570,6 +528,9 @@ func (s *EtcdServer) run() {
 
 	for {
 		select {
+		case ap := <-s.r.apply():
+			f := func(context.Context) { s.applyAll(&ep, &ap) }
+			sched.Schedule(f)
 		case leases := <-expiredLeaseC:
 			go func() {
 				for _, l := range leases {
@@ -594,6 +555,13 @@ func (s *EtcdServer) applyAll(ep *etcdProgress, apply *apply) {
 	// storage, since the raft routine might be slower than apply routine.
 	<-apply.raftDone
 	s.triggerSnapshot(ep)
+	select {
+	// snapshot requested via send()
+	case m := <-s.msgSnapC:
+		merged := s.createMergedSnapshotMessage(m, ep.appliedi, ep.confState)
+		s.sendMergedSnap(merged)
+	default:
+	}
 }
 
 func (s *EtcdServer) applySnapshot(ep *etcdProgress, apply *apply) {