Split out notifying /sync requests and calculating sync responses (#96)

* Split out notifying /sync requests and calculating sync responses

The logic for notifying /sync requests is about to get really
complicated as we optimise when to wake up requests, so split
out that code into a separate struct to isolate it and make
it easier to unit test.

src/github.com/matrix-org/dendrite/cmd/dendrite-sync-api-server/main.go

@@ -26,6 +26,7 @@ import (
 	"github.com/matrix-org/dendrite/syncapi/routing"
 	"github.com/matrix-org/dendrite/syncapi/storage"
 	"github.com/matrix-org/dendrite/syncapi/sync"
+	"github.com/matrix-org/dendrite/syncapi/types"
 
 	log "github.com/Sirupsen/logrus"
 	yaml "gopkg.in/yaml.v2"
@@ -71,12 +72,13 @@ func main() {
 		log.Panicf("startup: failed to create sync server database with data source %s : %s", cfg.DataSource, err)
 	}
 
-	rp, err := sync.NewRequestPool(db)
+	pos, err := db.SyncStreamPosition()
 	if err != nil {
-		log.Panicf("startup: Failed to create request pool : %s", err)
+		log.Panicf("startup: failed to get latest sync stream position : %s", err)
 	}
 
-	server, err := consumers.NewServer(cfg, rp, db)
+	n := sync.NewNotifier(types.StreamPosition(pos))
+	server, err := consumers.NewServer(cfg, n, db)
 	if err != nil {
 		log.Panicf("startup: failed to create sync server: %s", err)
 	}
@@ -85,6 +87,6 @@ func main() {
 	}
 
 	log.Info("Starting sync server on ", *bindAddr)
-	routing.SetupSyncServerListeners(http.DefaultServeMux, http.DefaultClient, *cfg, rp)
+	routing.SetupSyncServerListeners(http.DefaultServeMux, http.DefaultClient, *cfg, sync.NewRequestPool(db, n))
 	log.Fatal(http.ListenAndServe(*bindAddr, nil))
 }

src/github.com/matrix-org/dendrite/syncapi/consumers/roomserver.go

@@ -32,11 +32,11 @@ import (
 type Server struct {
 	roomServerConsumer *common.ContinualConsumer
 	db                 *storage.SyncServerDatabase
-	rp                 *sync.RequestPool
+	notifier           *sync.Notifier
 }
 
 // NewServer creates a new sync server. Call Start() to begin consuming from room servers.
-func NewServer(cfg *config.Sync, rp *sync.RequestPool, store *storage.SyncServerDatabase) (*Server, error) {
+func NewServer(cfg *config.Sync, n *sync.Notifier, store *storage.SyncServerDatabase) (*Server, error) {
 	kafkaConsumer, err := sarama.NewConsumer(cfg.KafkaConsumerURIs, nil)
 	if err != nil {
 		return nil, err
@@ -50,7 +50,7 @@ func NewServer(cfg *config.Sync, rp *sync.RequestPool, store *storage.SyncServer
 	s := &Server{
 		roomServerConsumer: &consumer,
 		db:                 store,
-		rp:                 rp,
+		notifier:           n,
 	}
 	consumer.ProcessMessage = s.onMessage
 
@@ -96,7 +96,7 @@ func (s *Server) onMessage(msg *sarama.ConsumerMessage) error {
 		}).Panicf("roomserver output log: write event failure")
 		return nil
 	}
-	s.rp.OnNewEvent(&ev, types.StreamPosition(syncStreamPos))
+	s.notifier.OnNewEvent(&ev, types.StreamPosition(syncStreamPos))
 
 	return nil
 }

src/github.com/matrix-org/dendrite/syncapi/sync/notifier.go

@@ -0,0 +1,67 @@
+// Copyright 2017 Vector Creations Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sync
+
+import (
+	"sync"
+
+	"github.com/matrix-org/dendrite/syncapi/types"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+// Notifier will wake up sleeping requests in the request pool when there
+// is some new data. It does not tell requests what that data is, only the
+// stream position which they can use to get at it.
+type Notifier struct {
+	// The latest sync stream position: guarded by 'cond'.
+	currPos types.StreamPosition
+	// A condition variable to notify all waiting goroutines of a new sync stream position
+	cond *sync.Cond
+}
+
+// NewNotifier creates a new notifier set to the given stream position.
+func NewNotifier(pos types.StreamPosition) *Notifier {
+	return &Notifier{
+		pos,
+		sync.NewCond(&sync.Mutex{}),
+	}
+}
+
+// OnNewEvent is called when a new event is received from the room server. Must only be
+// called from a single goroutine, to avoid races between updates which could set the
+// current position in the stream incorrectly.
+func (n *Notifier) OnNewEvent(ev *gomatrixserverlib.Event, pos types.StreamPosition) {
+	// update the current position in a guard and then notify all /sync streams
+	n.cond.L.Lock()
+	n.currPos = pos
+	n.cond.L.Unlock()
+
+	n.cond.Broadcast() // notify ALL waiting goroutines
+}
+
+// WaitForEvents blocks until there are new events for this request.
+func (n *Notifier) WaitForEvents(req syncRequest) types.StreamPosition {
+	// In a guard, check if the /sync request should block, and block it until we get a new position
+	n.cond.L.Lock()
+	currentPos := n.currPos
+	for req.since == currentPos {
+		// we need to wait for a new event.
+		// TODO: This waits for ANY new event, we need to only wait for events which we care about.
+		n.cond.Wait() // atomically unlocks and blocks goroutine, then re-acquires lock on unblock
+		currentPos = n.currPos
+	}
+	n.cond.L.Unlock()
+	return currentPos
+}

src/github.com/matrix-org/dendrite/syncapi/sync/requestpool.go

@@ -16,7 +16,6 @@ package sync
 
 import (
 	"net/http"
-	"sync"
 	"time"
 
 	log "github.com/Sirupsen/logrus"
@@ -32,19 +31,12 @@ import (
 // RequestPool manages HTTP long-poll connections for /sync
 type RequestPool struct {
 	db       *storage.SyncServerDatabase
-	// The latest sync stream position: guarded by 'cond'.
-	currPos types.StreamPosition
-	// A condition variable to notify all waiting goroutines of a new sync stream position
-	cond *sync.Cond
+	notifier *Notifier
 }
 
 // NewRequestPool makes a new RequestPool
-func NewRequestPool(db *storage.SyncServerDatabase) (*RequestPool, error) {
-	pos, err := db.SyncStreamPosition()
-	if err != nil {
-		return nil, err
-	}
-	return &RequestPool{db, types.StreamPosition(pos), sync.NewCond(&sync.Mutex{})}, nil
+func NewRequestPool(db *storage.SyncServerDatabase, n *Notifier) *RequestPool {
+	return &RequestPool{db, n}
 }
 
 // OnIncomingSyncRequest is called when a client makes a /sync request. This function MUST be
@@ -106,34 +98,8 @@ func (rp *RequestPool) OnIncomingSyncRequest(req *http.Request) util.JSONRespons
 	}
 }
 
-// OnNewEvent is called when a new event is received from the room server. Must only be
-// called from a single goroutine, to avoid races between updates which could set the
-// current position in the stream incorrectly.
-func (rp *RequestPool) OnNewEvent(ev *gomatrixserverlib.Event, pos types.StreamPosition) {
-	// update the current position in a guard and then notify all /sync streams
-	rp.cond.L.Lock()
-	rp.currPos = pos
-	rp.cond.L.Unlock()
-
-	rp.cond.Broadcast() // notify ALL waiting goroutines
-}
-
-func (rp *RequestPool) waitForEvents(req syncRequest) types.StreamPosition {
-	// In a guard, check if the /sync request should block, and block it until we get a new position
-	rp.cond.L.Lock()
-	currentPos := rp.currPos
-	for req.since == currentPos {
-		// we need to wait for a new event.
-		// TODO: This waits for ANY new event, we need to only wait for events which we care about.
-		rp.cond.Wait() // atomically unlocks and blocks goroutine, then re-acquires lock on unblock
-		currentPos = rp.currPos
-	}
-	rp.cond.L.Unlock()
-	return currentPos
-}
-
 func (rp *RequestPool) currentSyncForUser(req syncRequest) (*types.Response, error) {
-	currentPos := rp.waitForEvents(req)
+	currentPos := rp.notifier.WaitForEvents(req)
 
 	if req.since == types.StreamPosition(0) {
 		pos, data, err := rp.db.CompleteSync(req.userID, req.limit)