From 99b2923ce754580fdf436ce631eaa218142f1e84 Mon Sep 17 00:00:00 2001
From: Kegan Dougal <kegan@matrix.org>
Date: Fri, 7 Apr 2017 14:33:28 +0100
Subject: [PATCH] WIP waiting on Cond

---
 .../dendrite/clientapi/sync/requestpool.go    | 46 +++++++++++++------
 1 file changed, 33 insertions(+), 13 deletions(-)

diff --git a/src/github.com/matrix-org/dendrite/clientapi/sync/requestpool.go b/src/github.com/matrix-org/dendrite/clientapi/sync/requestpool.go
index 2465be0c5..c97d011a5 100644
--- a/src/github.com/matrix-org/dendrite/clientapi/sync/requestpool.go
+++ b/src/github.com/matrix-org/dendrite/clientapi/sync/requestpool.go
@@ -1,9 +1,11 @@
 package sync
 
 import (
+	"context"
 	"fmt"
 	"net/http"
 	"strconv"
+	"sync"
 	"time"
 
 	log "github.com/Sirupsen/logrus"
@@ -26,8 +28,11 @@ type syncRequest struct {
 
 // RequestPool manages HTTP long-poll connections for /sync
 type RequestPool struct {
-	db      *storage.SyncServerDatabase
+	db *storage.SyncServerDatabase
+	// The latest sync stream position: guarded by 'cond'.
 	currPos syncStreamPosition
+	// A condition variable to notify all waiting goroutines of a new sync stream position
+	cond *sync.Cond
 }
 
 // OnIncomingSyncRequest is called when a client makes a /sync request. This function MUST be
@@ -61,9 +66,14 @@ func (rp *RequestPool) OnIncomingSyncRequest(req *http.Request) util.JSONRespons
 		"userID":  userID,
 		"since":   since,
 		"timeout": timeout,
+		"current": rp.currPos,
 	}).Info("Incoming /sync request")
 
-	res, err := rp.currentSyncForUser(syncReq)
+	// set the timeout going
+	ctx, cancel := context.WithTimeout(req.Context(), timeout)
+	defer cancel()
+
+	res, err := rp.currentSyncForUser(ctx, syncReq)
 	if err != nil {
 		return httputil.LogThenError(req, err)
 	}
@@ -76,16 +86,32 @@ 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.
 func (rp *RequestPool) OnNewEvent(ev *gomatrixserverlib.Event, pos syncStreamPosition) {
+	// update the current position in a guard and then notify all /sync streams
+	rp.cond.L.Lock()
 	fmt.Println("OnNewEvent =>", ev.EventID(), " pos=", pos, " old_pos=", rp.currPos)
 	rp.currPos = pos
+	rp.cond.L.Unlock()
+
+	rp.cond.Broadcast() // notify ALL waiting goroutines
 }
 
-func (rp *RequestPool) currentSyncForUser(req syncRequest) ([]gomatrixserverlib.Event, error) {
-	if req.since == rp.currPos {
-		// wait for new event
+func (rp *RequestPool) waitForEvents(req syncRequest) syncStreamPosition {
+	// 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
+}
 
-	return rp.db.EventsInRange(int64(req.since), int64(rp.currPos))
+func (rp *RequestPool) currentSyncForUser(ctx context.Context, req syncRequest) ([]gomatrixserverlib.Event, error) {
+	currentPos := rp.waitForEvents(req)
+	return rp.db.EventsInRange(int64(req.since), int64(currentPos))
 
 	// https://github.com/matrix-org/synapse/blob/v0.19.3/synapse/handlers/sync.py#L179
 	// Check if we are going to return immediately and if so, calculate the current
@@ -112,12 +138,6 @@ func (rp *RequestPool) currentSyncForUser(req syncRequest) ([]gomatrixserverlib.
 
 	// Steps: (partial token, more than threshold (too expensive to do the above))
 	// - Ignore for now, meaning this code path will be horrendously slow.
-
-	// TODO: wait for an event which affects this user or one of their rooms, then recheck for new
-	// sync data.
-	time.Sleep(req.timeout)
-
-	return nil, nil
 }
 
 func getTimeout(timeoutMS string) time.Duration {
@@ -148,5 +168,5 @@ func NewRequestPool(db *storage.SyncServerDatabase) (*RequestPool, error) {
 	if err != nil {
 		return nil, err
 	}
-	return &RequestPool{db, syncStreamPosition(pos)}, nil
+	return &RequestPool{db, syncStreamPosition(pos), sync.NewCond(&sync.Mutex{})}, nil
 }