From 9c68c949e2992df06879990eb39327acafe1b4d2 Mon Sep 17 00:00:00 2001
From: Katie Knister <kateknister@google.com>
Date: Wed, 18 Feb 2015 16:14:16 -0800
Subject: [PATCH] added locks to make events library threadsafe

---
 events/handler.go | 40 +++++++++++++++++++++++++++++++++-------
 1 file changed, 33 insertions(+), 7 deletions(-)

diff --git a/events/handler.go b/events/handler.go
index 4a59ff0d..d7a57bbd 100644
--- a/events/handler.go
+++ b/events/handler.go
@@ -18,6 +18,7 @@ import (
 	"errors"
 	"sort"
 	"strings"
+	"sync"
 	"time"
 )
 
@@ -47,6 +48,10 @@ type events struct {
 	// satisfy the request of a given watch object in watchers, the event
 	// is sent over the channel to that caller of WatchEvents
 	watchers []*watch
+	// lock that blocks eventlist from being accessed until a writer releases it
+	eventsLock sync.RWMutex
+	// lock that blocks watchers from being accessed until a writer releases it
+	watcherLock sync.RWMutex
 }
 
 // initialized by a call to WatchEvents(), a watch struct will then be added
@@ -213,6 +218,8 @@ func checkIfEventSatisfiesRequest(request *Request, event *Event) bool {
 // up to the most recent MaxEventsReturned events in that time range are returned.
 func (self *events) GetEvents(request *Request) (EventSlice, error) {
 	returnEventList := EventSlice{}
+	self.eventsLock.RLock()
+	defer self.eventsLock.RUnlock()
 	for _, e := range self.eventlist {
 		if checkIfEventSatisfiesRequest(request, e) {
 			returnEventList = append(returnEventList, e)
@@ -233,21 +240,40 @@ func (self *events) WatchEvents(outChannel chan *Event, request *Request) error
 			"for a call to watch, request.StartTime and request.EndTime must be uninitialized")
 	}
 	newWatcher := newWatch(request, outChannel)
+	self.watcherLock.Lock()
+	defer self.watcherLock.Unlock()
 	self.watchers = append(self.watchers, newWatcher)
 	return nil
 }
 
+// helper function to update the event manager's eventlist
+func (self *events) updateEventList(e *Event) {
+	self.eventsLock.Lock()
+	defer self.eventsLock.Unlock()
+	self.eventlist = append(self.eventlist, e)
+}
+
+func (self *events) findValidWatchers(e *Event) []*watch {
+	watchesToSend := make([]*watch, 0)
+	self.watcherLock.RLock()
+	defer self.watcherLock.RUnlock()
+	for _, watcher := range self.watchers {
+		watchRequest := watcher.request
+		if checkIfEventSatisfiesRequest(watchRequest, e) {
+			watchesToSend = append(watchesToSend, watcher)
+		}
+	}
+	return watchesToSend
+}
+
 // method of Events object that adds the argument Event object to the
 // eventlist. It also feeds the event to a set of watch channels
 // held by the manager if it satisfies the request keys of the channels
 func (self *events) AddEvent(e *Event) error {
-	self.eventlist = append(self.eventlist, e)
-	for _, watcher := range self.watchers {
-		watchRequest := watcher.request
-		inChannel := watcher.channel
-		if checkIfEventSatisfiesRequest(watchRequest, e) {
-			inChannel <- e
-		}
+	self.updateEventList(e)
+	watchesToSend := self.findValidWatchers(e)
+	for _, watchObject := range watchesToSend {
+		watchObject.channel <- e
 	}
 	return nil
 }