Add path map and convert asink client event processing to that model

client/path_map.go

@@ -0,0 +1,93 @@
+package main
+
+import (
+	"asink"
+)
+
+type pathMapRequest struct {
+	path         string
+	local        bool /*is this event local (true) or remote(false)?*/
+	responseChan chan *asink.Event
+}
+
+type pathMapValue struct {
+	latestEvent   *asink.Event
+	locked        bool
+	localWaiters  []chan *asink.Event
+	remoteWaiters []chan *asink.Event
+}
+
+var pathLockerChan = make(chan *pathMapRequest)
+var pathUnlockerChan = make(chan *asink.Event)
+
+func PathLocker(db *AsinkDB) {
+	var event *asink.Event
+	var request *pathMapRequest
+	var v *pathMapValue
+	var ok bool
+	var c chan *asink.Event
+	m := make(map[string]*pathMapValue)
+
+	for {
+		select {
+		case event = <-pathUnlockerChan:
+			if v, ok = m[event.Path]; ok != false {
+				if v.latestEvent == nil || !v.latestEvent.IsSameEvent(event) {
+					err := db.DatabaseAddEvent(event)
+					if err != nil {
+						panic(err)
+					}
+					//TODO batch database writes instead of doing one at a time
+				}
+				v.latestEvent = event
+				if len(v.localWaiters) > 0 {
+					c = v.localWaiters[0]
+					v.localWaiters = v.localWaiters[1:]
+					c <- event
+				} else if len(v.remoteWaiters) > 0 {
+					c = v.remoteWaiters[0]
+					v.remoteWaiters = v.remoteWaiters[1:]
+					c <- event
+				} else {
+					v.locked = false
+				}
+			}
+		case request = <-pathLockerChan:
+			v, ok = m[request.path]
+			//allocate pathMapValue object if it doesn't exist
+			if !ok {
+				v = new(pathMapValue)
+				m[request.path] = v
+			}
+			if v.locked {
+				if request.local {
+					v.localWaiters = append(v.localWaiters, request.responseChan)
+				} else {
+					v.remoteWaiters = append(v.remoteWaiters, request.responseChan)
+				}
+			} else {
+				v.locked = true
+				event, err := db.DatabaseLatestEventForPath(request.path)
+				if err != nil {
+					panic(err)
+				}
+				request.responseChan <- event
+			}
+		}
+	}
+}
+
+//locks the path to ensure nothing else inside asink is mucking with that file.
+//'local' determines the precedence of the lock - all local lock requesters will
+//be served before any remote requesters.
+//The previous event for this path is returned, nil is returned if no previous event exists
+func LockPath(path string, local bool) (currentEvent *asink.Event) {
+	c := make(chan *asink.Event)
+	pathLockerChan <- &pathMapRequest{path, local, c}
+	return <-c
+}
+
+//unlocks the path, storing the updated event back to the database
+func UnlockPath(event *asink.Event) {
+	pathUnlockerChan <- event
+}