fix rampant memory leak in providers records storage

address comments from CR

use map and array combo for better perf

providers.go

@@ -10,15 +10,13 @@ import (
 	context "github.com/ipfs/go-ipfs/Godeps/_workspace/src/golang.org/x/net/context"
 )
 
-type providerInfo struct {
-	Creation time.Time
-	Value    peer.ID
-}
-
 type ProviderManager struct {
-	providers map[key.Key][]*providerInfo
+	// all non channel fields are meant to be accessed only within
+	// the run method
+	providers map[key.Key]*providerSet
 	local     map[key.Key]struct{}
 	lpeer     peer.ID
+
 	getlocal chan chan []key.Key
 	newprovs chan *addProv
 	getprovs chan *getProv
@@ -26,6 +24,11 @@ type ProviderManager struct {
 	ctxgroup.ContextGroup
 }
 
+type providerSet struct {
+	providers []peer.ID
+	set       map[peer.ID]time.Time
+}
+
 type addProv struct {
 	k   key.Key
 	val peer.ID
@@ -40,7 +43,7 @@ func NewProviderManager(ctx context.Context, local peer.ID) *ProviderManager {
 	pm := new(ProviderManager)
 	pm.getprovs = make(chan *getProv)
 	pm.newprovs = make(chan *addProv)
-	pm.providers = make(map[key.Key][]*providerInfo)
+	pm.providers = make(map[key.Key]*providerSet)
 	pm.getlocal = make(chan chan []key.Key)
 	pm.local = make(map[key.Key]struct{})
 	pm.ContextGroup = ctxgroup.WithContext(ctx)
@@ -61,18 +64,20 @@ func (pm *ProviderManager) run() {
 			if np.val == pm.lpeer {
 				pm.local[np.k] = struct{}{}
 			}
-			pi := new(providerInfo)
-			pi.Creation = time.Now()
-			pi.Value = np.val
-			arr := pm.providers[np.k]
-			pm.providers[np.k] = append(arr, pi)
+			provs, ok := pm.providers[np.k]
+			if !ok {
+				provs = newProviderSet()
+				pm.providers[np.k] = provs
+			}
+			provs.Add(np.val)
 
 		case gp := <-pm.getprovs:
 			var parr []peer.ID
-			provs := pm.providers[gp.k]
-			for _, p := range provs {
-				parr = append(parr, p.Value)
+			provs, ok := pm.providers[gp.k]
+			if ok {
+				parr = provs.providers
 			}
+
 			gp.resp <- parr
 
 		case lc := <-pm.getlocal:
@@ -83,14 +88,16 @@ func (pm *ProviderManager) run() {
 			lc <- keys
 
 		case <-tick.C:
-			for k, provs := range pm.providers {
-				var filtered []*providerInfo
-				for _, p := range provs {
-					if time.Now().Sub(p.Creation) < time.Hour*24 {
+			for _, provs := range pm.providers {
+				var filtered []peer.ID
+				for p, t := range provs.set {
+					if time.Now().Sub(t) > time.Hour*24 {
+						delete(provs.set, p)
+					} else {
 						filtered = append(filtered, p)
 					}
 				}
-				pm.providers[k] = filtered
+				provs.providers = filtered
 			}
 
 		case <-pm.Closing():
@@ -133,3 +140,18 @@ func (pm *ProviderManager) GetLocal() []key.Key {
 	pm.getlocal <- resp
 	return <-resp
 }
+
+func newProviderSet() *providerSet {
+	return &providerSet{
+		set: make(map[peer.ID]time.Time),
+	}
+}
+
+func (ps *providerSet) Add(p peer.ID) {
+	_, found := ps.set[p]
+	if !found {
+		ps.providers = append(ps.providers, p)
+	}
+
+	ps.set[p] = time.Now()
+}