Fix cache pointer race condition with atomic.Pointer

Use atomic.Pointer for vidMap cache field to prevent data races
during cache trimming in resetVidMap. This addresses the race condition
where concurrent GetLocations calls could read the cache pointer while
resetVidMap is modifying it during cache chain trimming.

Changes:
- Changed cache field from *vidMap to atomic.Pointer[vidMap]
- Updated all cache access to use Load() and Store() atomic operations
- Updated shallowClone, GetLocations, deleteLocation, deleteEcLocation
- Updated resetVidMap to use atomic operations for cache trimming

weed/wdclient/masterclient.go

@@ -584,15 +584,15 @@ func (mc *MasterClient) resetVidMap() {
 	tail := mc.vidMap.shallowClone()
 
 	nvm := newVidMap(tail.DataCenter)
-	nvm.cache = tail
+	nvm.cache.Store(tail)
 	mc.vidMap = nvm
 
 	//trim
-	for i := 0; i < mc.vidMapCacheSize && tail.cache != nil; i++ {
+	for i := 0; i < mc.vidMapCacheSize && tail.cache.Load() != nil; i++ {
 		if i == mc.vidMapCacheSize-1 {
-			tail.cache = nil
+			tail.cache.Store(nil)
 		} else {
-			tail = tail.cache
+			tail = tail.cache.Load()
 		}
 	}
 }

weed/wdclient/vid_map.go

@@ -41,7 +41,7 @@ type vidMap struct {
 	ecVid2Locations map[uint32][]Location
 	DataCenter      string
 	cursor          int32
-	cache           *vidMap
+	cache           atomic.Pointer[vidMap]
 }
 
 func newVidMap(dataCenter string) *vidMap {
@@ -56,12 +56,16 @@ func newVidMap(dataCenter string) *vidMap {
 // shallowClone creates a shallow copy of the vidMap for use in cache chaining.
 // The caller is responsible for ensuring thread safety.
 func (vc *vidMap) shallowClone() *vidMap {
-	return &vidMap{
+	newMap := &vidMap{
 		vid2Locations:   vc.vid2Locations,
 		ecVid2Locations: vc.ecVid2Locations,
 		DataCenter:      vc.DataCenter,
-		cache:           vc.cache,
 	}
+	// Atomically copy the cache pointer
+	if cachedMap := vc.cache.Load(); cachedMap != nil {
+		newMap.cache.Store(cachedMap)
+	}
+	return newMap
 }
 
 func (vc *vidMap) getLocationIndex(length int) (int, error) {
@@ -146,8 +150,8 @@ func (vc *vidMap) GetLocations(vid uint32) (locations []Location, found bool) {
 		return locations, found
 	}
 
-	if vc.cache != nil {
-		return vc.cache.GetLocations(vid)
+	if cachedMap := vc.cache.Load(); cachedMap != nil {
+		return cachedMap.GetLocations(vid)
 	}
 
 	return nil, false
@@ -223,8 +227,8 @@ func (vc *vidMap) addEcLocation(vid uint32, location Location) {
 }
 
 func (vc *vidMap) deleteLocation(vid uint32, location Location) {
-	if vc.cache != nil {
-		vc.cache.deleteLocation(vid, location)
+	if cachedMap := vc.cache.Load(); cachedMap != nil {
+		cachedMap.deleteLocation(vid, location)
 	}
 
 	vc.Lock()
@@ -246,8 +250,8 @@ func (vc *vidMap) deleteLocation(vid uint32, location Location) {
 }
 
 func (vc *vidMap) deleteEcLocation(vid uint32, location Location) {
-	if vc.cache != nil {
-		vc.cache.deleteLocation(vid, location)
+	if cachedMap := vc.cache.Load(); cachedMap != nil {
+		cachedMap.deleteLocation(vid, location)
 	}
 
 	vc.Lock()