1 files changed, 47 insertions, 12 deletions

diff --git a/weed/wdclient/vid_map.go b/weed/wdclient/vid_map.go
index aef29f56f..97df49cb6 100644
--- a/weed/wdclient/vid_map.go
+++ b/weed/wdclient/vid_map.go
@@ -3,14 +3,18 @@ package wdclient
 import (
 	"errors"
 	"fmt"
-	"math/rand"
 	"strconv"
 	"strings"
 	"sync"
+	"sync/atomic"
 
 	"github.com/chrislusf/seaweedfs/weed/glog"
 )
 
+const (
+	maxCursorIndex = 4096
+)
+
 type Location struct {
 	Url       string `json:"url,omitempty"`
 	PublicUrl string `json:"publicUrl,omitempty"`
@@ -19,14 +23,27 @@ type Location struct {
 type vidMap struct {
 	sync.RWMutex
 	vid2Locations map[uint32][]Location
+
+	cursor int32
 }
 
 func newVidMap() vidMap {
 	return vidMap{
 		vid2Locations: make(map[uint32][]Location),
+		cursor:        -1,
 	}
 }
 
+func (vc *vidMap) getLocationIndex(length int) (int, error) {
+	if length <= 0 {
+		return 0, fmt.Errorf("invalid length: %d", length)
+	}
+	if atomic.LoadInt32(&vc.cursor) == maxCursorIndex {
+		atomic.CompareAndSwapInt32(&vc.cursor, maxCursorIndex, -1)
+	}
+	return int(atomic.AddInt32(&vc.cursor, 1)) % length, nil
+}
+
 func (vc *vidMap) LookupVolumeServerUrl(vid string) (serverUrl string, err error) {
 	id, err := strconv.Atoi(vid)
 	if err != nil {
@@ -34,12 +51,7 @@ func (vc *vidMap) LookupVolumeServerUrl(vid string) (serverUrl string, err error
 		return "", err
 	}
 
-	locations := vc.GetLocations(uint32(id))
-	if len(locations) == 0 {
-		return "", fmt.Errorf("volume %d not found", id)
-	}
-
-	return locations[rand.Intn(len(locations))].Url, nil
+	return vc.GetRandomLocation(uint32(id))
 }
 
 func (vc *vidMap) LookupFileId(fileId string) (fullUrl string, err error) {
@@ -66,20 +78,42 @@ func (vc *vidMap) LookupVolumeServer(fileId string) (volumeServer string, err er
 	return serverUrl, nil
 }
 
-func (vc *vidMap) GetVidLocations(vid string) (locations []Location) {
+func (vc *vidMap) GetVidLocations(vid string) (locations []Location, err error) {
 	id, err := strconv.Atoi(vid)
 	if err != nil {
 		glog.V(1).Infof("Unknown volume id %s", vid)
-		return nil
+		return nil, fmt.Errorf("Unknown volume id %s", vid)
+	}
+	foundLocations, found := vc.GetLocations(uint32(id))
+	if found {
+		return foundLocations, nil
 	}
-	return vc.GetLocations(uint32(id))
+	return nil, fmt.Errorf("volume id %s not found", vid)
 }
 
-func (vc *vidMap) GetLocations(vid uint32) (locations []Location) {
+func (vc *vidMap) GetLocations(vid uint32) (locations []Location, found bool) {
 	vc.RLock()
 	defer vc.RUnlock()
 
-	return vc.vid2Locations[vid]
+	locations, found = vc.vid2Locations[vid]
+	return
+}
+
+func (vc *vidMap) GetRandomLocation(vid uint32) (serverUrl string, err error) {
+	vc.RLock()
+	defer vc.RUnlock()
+
+	locations := vc.vid2Locations[vid]
+	if len(locations) == 0 {
+		return "", fmt.Errorf("volume %d not found", vid)
+	}
+
+	index, err := vc.getLocationIndex(len(locations))
+	if err != nil {
+		return "", fmt.Errorf("volume %d: %v", vid, err)
+	}
+
+	return locations[index].Url, nil
 }
 
 func (vc *vidMap) addLocation(vid uint32, location Location) {
@@ -114,6 +148,7 @@ func (vc *vidMap) deleteLocation(vid uint32, location Location) {
 	for i, loc := range locations {
 		if loc.Url == location.Url {
 			vc.vid2Locations[vid] = append(locations[0:i], locations[i+1:]...)
+			break
 		}
 	}