From bb31462b52d24bc7ebf54266b45801c198685f70 Mon Sep 17 00:00:00 2001
From: divinerapier <poriter.coco@gmail.com>
Date: Fri, 13 Sep 2019 20:06:02 +0800
Subject: [PATCH] fix: thread unsafe

Signed-off-by: divinerapier <poriter.coco@gmail.com>
---
 weed/wdclient/vid_map.go      | 26 +++++++++---
 weed/wdclient/vid_map_test.go | 77 +++++++++++++++++++++++++++++++++++
 2 files changed, 98 insertions(+), 5 deletions(-)
 create mode 100644 weed/wdclient/vid_map_test.go

diff --git a/weed/wdclient/vid_map.go b/weed/wdclient/vid_map.go
index 01d9cdaed..7a3f50aad 100644
--- a/weed/wdclient/vid_map.go
+++ b/weed/wdclient/vid_map.go
@@ -3,11 +3,11 @@ package wdclient
 import (
 	"errors"
 	"fmt"
-	"math/rand"
+	"math"
 	"strconv"
 	"strings"
 	"sync"
-	"time"
+	"sync/atomic"
 
 	"github.com/chrislusf/seaweedfs/weed/glog"
 )
@@ -20,16 +20,27 @@ type Location struct {
 type vidMap struct {
 	sync.RWMutex
 	vid2Locations map[uint32][]Location
-	r             *rand.Rand
+
+	cursor int64
 }
 
 func newVidMap() vidMap {
 	return vidMap{
 		vid2Locations: make(map[uint32][]Location),
-		r:             rand.New(rand.NewSource(time.Now().UnixNano())),
+		cursor:        -1,
 	}
 }
 
+func (vc *vidMap) getLocationIndex(length int64) (int64, error) {
+	if length <= 0 {
+		return 0, fmt.Errorf("invalid length: %d", length)
+	}
+	if atomic.LoadInt64(&vc.cursor) == math.MaxInt64 {
+		atomic.CompareAndSwapInt64(&vc.cursor, math.MaxInt64, -1)
+	}
+	return atomic.AddInt64(&vc.cursor, 1) % length, nil
+}
+
 func (vc *vidMap) LookupVolumeServerUrl(vid string) (serverUrl string, err error) {
 	id, err := strconv.Atoi(vid)
 	if err != nil {
@@ -94,7 +105,12 @@ func (vc *vidMap) GetRandomLocation(vid uint32) (serverUrl string, err error) {
 		return "", fmt.Errorf("volume %d not found", vid)
 	}
 
-	return locations[vc.r.Intn(len(locations))].Url, nil
+	index, err := vc.getLocationIndex(int64(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) {
diff --git a/weed/wdclient/vid_map_test.go b/weed/wdclient/vid_map_test.go
new file mode 100644
index 000000000..ae4680e7a
--- /dev/null
+++ b/weed/wdclient/vid_map_test.go
@@ -0,0 +1,77 @@
+package wdclient
+
+import (
+	"fmt"
+	"math"
+	"testing"
+)
+
+func TestLocationIndex(t *testing.T) {
+	vm := vidMap{}
+	// test must be failed
+	mustFailed := func(length int64) {
+		_, err := vm.getLocationIndex(length)
+		if err == nil {
+			t.Errorf("length %d must be failed", length)
+		}
+		if err.Error() != fmt.Sprintf("invalid length: %d", length) {
+			t.Errorf("length %d must be failed. error: %v", length, err)
+		}
+	}
+
+	mustFailed(-1)
+	mustFailed(0)
+
+	mustOk := func(length, cursor, expect int64) {
+		if length <= 0 {
+			t.Fatal("please don't do this")
+		}
+		vm.cursor = cursor
+		got, err := vm.getLocationIndex(length)
+		if err != nil {
+			t.Errorf("length: %d, why? %v\n", length, err)
+			return
+		}
+		if got != expect {
+			t.Errorf("cursor: %d, length: %d, expect: %d, got: %d\n", cursor, length, expect, got)
+			return
+		}
+	}
+
+	for i := int64(-1); i < 100; i++ {
+		mustOk(7, i, (i+1)%7)
+	}
+
+	// when cursor reaches MaxInt64
+	mustOk(7, math.MaxInt64, 0)
+
+	// test with constructor
+	vm = newVidMap()
+	length := int64(7)
+	for i := int64(0); i < 100; i++ {
+		got, err := vm.getLocationIndex(length)
+		if err != nil {
+			t.Errorf("length: %d, why? %v\n", length, err)
+			return
+		}
+		if got != i%length {
+			t.Errorf("length: %d, i: %d, got: %d\n", length, i, got)
+		}
+	}
+}
+
+func BenchmarkLocationIndex(b *testing.B) {
+	b.SetParallelism(8)
+	vm := vidMap{
+		cursor: math.MaxInt64 - 10000,
+	}
+	b.ResetTimer()
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			_, err := vm.getLocationIndex(3)
+			if err != nil {
+				b.Error(err)
+			}
+		}
+	})
+}