stickiness: avoid using unsafe (grpc#2023)

App Engine doesn't allow use of unsafe.

picker_wrapper.go

@@ -22,7 +22,6 @@ import (
  "io"
  "sync"
  "sync/atomic"
- "unsafe"
 
  "golang.org/x/net/context"
  "google.golang.org/grpc/balancer"
@@ -47,7 +46,7 @@ type pickerWrapper struct {
  connErrMu sync.Mutex
  connErr error
 
- stickinessMDKey unsafe.Pointer
+ stickinessMDKey atomic.Value
  stickiness *stickyStore
 }
 
@@ -73,18 +72,17 @@ func (bp *pickerWrapper) connectionError() error {
 }
 
 func (bp *pickerWrapper) updateStickinessMDKey(newKey string) {
- oldKeyUnsafePtr := atomic.SwapPointer(&bp.stickinessMDKey, unsafe.Pointer(&newKey))
- if ptr := (*string)(oldKeyUnsafePtr); ptr == nil || *ptr != newKey {
+ // No need to check ok because mdKey == "" if ok == false.
+ if oldKey, _ := bp.stickinessMDKey.Load().(string); oldKey != newKey {
+ bp.stickinessMDKey.Store(newKey)
  bp.stickiness.reset(newKey)
  }
 }
 
 func (bp *pickerWrapper) getStickinessMDKey() string {
- mdKeyPtr := (*string)(atomic.LoadPointer(&bp.stickinessMDKey))
- if mdKeyPtr != nil {
- return *mdKeyPtr
- }
- return ""
+ // No need to check ok because mdKey == "" if ok == false.
+ mdKey, _ := bp.stickinessMDKey.Load().(string)
+ return mdKey
 }
 
 func (bp *pickerWrapper) clearStickinessState() {