Revert "stickiness: avoid using unsafe (grpc#2023)"

This reverts commit 7263089.

picker_wrapper.go

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