context: convert goroutines to atomic type

Change-Id: I021fbc9786a3e3f858770fe3e109a0de487390d8
Reviewed-on: https://go-review.googlesource.com/c/go/+/426089
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Run-TryBot: xie cui <523516579@qq.com>
Reviewed-by: Damien Neil <dneil@google.com>

src/context/context.go

@@ -244,7 +244,7 @@ func newCancelCtx(parent Context) cancelCtx {
 }
 
 // goroutines counts the number of goroutines ever created; for testing.
-var goroutines int32
+var goroutines atomic.Int32
 
 // propagateCancel arranges for child to be canceled when parent is.
 func propagateCancel(parent Context, child canceler) {
@@ -274,7 +274,7 @@ func propagateCancel(parent Context, child canceler) {
 		}
 		p.mu.Unlock()
 	} else {
-		atomic.AddInt32(&goroutines, +1)
+		goroutines.Add(1)
 		go func() {
 			select {
 			case <-parent.Done():

src/context/context_test.go

@@ -10,7 +10,6 @@ import (
 	"runtime"
 	"strings"
 	"sync"
-	"sync/atomic"
 	"time"
 )
 
@@ -723,17 +722,17 @@ func (d *myDoneCtx) Done() <-chan struct{} {
 }
 
 func XTestCustomContextGoroutines(t testingT) {
-	g := atomic.LoadInt32(&goroutines)
+	g := goroutines.Load()
 	checkNoGoroutine := func() {
 		t.Helper()
-		now := atomic.LoadInt32(&goroutines)
+		now := goroutines.Load()
 		if now != g {
 			t.Fatalf("%d goroutines created", now-g)
 		}
 	}
 	checkCreatedGoroutine := func() {
 		t.Helper()
-		now := atomic.LoadInt32(&goroutines)
+		now := goroutines.Load()
 		if now != g+1 {
 			t.Fatalf("%d goroutines created, want 1", now-g)
 		}