cmd/go/internal/renameio: mask spurious "Access is denied" errors on Windows

Fixes #31247

Change-Id: I85a760a5d36ae835c97a13f980804d06b658857e
Reviewed-on: https://go-review.googlesource.com/c/go/+/172418
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/go/internal/renameio/renameio.go

@@ -11,6 +11,9 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"runtime"
+	"strings"
+	"time"
 )
 
 const patternSuffix = "*.tmp"
@@ -59,5 +62,22 @@ func WriteToFile(filename string, data io.Reader) (err error) {
 	if err := f.Close(); err != nil {
 		return err
 	}
-	return os.Rename(f.Name(), filename)
+
+	var start time.Time
+	for {
+		err := os.Rename(f.Name(), filename)
+		if err == nil || runtime.GOOS != "windows" || !strings.HasSuffix(err.Error(), "Access is denied.") {
+			return err
+		}
+
+		// Windows seems to occasionally trigger spurious "Access is denied" errors
+		// here (see golang.org/issue/31247). We're not sure why. It's probably
+		// worth a little extra latency to avoid propagating the spurious errors.
+		if start.IsZero() {
+			start = time.Now()
+		} else if time.Since(start) >= 500*time.Millisecond {
+			return err
+		}
+		time.Sleep(5 * time.Millisecond)
+	}
 }