cmd/go: use runtime.AddCleanup instead of runtime.SetFinalizer

Replace the usage of runtime.SetFinalizer with runtime.AddCleanup.
This changes a test and how when the Go command panics when a file is
left locked.

Updates #70907

Change-Id: I8d8c56d16486728f9bd4b910b81796ae506bda74
Reviewed-on: https://go-review.googlesource.com/c/go/+/640736
Reviewed-by: Sam Thanawalla <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: cagedmantis

src/cmd/go/internal/base/limit.go

@@ -52,7 +52,7 @@ func AcquireNet() (release func(), err error) {
 	}
 
 	checker := new(netTokenChecker)
-	runtime.SetFinalizer(checker, (*netTokenChecker).panicUnreleased)
+	cleanup := runtime.AddCleanup(checker, func(_ int) { panic("internal error: net token acquired but not released") }, 0)
 
 	return func() {
 		if checker.released {
@@ -62,7 +62,7 @@ func AcquireNet() (release func(), err error) {
 		if hasToken {
 			<-netLimitSem
 		}
-		runtime.SetFinalizer(checker, nil)
+		cleanup.Stop()
 	}, nil
 }
 
@@ -78,7 +78,3 @@ type netTokenChecker struct {
 	// “tiny allocator”.
 	unusedAvoidTinyAllocator string
 }
-
-func (c *netTokenChecker) panicUnreleased() {
-	panic("internal error: net token acquired but not released")
-}

src/cmd/go/internal/lockedfile/lockedfile.go

@@ -24,6 +24,8 @@ import (
 type File struct {
 	osFile
 	closed bool
+	// cleanup panics when the file is no longer referenced and it has not been closed.
+	cleanup runtime.Cleanup
 }
 
 // osFile embeds a *os.File while keeping the pointer itself unexported.
@@ -48,11 +50,11 @@ func OpenFile(name string, flag int, perm fs.FileMode) (*File, error) {
 	// Although the operating system will drop locks for open files when the go
 	// command exits, we want to hold locks for as little time as possible, and we
 	// especially don't want to leave a file locked after we're done with it. Our
-	// Close method is what releases the locks, so use a finalizer to report
+	// Close method is what releases the locks, so use a cleanup to report
 	// missing Close calls on a best-effort basis.
-	runtime.SetFinalizer(f, func(f *File) {
-		panic(fmt.Sprintf("lockedfile.File %s became unreachable without a call to Close", f.Name()))
-	})
+	f.cleanup = runtime.AddCleanup(f, func(fileName string) {
+		panic(fmt.Sprintf("lockedfile.File %s became unreachable without a call to Close", fileName))
+	}, f.Name())
 
 	return f, nil
 }
@@ -91,7 +93,7 @@ func (f *File) Close() error {
 	f.closed = true
 
 	err := closeFile(f.osFile.File)
-	runtime.SetFinalizer(f, nil)
+	f.cleanup.Stop()
 	return err
 }