From 73020a3110c13c39a0bcc21499a2d2fd281c39fb Mon Sep 17 00:00:00 2001
From: Tim Ebringer <tde@slowdogs.com.au>
Date: Wed, 19 Jul 2017 11:17:18 -0400
Subject: [PATCH] Bool is not atomic

The Go race detector doesn't like concurrent access to bool. This change
moves the bool to use atomicBool, and extends atomicBool with the swap()
method, to handle conditional use.
---
 file.go | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/file.go b/file.go
index 9c9ee5d2..2a311d1f 100644
--- a/file.go
+++ b/file.go
@@ -23,6 +23,13 @@ type atomicBool int32
 func (b *atomicBool) isSet() bool { return atomic.LoadInt32((*int32)(b)) != 0 }
 func (b *atomicBool) setFalse()   { atomic.StoreInt32((*int32)(b), 0) }
 func (b *atomicBool) setTrue()    { atomic.StoreInt32((*int32)(b), 1) }
+func (b *atomicBool) swap(new bool) bool {
+	var newInt int32
+	if new {
+		newInt = 1
+	}
+	return atomic.SwapInt32((*int32)(b), newInt) == 1
+}
 
 const (
 	cFILE_SKIP_COMPLETION_PORT_ON_SUCCESS = 1
@@ -71,7 +78,7 @@ func initIo() {
 type win32File struct {
 	handle        syscall.Handle
 	wg            sync.WaitGroup
-	closing       bool
+	closing       atomicBool
 	readDeadline  deadlineHandler
 	writeDeadline deadlineHandler
 }
@@ -107,9 +114,9 @@ func MakeOpenFile(h syscall.Handle) (io.ReadWriteCloser, error) {
 
 // closeHandle closes the resources associated with a Win32 handle
 func (f *win32File) closeHandle() {
-	if !f.closing {
+	// Atomically set that we are closing, releasing the resources only once.
+	if !f.closing.swap(true) {
 		// cancel all IO and wait for it to complete
-		f.closing = true
 		cancelIoEx(f.handle, nil)
 		f.wg.Wait()
 		// at this point, no new IO can start
@@ -127,7 +134,7 @@ func (f *win32File) Close() error {
 // prepareIo prepares for a new IO operation.
 // The caller must call f.wg.Done() when the IO is finished, prior to Close() returning.
 func (f *win32File) prepareIo() (*ioOperation, error) {
-	if f.closing {
+	if f.closing.isSet() {
 		return nil, ErrFileClosed
 	}
 	f.wg.Add(1)
@@ -159,7 +166,7 @@ func (f *win32File) asyncIo(c *ioOperation, d *deadlineHandler, bytes uint32, er
 		return int(bytes), err
 	}
 
-	if f.closing {
+	if f.closing.isSet() {
 		cancelIoEx(f.handle, &c.o)
 	}
 
@@ -175,7 +182,7 @@ func (f *win32File) asyncIo(c *ioOperation, d *deadlineHandler, bytes uint32, er
 	case r = <-c.ch:
 		err = r.err
 		if err == syscall.ERROR_OPERATION_ABORTED {
-			if f.closing {
+			if f.closing.isSet() {
 				err = ErrFileClosed
 			}
 		}