syscall: fix data races in LazyDLL/LazyProc

src/pkg/syscall/dll_windows.go

Index: src/pkg/syscall/dll_windows.go 
=================================================================== 
--- a/src/pkg/syscall/dll_windows.go 
+++ b/src/pkg/syscall/dll_windows.go 
@@ -6,6 +6,8 @@ 
 
 import ( 
	"sync" 
+	"sync/atomic" 
+	"unsafe" 
 ) 
 
 // DLLError describes reasons for DLL load failures. 
@@ -166,7 +168,7 @@ 
 // Load loads DLL file d.Name into memory. It returns an error if fails. 
 // Load will not try to load DLL, if it is already loaded into memory. 
 func (d *LazyDLL) Load() error { 
-	if d.dll == nil { 
+	if atomic.LoadPointer((*unsafe.Pointer)(unsafe.Pointer(&d.dll))) == nil { 
	d.mu.Lock() 
	defer d.mu.Unlock() 
	if d.dll == nil { 
@@ -174,7 +176,7 @@ 
	if e != nil { 
	return e 
	} 
-	d.dll = dll 
+	atomic.StorePointer((*unsafe.Pointer)(unsafe.Pointer(&d.dll)), unsafe.Pointer(dll)) 

[brainman, 2012/11/07 03:50:03]

I do not think you need to change that line. d.mu.Lock up above should protect code executing here. 

	} 
	} 
	return nil 
@@ -217,7 +219,7 @@ 
 // an error if search fails. Find will not search procedure, 
 // if it is already found and loaded into memory. 
 func (p *LazyProc) Find() error { 
-	if p.proc == nil { 
+	if atomic.LoadPointer((*unsafe.Pointer)(unsafe.Pointer(&p.proc))) == nil { 
	p.mu.Lock() 
	defer p.mu.Unlock() 
	if p.proc == nil { 
@@ -229,7 +231,7 @@ 
	if e != nil { 
	return e 
	} 
-	p.proc = proc 
+	atomic.StorePointer((*unsafe.Pointer)(unsafe.Pointer(&p.proc)), unsafe.Pointer(proc)) 

[brainman, 2012/11/07 03:50:03]

Same. Do not change that line. 

	} 
	} 
	return nil