tree: use HandleList for C function callbacks.

Author: pks-t

tree.go

@@ -93,19 +93,25 @@ type TreeWalkCallback func(string, *TreeEntry) int
 func CallbackGitTreeWalk(_root unsafe.Pointer, _entry unsafe.Pointer, ptr unsafe.Pointer) C.int {
 	root := C.GoString((*C.char)(_root))
 	entry := (*C.git_tree_entry)(_entry)
-	callback := *(*TreeWalkCallback)(ptr)
 
-	return C.int(callback(root, newTreeEntry(entry)))
+	if callback, ok := pointerHandles.Get(ptr).(TreeWalkCallback); ok {
+		return C.int(callback(root, newTreeEntry(entry)))
+	} else {
+		return C.int(-1)
+	}
 }
 
 func (t Tree) Walk(callback TreeWalkCallback) error {
 	runtime.LockOSThread()
 	defer runtime.UnlockOSThread()
 
+	ptr := pointerHandles.Track(callback)
+	defer pointerHandles.Untrack(ptr)
+
 	err := C._go_git_treewalk(
 		t.cast_ptr,
 		C.GIT_TREEWALK_PRE,
-		unsafe.Pointer(&callback),
+		ptr,
 	)
 
 	if err < 0 {