[WIP/RFC] Pointer indirection

blob.go

@@ -60,8 +60,13 @@ type BlobCallbackData struct {
 }
 
 //export blobChunkCb
-func blobChunkCb(buffer *C.char, maxLen C.size_t, payload unsafe.Pointer) int {
-	data := (*BlobCallbackData)(payload)
+func blobChunkCb(buffer *C.char, maxLen C.size_t, handle unsafe.Pointer) int {
+	payload := pointerHandles.Get(handle)
+	data, ok := payload.(*BlobCallbackData)
+	if !ok {
+		panic("could not retrieve blob callback data")
+	}
+
 	goBuf, err := data.Callback(int(maxLen))
 	if err == io.EOF {
 		return 0
@@ -83,8 +88,12 @@ func (repo *Repository) CreateBlobFromChunks(hintPath string, callback BlobChunk
 		defer C.free(unsafe.Pointer(chintPath))
 	}
 	oid := C.git_oid{}
+
 	payload := &BlobCallbackData{Callback: callback}
-	ecode := C._go_git_blob_create_fromchunks(&oid, repo.ptr, chintPath, unsafe.Pointer(payload))
+	handle := pointerHandles.Track(payload)
+	defer pointerHandles.Untrack(handle)
+
+	ecode := C._go_git_blob_create_fromchunks(&oid, repo.ptr, chintPath, handle)
 	if payload.Error != nil {
 		return nil, payload.Error
 	}

diff.go

@@ -265,16 +265,24 @@ func (diff *Diff) ForEach(cbFile DiffForEachFileCallback, detail DiffDetail) err
 	data := &diffForEachData{
 		FileCallback: cbFile,
 	}
-	ecode := C._go_git_diff_foreach(diff.ptr, 1, intHunks, intLines, unsafe.Pointer(data))
+
+	handle := pointerHandles.Track(data)
+	defer pointerHandles.Untrack(handle)
+
+	ecode := C._go_git_diff_foreach(diff.ptr, 1, intHunks, intLines, handle)
 	if ecode < 0 {
 		return data.Error
 	}
 	return nil
 }
 
 //export diffForEachFileCb
-func diffForEachFileCb(delta *C.git_diff_delta, progress C.float, payload unsafe.Pointer) int {
-	data := (*diffForEachData)(payload)
+func diffForEachFileCb(delta *C.git_diff_delta, progress C.float, handle unsafe.Pointer) int {
+	payload := pointerHandles.Get(handle)
+	data, ok := payload.(*diffForEachData)
+	if !ok {
+		panic("could not retrieve data for handle")
+	}
 
 	data.HunkCallback = nil
 	if data.FileCallback != nil {
@@ -292,8 +300,12 @@ func diffForEachFileCb(delta *C.git_diff_delta, progress C.float, payload unsafe
 type DiffForEachHunkCallback func(DiffHunk) (DiffForEachLineCallback, error)
 
 //export diffForEachHunkCb
-func diffForEachHunkCb(delta *C.git_diff_delta, hunk *C.git_diff_hunk, payload unsafe.Pointer) int {
-	data := (*diffForEachData)(payload)
+func diffForEachHunkCb(delta *C.git_diff_delta, hunk *C.git_diff_hunk, handle unsafe.Pointer) int {
+	payload := pointerHandles.Get(handle)
+	data, ok := payload.(*diffForEachData)
+	if !ok {
+		panic("could not retrieve data for handle")
+	}
 
 	data.LineCallback = nil
 	if data.HunkCallback != nil {
@@ -311,9 +323,12 @@ func diffForEachHunkCb(delta *C.git_diff_delta, hunk *C.git_diff_hunk, payload u
 type DiffForEachLineCallback func(DiffLine) error
 
 //export diffForEachLineCb
-func diffForEachLineCb(delta *C.git_diff_delta, hunk *C.git_diff_hunk, line *C.git_diff_line, payload unsafe.Pointer) int {
-
-	data := (*diffForEachData)(payload)
+func diffForEachLineCb(delta *C.git_diff_delta, hunk *C.git_diff_hunk, line *C.git_diff_line, handle unsafe.Pointer) int {
+	payload := pointerHandles.Get(handle)
+	data, ok := payload.(*diffForEachData)
+	if !ok {
+		panic("could not retrieve data for handle")
+	}
 
 	err := data.LineCallback(diffLineFromC(delta, hunk, line))
 	if err != nil {
@@ -479,9 +494,15 @@ type diffNotifyData struct {
 }
 
 //export diffNotifyCb
-func diffNotifyCb(_diff_so_far unsafe.Pointer, delta_to_add *C.git_diff_delta, matched_pathspec *C.char, payload unsafe.Pointer) int {
+func diffNotifyCb(_diff_so_far unsafe.Pointer, delta_to_add *C.git_diff_delta, matched_pathspec *C.char, handle unsafe.Pointer) int {
 	diff_so_far := (*C.git_diff)(_diff_so_far)
-	data := (*diffNotifyData)(payload)
+
+	payload := pointerHandles.Get(handle)
+	data, ok := payload.(*diffNotifyData)
+	if !ok {
+		panic("could not retrieve data for handle")
+	}
+
 	if data != nil {
 		if data.Diff == nil {
 			data.Diff = newDiffFromC(diff_so_far)
@@ -507,6 +528,7 @@ func diffOptionsToC(opts *DiffOptions) (copts *C.git_diff_options, notifyData *d
 		notifyData = &diffNotifyData{
 			Callback: opts.NotifyCallback,
 		}
+
 		if opts.Pathspec != nil {
 			cpathspec.count = C.size_t(len(opts.Pathspec))
 			cpathspec.strings = makeCStringsFromStrings(opts.Pathspec)
@@ -527,7 +549,7 @@ func diffOptionsToC(opts *DiffOptions) (copts *C.git_diff_options, notifyData *d
 
 		if opts.NotifyCallback != nil {
 			C._go_git_setup_diff_notify_callbacks(copts)
-			copts.notify_payload = unsafe.Pointer(notifyData)
+			copts.notify_payload = pointerHandles.Track(notifyData)
 		}
 	}
 	return
@@ -539,6 +561,9 @@ func freeDiffOptions(copts *C.git_diff_options) {
 		freeStrarray(&cpathspec)
 		C.free(unsafe.Pointer(copts.old_prefix))
 		C.free(unsafe.Pointer(copts.new_prefix))
+		if copts.notify_payload != nil {
+			pointerHandles.Untrack(copts.notify_payload)
+		}
 	}
 }
 

git.go

@@ -93,7 +93,11 @@ var (
 	ErrInvalid = errors.New("Invalid state for operation")
 )
 
+var pointerHandles *HandleList
+
 func init() {
+	pointerHandles = NewHandleList()
+
 	C.git_libgit2_init()
 
 	// This is not something we should be doing, as we may be

handles.go

@@ -0,0 +1,84 @@
+package git
+
+import (
+	"fmt"
+	"sync"
+	"unsafe"
+)
+
+type HandleList struct {
+	sync.RWMutex
+	// stores the Go pointers
+	handles []interface{}
+	// indicates which indices are in use
+	set map[int]bool
+}
+
+func NewHandleList() *HandleList {
+	return &HandleList{
+		handles: make([]interface{}, 5),
+		set:     make(map[int]bool),
+	}
+}
+
+// findUnusedSlot finds the smallest-index empty space in our
+// list. You must only run this function while holding a write lock.
+func (v *HandleList) findUnusedSlot() int {
+	for i := 1; i < len(v.handles); i++ {
+		isUsed := v.set[i]
+		if !isUsed {
+			return i
+		}
+	}
+
+	// reaching here means we've run out of entries so append and
+	// return the new index, which is equal to the old length.
+	slot := len(v.handles)
+	v.handles = append(v.handles, nil)
+
+	return slot
+}
+
+// Track adds the given pointer to the list of pointers to track and
+// returns a pointer value which can be passed to C as an opaque
+// pointer.
+func (v *HandleList) Track(pointer interface{}) unsafe.Pointer {
+	v.Lock()
+
+	slot := v.findUnusedSlot()
+	v.handles[slot] = pointer
+	v.set[slot] = true
+
+	v.Unlock()
+
+	return unsafe.Pointer(&slot)
+}
+
+// Untrack stops tracking the pointer given by the handle
+func (v *HandleList) Untrack(handle unsafe.Pointer) {
+	slot := *(*int)(handle)
+
+	v.Lock()
+
+	v.handles[slot] = nil
+	delete(v.set, slot)
+
+	v.Unlock()
+}
+
+// Get retrieves the pointer from the given handle
+func (v *HandleList) Get(handle unsafe.Pointer) interface{} {
+	slot := *(*int)(handle)
+
+	v.RLock()
+
+	if _, ok := v.set[slot]; !ok {
+		panic(fmt.Sprintf("invalid pointer handle: %p", handle))
+	}
+
+	ptr := v.handles[slot]
+
+	v.RUnlock()
+
+	return ptr
+}

index.go

@@ -162,16 +162,17 @@ func (v *Index) AddAll(pathspecs []string, flags IndexAddOpts, callback IndexMat
 	runtime.LockOSThread()
 	defer runtime.UnlockOSThread()
 
-	var cb *IndexMatchedPathCallback
+	var handle unsafe.Pointer
 	if callback != nil {
-		cb = &callback
+		handle = pointerHandles.Track(callback)
+		defer pointerHandles.Untrack(handle)
 	}
 
 	ret := C._go_git_index_add_all(
 		v.ptr,
 		&cpathspecs,
 		C.uint(flags),
-		unsafe.Pointer(cb),
+		handle,
 	)
 	if ret < 0 {
 		return MakeGitError(ret)
@@ -188,15 +189,16 @@ func (v *Index) UpdateAll(pathspecs []string, callback IndexMatchedPathCallback)
 	runtime.LockOSThread()
 	defer runtime.UnlockOSThread()
 
-	var cb *IndexMatchedPathCallback
+	var handle unsafe.Pointer
 	if callback != nil {
-		cb = &callback
+		handle = pointerHandles.Track(callback)
+		defer pointerHandles.Untrack(handle)
 	}
 
 	ret := C._go_git_index_update_all(
 		v.ptr,
 		&cpathspecs,
-		unsafe.Pointer(cb),
+		handle,
 	)
 	if ret < 0 {
 		return MakeGitError(ret)
@@ -213,15 +215,16 @@ func (v *Index) RemoveAll(pathspecs []string, callback IndexMatchedPathCallback)
 	runtime.LockOSThread()
 	defer runtime.UnlockOSThread()
 
-	var cb *IndexMatchedPathCallback
+	var handle unsafe.Pointer
 	if callback != nil {
-		cb = &callback
+		handle = pointerHandles.Track(callback)
+		defer pointerHandles.Untrack(handle)
 	}
 
 	ret := C._go_git_index_remove_all(
 		v.ptr,
 		&cpathspecs,
-		unsafe.Pointer(cb),
+		handle,
 	)
 	if ret < 0 {
 		return MakeGitError(ret)
@@ -231,8 +234,11 @@ func (v *Index) RemoveAll(pathspecs []string, callback IndexMatchedPathCallback)
 
 //export indexMatchedPathCallback
 func indexMatchedPathCallback(cPath, cMatchedPathspec *C.char, payload unsafe.Pointer) int {
-	callback := (*IndexMatchedPathCallback)(payload)
-	return (*callback)(C.GoString(cPath), C.GoString(cMatchedPathspec))
+	if callback, ok := pointerHandles.Get(payload).(IndexMatchedPathCallback); ok {
+		return callback(C.GoString(cPath), C.GoString(cMatchedPathspec))
+	} else {
+		panic("invalid matched path callback")
+	}
 }
 
 func (v *Index) RemoveByPath(path string) error {

odb.go

@@ -98,8 +98,12 @@ type foreachData struct {
 }
 
 //export odbForEachCb
-func odbForEachCb(id *C.git_oid, payload unsafe.Pointer) int {
-	data := (*foreachData)(payload)
+func odbForEachCb(id *C.git_oid, handle unsafe.Pointer) int {
+	data, ok := pointerHandles.Get(handle).(*foreachData)
+
+	if !ok {
+		panic("could not retrieve handle")
+	}
 
 	err := data.callback(newOidFromC(id))
 	if err != nil {
@@ -119,7 +123,10 @@ func (v *Odb) ForEach(callback OdbForEachCallback) error {
 	runtime.LockOSThread()
 	defer runtime.UnlockOSThread()
 
-	ret := C._go_git_odb_foreach(v.ptr, unsafe.Pointer(&data))
+	handle := pointerHandles.Track(&data)
+	defer pointerHandles.Untrack(handle)
+
+	ret := C._go_git_odb_foreach(v.ptr, handle)
 	if ret == C.GIT_EUSER {
 		return data.err
 	} else if ret < 0 {

odb_test.go

@@ -81,7 +81,7 @@ func TestOdbForeach(t *testing.T) {
 
 	checkFatal(t, err)
 	if count != expect {
-		t.Fatalf("Expected %v objects, got %v")
+		t.Fatalf("Expected %v objects, got %v", expect, count)
 	}
 
 	expect = 1

packbuilder.go

@@ -110,8 +110,13 @@ type packbuilderCbData struct {
 }
 
 //export packbuilderForEachCb
-func packbuilderForEachCb(buf unsafe.Pointer, size C.size_t, payload unsafe.Pointer) int {
-	data := (*packbuilderCbData)(payload)
+func packbuilderForEachCb(buf unsafe.Pointer, size C.size_t, handle unsafe.Pointer) int {
+	payload := pointerHandles.Get(handle)
+	data, ok := payload.(*packbuilderCbData)
+	if !ok {
+		panic("could not get packbuilder CB data")
+	}
+
 	slice := C.GoBytes(buf, C.int(size))
 
 	err := data.callback(slice)
@@ -130,11 +135,13 @@ func (pb *Packbuilder) ForEach(callback PackbuilderForeachCallback) error {
 		callback: callback,
 		err:      nil,
 	}
+	handle := pointerHandles.Track(&data)
+	defer pointerHandles.Untrack(handle)
 
 	runtime.LockOSThread()
 	defer runtime.UnlockOSThread()
 
-	err := C._go_git_packbuilder_foreach(pb.ptr, unsafe.Pointer(&data))
+	err := C._go_git_packbuilder_foreach(pb.ptr, handle)
 	if err == C.GIT_EUSER {
 		return data.err
 	}