convert cgo function pointer call to repeated iteration

main.go

@@ -68,15 +68,36 @@ func withBoltDBReference(b ObjectReference, fn func(db *bolt.DB) error) error {
 	return fn(ptrDB)
 }
 
+type CallResponse struct {
+	s string
+	e error
+}
+
+type NextCall struct {
+	content chan CallResponse
+}
+
 //export Bolt_ListBuckets
-func Bolt_ListBuckets(b ObjectReference, browse []string, ctx uintptr, withEach func(uintptr, string)) string {
-	if len(browse) == 0 {
-		return Bolt_ListBucketsAtRoot(b, ctx, withEach)
+func Bolt_ListBuckets(b ObjectReference, browse []string) ObjectReference {
+	pNC := &NextCall{
+		content: make(chan CallResponse, 0),
 	}
 
+	pNC_Ref := gms.Put(pNC)
+
+	go func() {
 		err := withBoltDBReference(b, func(db *bolt.DB) error {
 			return db.View(func(tx *bolt.Tx) error {
 
+				if len(browse) == 0 {
+					// Root-mode
+					return tx.ForEach(func(k []byte, _ *bolt.Bucket) error {
+						pNC.content <- CallResponse{s: string(k)}
+						return nil
+					})
+
+				} else {
+					// Nested-mode
 					bucket := tx.Bucket([]byte(browse[0]))
 					if bucket == nil {
 						return errors.New("Unknown bucket")
@@ -90,39 +111,59 @@ func Bolt_ListBuckets(b ObjectReference, browse []string, ctx uintptr, withEach
 					}
 
 					return bucket.ForEach(func(k, v []byte) error {
-
-				withEach(ctx, string(k))
+						pNC.content <- CallResponse{s: string(k)}
 						return nil
 					})
 
+				}
 			})
 		})
 
 		if err != nil {
-		return err.Error()
+			pNC.content <- CallResponse{e: err}
 		}
 
-	return ""
+		close(pNC.content)
+	}()
+
+	return pNC_Ref
+}
+
+const (
+	ERROR_AND_STOP_CALLING int = 100
+	ERROR_AND_KEEP_CALLING     = 101
+	FINISHED_OK                = 102
+	REAL_MESSAGE               = 103
+)
+
+//export GetNext
+func GetNext(oRef ObjectReference) (int, string) {
+	pNC_Iface, ok := gms.Get(oRef)
+	if !ok {
+		return ERROR_AND_STOP_CALLING, NullObjectReference.Error()
+	}
+
+	pNC, ok := pNC_Iface.(*NextCall)
+	if !ok {
+		return ERROR_AND_STOP_CALLING, NullObjectReference.Error()
+	}
+
+	cr, ok := <-pNC.content
+	if !ok {
+		gms.Delete(oRef)
+		return FINISHED_OK, ""
+	}
+
+	if cr.e != nil {
+		return ERROR_AND_KEEP_CALLING, cr.e.Error()
+	}
+
+	return REAL_MESSAGE, cr.s
 }
 
 //export Bolt_ListBucketsAtRoot
-func Bolt_ListBucketsAtRoot(b ObjectReference, ctx uintptr, withEach func(uintptr, string)) string {
-	err := withBoltDBReference(b, func(db *bolt.DB) error {
-		return db.View(func(tx *bolt.Tx) error {
-
-			return tx.ForEach(func(n []byte, bucket *bolt.Bucket) error {
-
-				withEach(ctx, string(n))
-				return nil
-			})
-
-		})
-	})
-
-	if err != nil {
-		return err.Error()
-	}
-	return ""
+func Bolt_ListBucketsAtRoot(b ObjectReference) ObjectReference {
+	return Bolt_ListBuckets(b, nil)
 }
 
 //export Bolt_Close

qbolt.h

@@ -68,9 +68,17 @@ struct Bolt_Open_return {
 
 extern struct Bolt_Open_return Bolt_Open(GoString p0, GoUint32 p1, GoInt64 p2);
 
-extern GoString Bolt_ListBuckets(GoInt64 p0, GoSlice p1, GoUintptr p2, void* p3);
+extern GoInt64 Bolt_ListBuckets(GoInt64 p0, GoSlice p1);
 
-extern GoString Bolt_ListBucketsAtRoot(GoInt64 p0, GoUintptr p1, void* p2);
+/* Return type for GetNext */
+struct GetNext_return {
+	GoInt r0;
+	GoString r1;
+};
+
+extern struct GetNext_return GetNext(GoInt64 p0);
+
+extern GoInt64 Bolt_ListBucketsAtRoot(GoInt64 p0);
 
 extern GoString Bolt_Close(GoInt64 p0);
 

qbolt/boltdb.cpp

@@ -23,32 +23,39 @@ BoltDB* BoltDB::createFrom(QString filePath, QString &errorOut)
     return ret;
 }
 
-template<typename T>
-struct Wrapper {
-    T t;
-};
-
-static void byteArrayCallback(void* ctx, GoString text) {
-    auto fn = static_cast<Wrapper<NameReciever>*>(ctx);
-    fn->t(QByteArray::fromRawData(text.p, text.n));
-}
+static const int ERROR_AND_STOP_CALLING = 100;
+static const int ERROR_AND_KEEP_CALLING = 101;
+static const int FINISHED_OK            = 102;
+static const int REAL_MESSAGE           = 103;
 
 bool BoltDB::listBucketsAtRoot(QString& errorOut, NameReciever cb)
 {
-    auto containerVar = Wrapper<NameReciever>{cb};
+    auto listJob = ::Bolt_ListBucketsAtRoot(this->gmsDbRef);
 
-    GoString err = ::Bolt_ListBucketsAtRoot(
-        this->gmsDbRef,
-        (GoUintptr)(&containerVar),
-        byteArrayCallback // -fpermissive
-    );
+    errorOut.clear();
 
-    if (err.n > 0) {
-        errorOut = QString(err.p);
-        return false;
+    for(;;) {
+        auto gnr = ::GetNext(listJob);
+
+        if (gnr.r0 == ERROR_AND_STOP_CALLING) {
+            errorOut.append(QString(gnr.r1.p)); // log error
+            break; // done
+
+        } else if (gnr.r0 == ERROR_AND_KEEP_CALLING) {
+            errorOut.append(QString(gnr.r1.p)); // log error
+            continue;
+
+        } else if (gnr.r0 == FINISHED_OK) {
+            // Once we hit this, the go-side will clean up the channel / associated goroutines
+            break;
+
+        } else if (gnr.r0 == REAL_MESSAGE) {
+            cb(QByteArray(gnr.r1.p, gnr.r1.n));
+            continue;
+        }
     }
 
-    return true;
+    return (errorOut.length() == 0);
 }
 
 BoltDB::~BoltDB()