gstUtils: creates a GObject wrapper for GstPromise

Since the reference management of boxed object in Node-GTK is somewhat
broken, I've decided to use GObject as a vehicle instead. This also
allow thread trampolining to happen in C instead of JS.

src-native/NgwNativePromise.c

@@ -0,0 +1,89 @@
+#include "NgwNativePromise.h"
+
+struct _NgwNativePromise
+{
+  GObject parent_instance;
+
+  GstPromise * gst_promise;
+};
+
+G_DEFINE_TYPE(NgwNativePromise, ngw_native_promise, G_TYPE_OBJECT)
+
+enum {
+  SIGNAL_ON_CHANGED,
+  LAST_SIGNAL,
+};
+
+static guint promise_signals[LAST_SIGNAL] = { 0 };
+
+static void ngw_native_promise_dispose (GObject *);
+
+static void
+ngw_native_promise_class_init(NgwNativePromiseClass * klass)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (klass);
+
+  object_class->dispose = ngw_native_promise_dispose;
+
+  /**
+   * NgwNativePromise::on-changed:
+   * @object: the #NgwNativePromise
+   */
+  promise_signals[SIGNAL_ON_CHANGED] =
+      g_signal_new ("on-changed", G_TYPE_FROM_CLASS (klass),
+      G_SIGNAL_RUN_LAST, 0, NULL, NULL, NULL, G_TYPE_NONE, 0);
+}
+
+static void on_gst_promise_changed (GstPromise * promise, gpointer user_data);
+
+static void
+ngw_native_promise_init (NgwNativePromise * self)
+{
+  // XXX: will have to make sure JS side hold this object long enough.
+  self->gst_promise = gst_promise_new_with_change_func(
+    on_gst_promise_changed, /* user_data */ self, /* GDestroyNotify */ NULL);
+}
+
+static gboolean
+handle_gst_promise_changed_on_idle (gpointer user_data)
+{
+  NgwNativePromise * self = NGW_NATIVE_PROMISE(user_data);
+
+  g_signal_emit(self, promise_signals[SIGNAL_ON_CHANGED], /* detail */ 0);
+
+  return G_SOURCE_REMOVE;
+}
+
+static void
+on_gst_promise_changed (GstPromise * promise G_GNUC_UNUSED, gpointer user_data)
+{
+  NgwNativePromise * self = NGW_NATIVE_PROMISE(user_data);
+
+  g_idle_add (handle_gst_promise_changed_on_idle, self);
+}
+
+/**
+ * ngw_native_promise_get_gst_promise:
+ * @self: the #NgwNativePromise
+ *
+ * Returns: (transfer none): the #GstPromise
+ */
+GstPromise *
+ngw_native_promise_get_gst_promise (NgwNativePromise * self)
+{
+  return self->gst_promise;
+}
+
+static void
+ngw_native_promise_dispose (GObject * gobject)
+{
+  NgwNativePromise * self = NGW_NATIVE_PROMISE(gobject);
+
+  g_clear_pointer(&self->gst_promise, gst_promise_unref);
+}
+
+NgwNativePromise *
+ngw_native_promise_new (void)
+{
+  return g_object_new (NGW_NATIVE_PROMISE_TYPE, NULL);
+}

src-native/NgwNativePromise.h

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <glib-object.h>
+#include <gst/gstpromise.h>
+
+#include "NgwNativeCommon.h"
+
+G_BEGIN_DECLS
+
+#define NGW_NATIVE_PROMISE_TYPE ngw_native_promise_get_type()
+NGWNATIVE_PUBLIC G_DECLARE_FINAL_TYPE(
+  NgwNativePromise,
+  ngw_native_promise,
+  NGW_NATIVE, PROMISE, GObject)
+
+NGWNATIVE_PUBLIC
+NgwNativePromise * ngw_native_promise_new(void);
+
+NGWNATIVE_PUBLIC
+GstPromise * ngw_native_promise_get_gst_promise(NgwNativePromise * self);
+
+G_END_DECLS

src-native/meson.build

@@ -7,10 +7,12 @@ project('NgwNative', 'c',
 lib_args = ['-DBUILDING_NGWNATIVE']
 
 src_files = [
+  'NgwNativePromise.c',
   'NgwNativeRTCDataChannel.c'
 ]
 
 header_files = [
+  'NgwNativePromise.h',
   'NgwNativeRTCDataChannel.h'
 ]
 

src/@types/node-ngwnative-0.0.d.ts

@@ -21,6 +21,72 @@ import type GModule from './node-gmodule-2.0.js';
 
 export namespace NgwNative {
 
+module Promise {
+
+    // Signal callback interfaces
+
+    /**
+     * Signal callback interface for `on-changed`
+     */
+    interface OnChangedSignalCallback {
+        (): void
+    }
+
+
+    // Constructor properties interface
+
+    interface ConstructorProperties extends GObject.Object.ConstructorProperties {
+    }
+
+}
+
+interface Promise {
+
+    // Own properties of NgwNative-0.0.NgwNative.Promise
+
+    __gtype__: number
+
+    // Owm methods of NgwNative-0.0.NgwNative.Promise
+
+    getGstPromise(): Gst.Promise
+
+    // Own signals of NgwNative-0.0.NgwNative.Promise
+
+    connect(sigName: "on-changed", callback: Promise.OnChangedSignalCallback): number
+    on(sigName: "on-changed", callback: Promise.OnChangedSignalCallback, after?: boolean): NodeJS.EventEmitter
+    once(sigName: "on-changed", callback: Promise.OnChangedSignalCallback, after?: boolean): NodeJS.EventEmitter
+    off(sigName: "on-changed", callback: Promise.OnChangedSignalCallback): NodeJS.EventEmitter
+    emit(sigName: "on-changed", ...args: any[]): void
+
+    // Class property signals of NgwNative-0.0.NgwNative.Promise
+
+    connect(sigName: "notify::__gtype__", callback: (...args: any[]) => void): number
+    on(sigName: "notify::__gtype__", callback: (...args: any[]) => void, after?: boolean): NodeJS.EventEmitter
+    once(sigName: "notify::__gtype__", callback: (...args: any[]) => void, after?: boolean): NodeJS.EventEmitter
+    off(sigName: "notify::__gtype__", callback: (...args: any[]) => void): NodeJS.EventEmitter
+    emit(sigName: "notify::__gtype__", ...args: any[]): void
+    connect(sigName: string, callback: (...args: any[]) => void): number
+    on(sigName: string, callback: (...args: any[]) => void, after?: boolean): NodeJS.EventEmitter
+    once(sigName: string, callback: (...args: any[]) => void, after?: boolean): NodeJS.EventEmitter
+    off(sigName: string, callback: (...args: any[]) => void): NodeJS.EventEmitter
+    emit(sigName: string, ...args: any[]): void
+    disconnect(id: number): void
+}
+
+class Promise extends GObject.Object {
+
+    // Own properties of NgwNative-0.0.NgwNative.Promise
+
+    static name: string
+
+    // Constructors of NgwNative-0.0.NgwNative.Promise
+
+    constructor(config?: Promise.ConstructorProperties) 
+    constructor() 
+    static new(): Promise
+    _init(config?: Promise.ConstructorProperties): void
+}
+
 module RTCDataChannel {
 
     // Signal callback interfaces
@@ -153,6 +219,20 @@ class RTCDataChannel extends GObject.Object {
     _init(config?: RTCDataChannel.ConstructorProperties): void
 }
 
+interface PromiseClass {
+
+    // Own fields of NgwNative-0.0.NgwNative.PromiseClass
+
+    parentClass: GObject.ObjectClass
+}
+
+abstract class PromiseClass {
+
+    // Own properties of NgwNative-0.0.NgwNative.PromiseClass
+
+    static name: string
+}
+
 interface RTCDataChannelClass {
 
     // Own fields of NgwNative-0.0.NgwNative.RTCDataChannelClass

src/gstUtils.ts

@@ -1,4 +1,4 @@
-import { setImmediate as resolveImmediate } from 'timers/promises';
+import NgwNative from './@types/node-ngwnative-0.0';
 
 // For convenience
 import GLib from './@types/node-glib-2.0';
@@ -16,45 +16,35 @@ Gst.init(null);
 // UINT64_MAX.
 export const GST_CLOCK_TIME_NONE = BigInt.asUintN(/* width */ 64, -1n);
 
-async function rejectImmediate(reason: any): Promise<any> {
-  await resolveImmediate();
-  throw reason;
-}
-
-// Node-gtk doesn't handle circular reference well, and GstPromise doesn't have
-// a way to change the changeFunc, so we have to create a change function that
-// doesn't capture the GstPromise itself in a closure to prevent circular reference.
-function getGstPromiseChangeFuncForResolveReject(
-  resolve: (s: Promise<Gst.Structure | null>) => void,
-  reject: (reason: any) => void,
-) {
-  return function changeFunc (gstPromise: Gst.Promise) {
-    switch (gstPromise.wait()) {
-      case Gst.PromiseResult.EXPIRED:
-        resolve(rejectImmediate(new Error('GstPromise is expired.')));
-        break;
-      case Gst.PromiseResult.INTERRUPTED:
-        resolve(rejectImmediate(new Error('GstPromise is interrupted.')));
-        break;
-      case Gst.PromiseResult.REPLIED:
-        let reply = gstPromise.getReply();
-        if (reply && reply.hasField('error')) {
-          let errorV = <GObject.Value>reply.getValue('error');
-          let error = <GLib.Error>errorV.getBoxed();
-          errorV.unset();
-
-          resolve(rejectImmediate(new Error(error.message || undefined)));
-        } else {
-          resolve(resolveImmediate(reply));
-        }
-    }
-  }
-}
-
 export function withGstPromise(f: (p: Gst.Promise) => void) {
   return new Promise<Gst.Structure | null>((resolve, reject) => {
-    const gstPromise = Gst.Promise.newWithChangeFunc(
-      getGstPromiseChangeFuncForResolveReject(resolve, reject));
-    f(gstPromise);
+    let gstPromiseWrapper = new NgwNative.Promise();
+
+    gstPromiseWrapper.once("on-changed", () => {
+      // Pull gstPromiseWrapper itself into the closure.
+      let gstPromise = gstPromiseWrapper.getGstPromise();
+
+      switch (gstPromise.wait()) {
+        case Gst.PromiseResult.EXPIRED:
+          reject(new Error('GstPromise is expired.'));
+          break;
+        case Gst.PromiseResult.INTERRUPTED:
+          reject(new Error('GstPromise is interrupted.'));
+          break;
+        case Gst.PromiseResult.REPLIED:
+          let reply = gstPromise.getReply();
+          if (reply && reply.hasField('error')) {
+            let errorV = <GObject.Value>reply.getValue('error');
+            let error = <GLib.Error>errorV.getBoxed();
+            errorV.unset();
+
+            reject(new Error(error.message || undefined));
+          } else {
+            resolve(reply);
+          }
+      }
+    });
+
+    f(gstPromiseWrapper.getGstPromise());
   });
 }