From ba43eeafaa2de878136f78d019c3c1fb49fd4545 Mon Sep 17 00:00:00 2001
From: "Maarten A. Breddels" <maartenbreddels@gmail.com>
Date: Wed, 23 Mar 2022 10:14:53 +0100
Subject: [PATCH] fix: avoid using a global force_load widget

---
 ipyvue/ForceLoad.py         |  3 ---
 ipyvue/VueTemplateWidget.py | 14 +++++++++-----
 ipyvue/VueWidget.py         | 19 ++++++++++++++-----
 ipyvue/util.py              | 24 ++++++++++++++++++++++++
 4 files changed, 47 insertions(+), 13 deletions(-)
 create mode 100644 ipyvue/util.py

diff --git a/ipyvue/ForceLoad.py b/ipyvue/ForceLoad.py
index 1cc797a..9249013 100644
--- a/ipyvue/ForceLoad.py
+++ b/ipyvue/ForceLoad.py
@@ -7,6 +7,3 @@ class ForceLoad(DOMWidget):
     _model_name = Unicode("ForceLoadModel").tag(sync=True)
     _model_module = Unicode("jupyter-vue").tag(sync=True)
     _model_module_version = Unicode(semver).tag(sync=True)
-
-
-force_load_instance = ForceLoad()
diff --git a/ipyvue/VueTemplateWidget.py b/ipyvue/VueTemplateWidget.py
index 54b00c2..38d270e 100644
--- a/ipyvue/VueTemplateWidget.py
+++ b/ipyvue/VueTemplateWidget.py
@@ -1,11 +1,12 @@
 import os
-from traitlets import Any, Unicode, List, Dict, Union, Instance
+from traitlets import Any, Unicode, List, Dict, Union, Instance, default
 from ipywidgets import DOMWidget
 from ipywidgets.widgets.widget import widget_serialization
 
 from .Template import Template, get_template
 from ._version import semver
-from .ForceLoad import force_load_instance
+from .ForceLoad import ForceLoad
+from .util import singleton
 import inspect
 from importlib import import_module
 
@@ -94,12 +95,15 @@ class VueTemplate(DOMWidget, Events):
         "to_json": _class_to_json,
     }
 
-    # Force the loading of jupyter-vue before dependent extensions when in a static
-    # context (embed, voila)
-    _jupyter_vue = Any(force_load_instance, read_only=True).tag(
+    # see VueWidget
+    _jupyter_vue = Instance(ForceLoad, read_only=True).tag(
         sync=True, **widget_serialization
     )
 
+    @default("_jupyter_vue")
+    def _default_jupyter_vue(self):
+        return singleton(ForceLoad)
+
     _model_name = Unicode("VueTemplateModel").tag(sync=True)
 
     _view_name = Unicode("VueView").tag(sync=True)
diff --git a/ipyvue/VueWidget.py b/ipyvue/VueWidget.py
index b85a737..5421733 100644
--- a/ipyvue/VueWidget.py
+++ b/ipyvue/VueWidget.py
@@ -1,11 +1,12 @@
-from traitlets import Unicode, Instance, Union, List, Any, Dict
 from ipywidgets import DOMWidget
-from ipywidgets.widgets.widget_layout import Layout
-from ipywidgets.widgets.widget import widget_serialization, CallbackDispatcher
 from ipywidgets.widgets.trait_types import InstanceDict
+from ipywidgets.widgets.widget import CallbackDispatcher, widget_serialization
+from ipywidgets.widgets.widget_layout import Layout
+from traitlets import Any, Dict, Instance, List, Unicode, Union, default
 
 from ._version import semver
-from .ForceLoad import force_load_instance
+from .ForceLoad import ForceLoad
+from .util import singleton
 
 
 class ClassList:
@@ -138,10 +139,18 @@ class VueWidget(DOMWidget, Events):
 
     # Force the loading of jupyter-vue before dependent extensions when in a static
     # context (embed, voila)
-    _jupyter_vue = Any(force_load_instance, read_only=True).tag(
+    # this happens when e.g. jupyter-vuedraggable requires jupyter-vue, but it is not
+    # loaded yet (via a widget creation). This does not trigger the library loading
+    # via the widget manager, but straight through requirejs
+
+    _jupyter_vue = Instance(ForceLoad, read_only=True).tag(
         sync=True, **widget_serialization
     )
 
+    @default("_jupyter_vue")
+    def _default_jupyter_vue(self):
+        return singleton(ForceLoad)
+
     _model_name = Unicode("VueModel").tag(sync=True)
 
     _view_name = Unicode("VueView").tag(sync=True)
diff --git a/ipyvue/util.py b/ipyvue/util.py
new file mode 100644
index 0000000..34655c4
--- /dev/null
+++ b/ipyvue/util.py
@@ -0,0 +1,24 @@
+from ipywidgets import Widget
+import threading
+
+
+lock = threading.Lock()
+
+
+def singleton(WidgetClass, **kwargs):
+    # find a 'shared' instance (singleton) to avoid creating
+    # too many widgets. In contexts where self.widgets is not
+    # a global dict, this allows different users/context to
+    # have a singleton without sharing the widget
+    with lock:
+        if hasattr(Widget, "widgets"):
+            # pre 8.0
+            all_widgets = Widget.widgets
+        if hasattr(Widget, "widgets"):
+            all_widgets = Widget._widgets
+        else:
+
+        for widget in all_widgets.values():
+            if isinstance(widget, WidgetClass):
+                return widget
+        return WidgetClass(**kwargs)