Added delays for getWidgetManager and get_model if the model isn't im…

…mediately available.

packages/base-manager/src/manager-base.ts

@@ -215,9 +215,13 @@ export abstract class ManagerBase implements IWidgetManager {
    * If you would like to synchronously test if a model exists, use .has_model().
    */
   async get_model(model_id: string): Promise<WidgetModel> {
+    let i = 0;
+    while (!this._models[model_id] && i < this._sleepTimes.length) {
+      new Promise((r) => setTimeout(r, this._sleepTimes[i++]))
+    }
     const modelPromise = this._models[model_id];
     if (modelPromise === undefined) {
-      throw new Error('widget model not found');
+      throw new Error(`widget model '${model_id}' not found`);
     }
     return modelPromise;
   }
@@ -874,6 +878,7 @@ export abstract class ManagerBase implements IWidgetManager {
   /**
    * Dictionary of model ids and model instance promises
    */
+  private _sleepTimes = [2, 50, 200, 800];
   private _models: { [key: string]: Promise<WidgetModel> } =
     Object.create(null);
 }

python/jupyterlab_widgets/src/manager.ts

@@ -802,10 +802,15 @@ function configureRendermime(
 /**
  * Get the widgetManager that owns the model.
  */
-export function getWidgetManager(model_id: string): KernelWidgetManager | null {
-  for (const wManager of Private.kernelWidgetManagers.values()) {
-    if (wManager.has_model(model_id)) {
-      return wManager;
+export async function getWidgetManager(
+  model_id: string
+): Promise<KernelWidgetManager | null> {
+  for (const sleepTime of [0, 50, 1000]) {
+    await new Promise((r) => setTimeout(r, sleepTime));
+    for (const wManager of Private.kernelWidgetManagers.values()) {
+      if (wManager.has_model(model_id)) {
+        return wManager;
+      }
     }
   }
   return null;

python/jupyterlab_widgets/src/renderer.ts

@@ -73,7 +73,7 @@ export class WidgetRenderer
       return Promise.resolve();
     }
     if (!this._pendingManagerMessage && !this._managerIsSet) {
-      this.manager = getWidgetManager(source.model_id);
+      this.manager = await getWidgetManager(source.model_id);
     }
     this.node.textContent = `${
       this._pendingManagerMessage || model.data['text/plain']