From 3cc7de2f7a460333edcba9135e741da025896ce5 Mon Sep 17 00:00:00 2001
From: ikiw <sakthivel.elango@linkedin.com>
Date: Tue, 18 Feb 2020 18:38:13 +0530
Subject: [PATCH] 1.Resolve #7889 to fetch only 1 checkpoint call per notebook.
 2.Refactor PR 7879 to use debouncer

---
 packages/docmanager-extension/src/index.ts | 14 +++---
 packages/services/src/contents/index.ts    | 52 +++++++++++++++-------
 2 files changed, 42 insertions(+), 24 deletions(-)

diff --git a/packages/docmanager-extension/src/index.ts b/packages/docmanager-extension/src/index.ts
index a73280981442..5e9a02d59127 100644
--- a/packages/docmanager-extension/src/index.ts
+++ b/packages/docmanager-extension/src/index.ts
@@ -44,6 +44,8 @@ import { IDisposable } from '@lumino/disposable';
 
 import { Widget } from '@lumino/widgets';
 
+import { Debouncer } from '@lumino/polling';
+
 /**
  * The command IDs used by the document manager plugin.
  */
@@ -244,15 +246,11 @@ ${fileTypes}`;
 
     // callback to registry change that ensures not to invoke reload method when there is already a promise that is pending
     let reloadSettingsRegistry = () => {
-      let promisePending = false;
+      let reloadDebounce = new Debouncer(() =>
+        settingRegistry.reload(pluginId)
+      );
 
-      return async () => {
-        if (!promisePending) {
-          promisePending = true;
-          await settingRegistry.reload(pluginId);
-          promisePending = false;
-        }
-      };
+      return reloadDebounce.invoke.bind(reloadDebounce);
     };
 
     // If the document registry gains or loses a factory or file type,
diff --git a/packages/services/src/contents/index.ts b/packages/services/src/contents/index.ts
index 0377aa57fa86..4611252dbbd9 100644
--- a/packages/services/src/contents/index.ts
+++ b/packages/services/src/contents/index.ts
@@ -27,6 +27,14 @@ const SERVICE_DRIVE_URL = 'api/contents';
  */
 const FILES_URL = 'files';
 
+/**
+ * The object to reference listCheckpoints promises
+ * used as a flag to check and return the existing promise if it's pending
+ */
+let checkpointPromiseQueue: {
+  [key: string]: Promise<Contents.ICheckpointModel[]>;
+} = {};
+
 /**
  * A namespace for contents interfaces.
  */
@@ -1309,22 +1317,34 @@ export class Drive implements Contents.IDrive {
    */
   listCheckpoints(localPath: string): Promise<Contents.ICheckpointModel[]> {
     let url = this._getUrl(localPath, 'checkpoints');
-    return ServerConnection.makeRequest(url, {}, this.serverSettings)
-      .then(response => {
-        if (response.status !== 200) {
-          throw new ServerConnection.ResponseError(response);
-        }
-        return response.json();
-      })
-      .then(data => {
-        if (!Array.isArray(data)) {
-          throw new Error('Invalid Checkpoint list');
-        }
-        for (let i = 0; i < data.length; i++) {
-          validate.validateCheckpointModel(data[i]);
-        }
-        return data;
-      });
+
+    if (!checkpointPromiseQueue[localPath]) {
+      checkpointPromiseQueue[localPath] = ServerConnection.makeRequest(
+        url,
+        {},
+        this.serverSettings
+      )
+        .then(response => {
+          if (response.status !== 200) {
+            throw new ServerConnection.ResponseError(response);
+          }
+          return response.json();
+        })
+        .then(data => {
+          if (!Array.isArray(data)) {
+            throw new Error('Invalid Checkpoint list');
+          }
+          for (let i = 0; i < data.length; i++) {
+            validate.validateCheckpointModel(data[i]);
+          }
+          return data;
+        })
+        .finally(() => {
+          delete checkpointPromiseQueue[localPath];
+        });
+    }
+
+    return checkpointPromiseQueue[localPath];
   }
 
   /**