From 14cb587b7e4230830ca0b520dcd0eb9c723b1041 Mon Sep 17 00:00:00 2001
From: Sam <sam.saffron@gmail.com>
Date: Fri, 16 Oct 2020 10:51:58 +1100
Subject: [PATCH] PERF: don't ask for new posts while loading new posts
 (#10937)

Previous to this change we had no protection to ensure we wait on a request
for more posts prior starting another request.

In outlier cases if 10 people post at the same time on a topic a flood of
requests could start.

To improve this situation we now ensure that we are done asking for new posts
prior to asking for the next batch.

Also addresses some style issues raised previously and moves init to top
of class.
---
 .../discourse/app/controllers/topic.js        | 114 ++++++++++--------
 1 file changed, 66 insertions(+), 48 deletions(-)

diff --git a/app/assets/javascripts/discourse/app/controllers/topic.js b/app/assets/javascripts/discourse/app/controllers/topic.js
index c7b91cdf238..8937823e4e5 100644
--- a/app/assets/javascripts/discourse/app/controllers/topic.js
+++ b/app/assets/javascripts/discourse/app/controllers/topic.js
@@ -68,6 +68,31 @@ export default Controller.extend(bufferedProperty("model"), {
   filter: null,
   quoteState: null,
 
+  init() {
+    this._super(...arguments);
+
+    this._retryInProgress = false;
+    this._retryRateLimited = false;
+    this._newPostsInStream = [];
+
+    this.appEvents.on("post:show-revision", this, "_showRevision");
+    this.appEvents.on("post:created", this, () => {
+      this._removeDeleteOnOwnerReplyBookmarks();
+      this.appEvents.trigger("post-stream:refresh", { force: true });
+    });
+
+    this.setProperties({
+      selectedPostIds: [],
+      quoteState: new QuoteState(),
+    });
+  },
+
+  willDestroy() {
+    this._super(...arguments);
+
+    this.appEvents.off("post:show-revision", this, "_showRevision");
+  },
+
   canRemoveTopicFeaturedLink: and(
     "canEditTopicFeaturedLink",
     "buffered.featured_link"
@@ -115,27 +140,6 @@ export default Controller.extend(bufferedProperty("model"), {
     return this.currentUser && this.currentUser.pmPath(topic);
   },
 
-  init() {
-    this._super(...arguments);
-
-    this.appEvents.on("post:show-revision", this, "_showRevision");
-    this.appEvents.on("post:created", this, () => {
-      this._removeDeleteOnOwnerReplyBookmarks();
-      this.appEvents.trigger("post-stream:refresh", { force: true });
-    });
-
-    this.setProperties({
-      selectedPostIds: [],
-      quoteState: new QuoteState(),
-    });
-  },
-
-  willDestroy() {
-    this._super(...arguments);
-
-    this.appEvents.off("post:show-revision", this, "_showRevision");
-  },
-
   _showRevision(postNumber, revision) {
     const post = this.model.get("postStream").postForPostNumber(postNumber);
     if (!post) {
@@ -1302,32 +1306,45 @@ export default Controller.extend(bufferedProperty("model"), {
       return;
     }
 
-    if (this.retryRateLimited || times <= 0) {
+    if (this._retryRateLimited || times <= 0) {
       return;
     }
 
-    promise().catch((e) => {
-      const xhr = e.jqXHR;
-      if (
-        xhr &&
-        xhr.status === 429 &&
-        xhr.responseJSON &&
-        xhr.responseJSON.extras &&
-        xhr.responseJSON.extras.wait_seconds
-      ) {
-        let waitSeconds = xhr.responseJSON.extras.wait_seconds;
-        if (waitSeconds < 5) {
-          waitSeconds = 5;
+    if (this._retryInProgress) {
+      later(() => {
+        this.retryOnRateLimit(times, promise, topicId);
+      }, 100);
+      return;
+    }
+
+    this._retryInProgress = true;
+
+    promise()
+      .catch((e) => {
+        const xhr = e.jqXHR;
+        if (
+          xhr &&
+          xhr.status === 429 &&
+          xhr.responseJSON &&
+          xhr.responseJSON.extras &&
+          xhr.responseJSON.extras.wait_seconds
+        ) {
+          let waitSeconds = xhr.responseJSON.extras.wait_seconds;
+          if (waitSeconds < 5) {
+            waitSeconds = 5;
+          }
+
+          this._retryRateLimited = true;
+
+          later(() => {
+            this._retryRateLimited = false;
+            this.retryOnRateLimit(times - 1, promise, topicId);
+          }, waitSeconds * 1000);
         }
-
-        this.retryRateLimited = true;
-
-        later(() => {
-          this.retryRateLimited = false;
-          this.retryOnRateLimit(times - 1, promise, topicId);
-        }, waitSeconds * 1000);
-      }
-    });
+      })
+      .finally(() => {
+        this._retryInProgress = false;
+      });
   },
 
   subscribe() {
@@ -1401,18 +1418,19 @@ export default Controller.extend(bufferedProperty("model"), {
             break;
           }
           case "created": {
-            this.newPostsInStream = this.newPostsInStream || [];
-            this.newPostsInStream.push(data.id);
+            this._newPostsInStream.push(data.id);
 
             this.retryOnRateLimit(RETRIES_ON_RATE_LIMIT, () => {
-              const postIds = this.newPostsInStream;
-              this.newPostsInStream = [];
+              const postIds = this._newPostsInStream;
+              this._newPostsInStream = [];
 
               return postStream
                 .triggerNewPostsInStream(postIds, { background: true })
                 .then(() => refresh())
                 .catch((e) => {
-                  this.newPostsInStream = postIds.concat(this.newPostsInStream);
+                  this._newPostsInStream = postIds.concat(
+                    this._newPostsInStream
+                  );
                   throw e;
                 });
             });