Bug 1974237 - part2 : use nsTHashSet to perform O(1) search in order to improve the performance. r=media-playback-reviewers,padenot

In a test scenario with approximately 40000 cues, the speed improvement is
dropping from around 200ms to about 5ms.

Differential Revision: https://phabricator.services.mozilla.com/D256513

Author: alastor0325

dom/media/webvtt/TextTrackCueList.cpp

@@ -68,14 +68,15 @@ TextTrackCue* TextTrackCueList::GetCueById(const nsAString& aId) {
 }
 
 void TextTrackCueList::AddCue(TextTrackCue& aCue) {
-  if (mList.Contains(&aCue)) {
+  if (mCueSet.Contains(&aCue)) {
     return;
   }
   mList.InsertElementSorted(&aCue, CompareCuesByTime());
+  mCueSet.Insert(&aCue);
 }
 
 void TextTrackCueList::RemoveCue(TextTrackCue& aCue, ErrorResult& aRv) {
-  if (!mList.Contains(&aCue)) {
+  if (!mCueSet.Contains(&aCue)) {
     aRv.Throw(NS_ERROR_DOM_NOT_FOUND_ERR);
     return;
   }
@@ -84,6 +85,7 @@ void TextTrackCueList::RemoveCue(TextTrackCue& aCue, ErrorResult& aRv) {
 
 void TextTrackCueList::RemoveCue(TextTrackCue& aCue) {
   mList.RemoveElement(&aCue);
+  mCueSet.Remove(&aCue);
 }
 
 void TextTrackCueList::GetArray(nsTArray<RefPtr<TextTrackCue>>& aCues) {
@@ -104,7 +106,7 @@ void TextTrackCueList::NotifyCueUpdated(TextTrackCue* aCue) {
 }
 
 bool TextTrackCueList::IsCueExist(TextTrackCue* aCue) {
-  if (aCue && mList.Contains(aCue)) {
+  if (aCue && mCueSet.Contains(aCue)) {
     return true;
   }
   return false;

dom/media/webvtt/TextTrackCueList.h

@@ -10,6 +10,7 @@
 #include "nsTArray.h"
 #include "nsCOMPtr.h"
 #include "nsCycleCollectionParticipant.h"
+#include "nsTHashSet.h"
 #include "nsWrapperCache.h"
 
 namespace mozilla {
@@ -64,6 +65,9 @@ class TextTrackCueList final : public nsISupports, public nsWrapperCache {
   // A sorted list of TextTrackCues sorted by earliest start time. If the start
   // times are equal then it will be sorted by end time, earliest first.
   nsTArray<RefPtr<TextTrackCue>> mList;
+
+  // Utilized for rapid cue existence verification.
+  nsTHashSet<TextTrackCue*> mCueSet;
 };
 
 }  // namespace dom