Do library checks from up to 5 sources concurrently

app/src/main/java/eu/kanade/tachiyomi/data/library/LibraryUpdateService.kt

@@ -308,9 +308,13 @@ class LibraryUpdateService(
 
         // Emit each manga and update it sequentially.
         return Observable.from(mangaToUpdate)
+            // Update the chapters of the manga concurrently from 5 different sources
+            .groupBy { it.source }
+            .flatMap(
+                { bySource ->
+                    bySource
                         // Notify manga that will update.
                         .doOnNext { showProgressNotification(it, count.andIncrement, mangaToUpdate.size) }
-            // Update the chapters of the manga.
                         .concatMap { manga ->
                             updateManga(manga)
                                 // If there's any error, return empty update and continue.
@@ -334,10 +338,16 @@ class LibraryUpdateService(
                                 .map {
                                     Pair(
                                         manga,
-                            (it.first.sortedByDescending { ch -> ch.source_order }.toTypedArray())
+                                        (
+                                            it.first.sortedByDescending { ch -> ch.source_order }
+                                                .toTypedArray()
+                                            )
                                     )
                                 }
                         }
+                },
+                5
+            )
             // Add manga with new chapters to the list.
             .doOnNext { manga ->
                 // Add to the list
@@ -397,9 +407,13 @@ class LibraryUpdateService(
 
         // Emit each manga and update it sequentially.
         return Observable.from(mangaToUpdate)
+            // Update the details of the manga concurrently from 5 different sources
+            .groupBy { it.source }
+            .flatMap(
+                { bySource ->
+                    bySource
                         // Notify manga that will update.
                         .doOnNext { showProgressNotification(it, count.andIncrement, mangaToUpdate.size) }
-            // Update the details of the manga.
                         .concatMap { manga ->
                             val source = sourceManager.get(manga.source) as? HttpSource
                                 ?: return@concatMap Observable.empty<LibraryManga>()
@@ -412,6 +426,9 @@ class LibraryUpdateService(
                                 }
                                 .onErrorReturn { manga }
                         }
+                },
+                5
+            )
             .doOnCompleted {
                 cancelProgressNotification()
             }