Add option to customize concurrent downloads, increase page concurrency (mihonapp/mihon#2637)

(cherry picked from commit 643762f91325a460c74398d472a555fb00ed9f63)

app/src/main/java/eu/kanade/presentation/more/settings/screen/SettingsDownloadScreen.kt

@@ -39,6 +39,8 @@ object SettingsDownloadScreen : SearchableSettings {
         val allCategories by getCategories.subscribe().collectAsState(initial = emptyList())
 
         val downloadPreferences = remember { Injekt.get<DownloadPreferences>() }
+        val parallelSourceLimit by downloadPreferences.parallelSourceLimit().collectAsState()
+        val parallelPageLimit by downloadPreferences.parallelPageLimit().collectAsState()
         return listOf(
             Preference.PreferenceItem.SwitchPreference(
                 preference = downloadPreferences.downloadOnlyOverWifi(),
@@ -53,6 +55,19 @@ object SettingsDownloadScreen : SearchableSettings {
                 title = stringResource(MR.strings.split_tall_images),
                 subtitle = stringResource(MR.strings.split_tall_images_summary),
             ),
+            Preference.PreferenceItem.SliderPreference(
+                value = parallelSourceLimit,
+                valueRange = 1..10,
+                title = stringResource(MR.strings.pref_download_concurrent_sources),
+                onValueChanged = { downloadPreferences.parallelSourceLimit().set(it) },
+            ),
+            Preference.PreferenceItem.SliderPreference(
+                value = parallelPageLimit,
+                valueRange = 1..15,
+                title = stringResource(MR.strings.pref_download_concurrent_pages),
+                subtitle = stringResource(MR.strings.pref_download_concurrent_pages_summary),
+                onValueChanged = { downloadPreferences.parallelPageLimit().set(it) },
+            ),
             getDeleteChaptersGroup(
                 downloadPreferences = downloadPreferences,
                 categories = allCategories,

app/src/main/java/eu/kanade/tachiyomi/data/download/Downloader.kt

@@ -202,15 +202,17 @@ class Downloader(
         if (isRunning) return
 
         downloaderJob = scope.launch {
-            val activeDownloadsFlow = queueState.transformLatest { queue ->
+            val activeDownloadsFlow = combine(
+                queueState,
+                downloadPreferences.parallelSourceLimit().changes(),
+            ) { a, b -> a to b }.transformLatest { (queue, parallelCount) ->
                 while (true) {
                     val activeDownloads = queue.asSequence()
                         // Ignore completed downloads, leave them in the queue
                         .filter { it.status.value <= Download.State.DOWNLOADING.value }
                         .groupBy { it.source }
                         .toList()
-                        // Concurrently download from 5 different sources
+                        .take(parallelCount)
-                        .take(5)
                         .map { (_, downloads) -> downloads.first() }
                     emit(activeDownloads)
 
@@ -222,7 +224,8 @@ class Downloader(
                         }.filter { it }
                     activeDownloadsErroredFlow.first()
                 }
-            }.distinctUntilChanged()
+            }
+                .distinctUntilChanged()
 
             // Use supervisorScope to cancel child jobs when the downloader job is cancelled
             supervisorScope {
@@ -390,24 +393,23 @@ class Downloader(
             download.status = Download.State.DOWNLOADING
 
             // Start downloading images, consider we can have downloaded images already
-            // Concurrently do 2 pages at a time
+            pageList.asFlow().flatMapMerge(concurrency = downloadPreferences.parallelPageLimit().get()) { page ->
-            pageList.asFlow()
+                flow {
-                .flatMapMerge(concurrency = 2) { page ->
+                    // Fetch image URL if necessary
-                    flow {
+                    if (page.imageUrl.isNullOrEmpty()) {
-                        // Fetch image URL if necessary
+                        page.status = Page.State.LoadPage
-                        if (page.imageUrl.isNullOrEmpty()) {
+                        try {
-                            page.status = Page.State.LoadPage
+                            page.imageUrl = download.source.getImageUrl(page)
-                            try {
+                        } catch (e: Throwable) {
-                                page.imageUrl = download.source.getImageUrl(page)
+                            page.status = Page.State.Error(e)
-                            } catch (e: Throwable) {
-                                page.status = Page.State.Error(e)
-                            }
                         }
+                    }
 
-                        withIOContext { getOrDownloadImage(page, download, tmpDir, dataSaver) }
+                    withIOContext { getOrDownloadImage(page, download, tmpDir, dataSaver) }
-                        emit(page)
+                    emit(page)
-                    }.flowOn(Dispatchers.IO)
                 }
+                    .flowOn(Dispatchers.IO)
+            }
                 .collect {
                     // Do when page is downloaded.
                     notifier.onProgressChange(download)

domain/src/main/java/tachiyomi/domain/download/service/DownloadPreferences.kt

@@ -37,6 +37,10 @@ class DownloadPreferences(
 
     fun downloadNewUnreadChaptersOnly() = preferenceStore.getBoolean("download_new_unread_chapters_only", false)
 
+    fun parallelSourceLimit() = preferenceStore.getInt("download_parallel_source_limit", 5)
+
+    fun parallelPageLimit() = preferenceStore.getInt("download_parallel_page_limit", 5)
+
     // KMK -->
     fun downloadCacheRenewInterval() = preferenceStore.getInt("download_cache_renew_interval", 1)
     // KMK <--

i18n/src/commonMain/moko-resources/base/strings.xml

@@ -522,6 +522,9 @@
     <string name="save_chapter_as_cbz">Save as CBZ archive</string>
     <string name="split_tall_images">Split tall images</string>
     <string name="split_tall_images_summary">Improves reader performance</string>
+    <string name="pref_download_concurrent_sources">Concurrent source downloads</string>
+    <string name="pref_download_concurrent_pages">Concurrent page downloads</string>
+    <string name="pref_download_concurrent_pages_summary">Pages downloaded simultaneously per source</string>
 
     <!-- Tracking section -->
     <string name="tracking_guide">Tracking guide</string>