music: fix threading problems

Fix issues with the current threading approach with the new parallel
music loader.

app/src/main/java/org/oxycblt/auxio/music/extractor/MediaStoreExtractor.kt

@@ -28,6 +28,7 @@ import androidx.core.database.getIntOrNull
 import androidx.core.database.getStringOrNull
 import java.io.File
 import kotlinx.coroutines.channels.Channel
+import kotlinx.coroutines.yield
 import org.oxycblt.auxio.music.MusicSettings
 import org.oxycblt.auxio.music.library.RealSong
 import org.oxycblt.auxio.music.metadata.Date
@@ -231,6 +232,7 @@ private abstract class RealMediaStoreExtractor(private val context: Context) : M
                 populateMetadata(cursor, rawSong)
                 incompleteSongs.send(rawSong)
             }
+            yield()
         }
         // Free the cursor and signal that no more incomplete songs will be produced by
         // this extractor.

app/src/main/java/org/oxycblt/auxio/music/extractor/MetadataExtractor.kt

@@ -22,6 +22,7 @@ import androidx.core.text.isDigitsOnly
 import com.google.android.exoplayer2.MediaItem
 import com.google.android.exoplayer2.MetadataRetriever
 import kotlinx.coroutines.channels.Channel
+import kotlinx.coroutines.yield
 import org.oxycblt.auxio.music.library.RealSong
 import org.oxycblt.auxio.music.metadata.Date
 import org.oxycblt.auxio.music.metadata.TextTags
@@ -53,7 +54,13 @@ class MetadataExtractor(private val context: Context) {
             for (i in taskPool.indices) {
                 val task = taskPool[i]
                 if (task != null) {
-                    completeSongs.send(task.get() ?: continue)
+                    val finishedRawSong = task.get()
+                    if (finishedRawSong != null) {
+                        completeSongs.send(finishedRawSong)
+                        yield()
+                    } else {
+                        continue
+                    }
                 }
                 val result = incompleteSongs.tryReceive()
                 if (result.isClosed) {
@@ -73,6 +80,7 @@ class MetadataExtractor(private val context: Context) {
                     if (finishedRawSong != null) {
                         completeSongs.send(finishedRawSong)
                         taskPool[i] = null
+                        yield()
                     } else {
                         ongoingTasks = true
                     }

app/src/main/java/org/oxycblt/auxio/music/system/Indexer.kt

@@ -26,6 +26,7 @@ import java.util.LinkedList
 import kotlinx.coroutines.CancellationException
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.Job
 import kotlinx.coroutines.async
 import kotlinx.coroutines.channels.Channel
 import kotlinx.coroutines.launch
@@ -99,8 +100,9 @@ interface Indexer {
      * @param withCache Whether to use the cache or not when loading. If false, the cache will still
      * be written, but no cache entries will be loaded into the new library.
      * @param scope The [CoroutineScope] to run the indexing job in.
+     * @return The [Job] stacking the indexing status.
      */
-    fun index(context: Context, withCache: Boolean, scope: CoroutineScope)
+    fun index(context: Context, withCache: Boolean, scope: CoroutineScope): Job
 
     /**
      * Request that the music library should be reloaded. This should be used by components that do
@@ -293,7 +295,7 @@ private class RealIndexer : Indexer {
         this.listener = null
     }
 
-    override fun index(context: Context, withCache: Boolean, scope: CoroutineScope) {
+    override fun index(context: Context, withCache: Boolean, scope: CoroutineScope) =
         scope.launch {
             val result =
                 try {
@@ -315,7 +317,6 @@ private class RealIndexer : Indexer {
                 }
             emitCompletion(result)
         }
-    }
 
     @Synchronized
     override fun requestReindex(withCache: Boolean) {

app/src/main/java/org/oxycblt/auxio/music/system/IndexerService.kt

@@ -119,11 +119,11 @@ class IndexerService : Service(), Indexer.Controller, MusicSettings.Listener {
     override fun onStartIndexing(withCache: Boolean) {
         if (indexer.isIndexing) {
             // Cancel the previous music loading job.
-            indexScope.cancel()
+            currentIndexJob?.cancel()
             indexer.reset()
         }
         // Start a new music loading job on a co-routine.
-        indexer.index(this@IndexerService, withCache, indexScope)
+        currentIndexJob = indexer.index(this@IndexerService, withCache, indexScope)
     }
 
     override fun onIndexerStateChanged(state: Indexer.State?) {