fix: ensure background worker is scheduled when the app is dismissed (#22032)

* fix: ensure background worker is scheduled when the app is dismissed

* remove logs

* fix: use native locks (#22081)

* fix: native locks

* use atomicints

* change count check

---------

Co-authored-by: shenlong-tanwen <139912620+shalong-tanwen@users.noreply.github.com>

---------

Co-authored-by: shenlong <139912620+shenlong-tanwen@users.noreply.github.com>
Co-authored-by: shenlong-tanwen <139912620+shalong-tanwen@users.noreply.github.com>

mobile/android/app/src/main/kotlin/app/alextran/immich/ImmichApp.kt

@@ -3,6 +3,7 @@ package app.alextran.immich
 import android.app.Application
 import androidx.work.Configuration
 import androidx.work.WorkManager
+import app.alextran.immich.background.BackgroundWorkerApiImpl
 
 class ImmichApp : Application() {
   override fun onCreate() {
@@ -14,6 +15,8 @@ class ImmichApp : Application() {
     // Thus, the BackupWorker is not started. If the system kills the process after each initialization
     // (because of low memory etc.), the backup is never performed.
     // As a workaround, we also run a backup check when initializing the application
+
     ContentObserverWorker.startBackupWorker(context = this, delayMilliseconds = 0)
+    BackgroundWorkerApiImpl.enqueueBackgroundWorker(this)
   }
 }

mobile/android/app/src/main/kotlin/app/alextran/immich/MainActivity.kt

@@ -3,6 +3,7 @@ package app.alextran.immich
 import android.content.Context
 import android.os.Build
 import android.os.ext.SdkExtensions
+import app.alextran.immich.background.BackgroundEngineLock
 import app.alextran.immich.background.BackgroundWorkerApiImpl
 import app.alextran.immich.background.BackgroundWorkerFgHostApi
 import app.alextran.immich.connectivity.ConnectivityApi
@@ -25,6 +26,7 @@ class MainActivity : FlutterFragmentActivity() {
     fun registerPlugins(ctx: Context, flutterEngine: FlutterEngine) {
       flutterEngine.plugins.add(BackgroundServicePlugin())
       flutterEngine.plugins.add(HttpSSLOptionsPlugin())
+      flutterEngine.plugins.add(BackgroundEngineLock())
 
       val messenger = flutterEngine.dartExecutor.binaryMessenger
       val nativeSyncApiImpl =

mobile/android/app/src/main/kotlin/app/alextran/immich/background/BackgroundEngineLock.kt

@@ -0,0 +1,33 @@
+package app.alextran.immich.background
+
+import android.util.Log
+import androidx.work.WorkManager
+import io.flutter.embedding.engine.FlutterEngineCache
+import io.flutter.embedding.engine.plugins.FlutterPlugin
+import java.util.concurrent.atomic.AtomicInteger
+
+private const val TAG = "BackgroundEngineLock"
+
+class BackgroundEngineLock : FlutterPlugin {
+  companion object {
+    const val ENGINE_CACHE_KEY = "immich::background_worker::engine"
+    var engineCount = AtomicInteger(0)
+  }
+
+  override fun onAttachedToEngine(binding: FlutterPlugin.FlutterPluginBinding) {
+    // work manager task is running while the main app is opened, cancel the worker
+    if (engineCount.incrementAndGet() > 1 && FlutterEngineCache.getInstance()
+        .get(ENGINE_CACHE_KEY) != null
+    ) {
+      WorkManager.getInstance(binding.applicationContext)
+        .cancelUniqueWork(BackgroundWorkerApiImpl.BACKGROUND_WORKER_NAME)
+      FlutterEngineCache.getInstance().remove(ENGINE_CACHE_KEY)
+    }
+    Log.i(TAG, "Flutter engine attached. Attached Engines count: $engineCount")
+  }
+
+  override fun onDetachedFromEngine(binding: FlutterPlugin.FlutterPluginBinding) {
+    engineCount.decrementAndGet()
+    Log.i(TAG, "Flutter engine detached. Attached Engines count: $engineCount")
+  }
+}

mobile/android/app/src/main/kotlin/app/alextran/immich/background/BackgroundWorker.kt

@@ -19,6 +19,7 @@ import com.google.common.util.concurrent.ListenableFuture
 import com.google.common.util.concurrent.SettableFuture
 import io.flutter.FlutterInjector
 import io.flutter.embedding.engine.FlutterEngine
+import io.flutter.embedding.engine.FlutterEngineCache
 import io.flutter.embedding.engine.dart.DartExecutor
 import io.flutter.embedding.engine.loader.FlutterLoader
 import java.util.concurrent.TimeUnit
@@ -75,6 +76,9 @@ class BackgroundWorker(context: Context, params: WorkerParameters) :
 
     loader.ensureInitializationCompleteAsync(ctx, null, Handler(Looper.getMainLooper())) {
       engine = FlutterEngine(ctx)
+      FlutterEngineCache.getInstance().remove(BackgroundEngineLock.ENGINE_CACHE_KEY);
+      FlutterEngineCache.getInstance()
+        .put(BackgroundEngineLock.ENGINE_CACHE_KEY, engine!!)
 
       // Register custom plugins
       MainActivity.registerPlugins(ctx, engine!!)
@@ -188,6 +192,7 @@ class BackgroundWorker(context: Context, params: WorkerParameters) :
     isComplete = true
     engine?.destroy()
     engine = null
+    FlutterEngineCache.getInstance().remove(BackgroundEngineLock.ENGINE_CACHE_KEY);
     flutterApi = null
     notificationManager.cancel(NOTIFICATION_ID)
     waitForForegroundPromotion()

mobile/android/app/src/main/kotlin/app/alextran/immich/background/BackgroundWorkerApiImpl.kt

@@ -26,7 +26,7 @@ class BackgroundWorkerApiImpl(context: Context) : BackgroundWorkerFgHostApi {
   }
 
   companion object {
-    private const val BACKGROUND_WORKER_NAME = "immich/BackgroundWorkerV1"
+    const val BACKGROUND_WORKER_NAME = "immich/BackgroundWorkerV1"
     private const val OBSERVER_WORKER_NAME = "immich/MediaObserverV1"
 
     fun enqueueMediaObserver(ctx: Context) {
@@ -56,7 +56,7 @@ class BackgroundWorkerApiImpl(context: Context) : BackgroundWorkerFgHostApi {
         .setBackoffCriteria(BackoffPolicy.EXPONENTIAL, 1, TimeUnit.MINUTES)
         .build()
       WorkManager.getInstance(ctx)
-        .enqueueUniqueWork(BACKGROUND_WORKER_NAME, ExistingWorkPolicy.REPLACE, work)
+        .enqueueUniqueWork(BACKGROUND_WORKER_NAME, ExistingWorkPolicy.KEEP, work)
 
       Log.i(TAG, "Enqueued background worker with name: $BACKGROUND_WORKER_NAME")
     }