android: updates - no stuck Downloading state, thread-safe singleton

After a silent pre-download the state stayed Downloading, so tapping the
"update ready" notification did nothing. It now returns to Available;
an install request without a known update (e.g. after a process restart)
re-checks and installs when found.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/frontends/android/app/src/main/java/org/strongswan/android/logic/updates/UpdateManager.kt

@@ -116,12 +116,18 @@ class UpdateManager private constructor(private val context: Context)
 		private const val UPDATES_NOTIFICATION_ID = 1001
 		private const val UPDATES_PROGRESS_NOTIFICATION_ID = 1002
 
+		@Volatile
 		private var mInstance: UpdateManager? = null
 
+		/* called from the main thread and the WorkManager thread: a second
+		 * instance would run its own check loop and state */
 		@JvmStatic
 		fun getInstance(context: Context): UpdateManager
 		{
-			return mInstance ?: UpdateManager(context.applicationContext).also { mInstance = it }
+			return mInstance ?: synchronized(this)
+			{
+				mInstance ?: UpdateManager(context.applicationContext).also { mInstance = it }
+			}
 		}
 
 		/**
@@ -154,6 +160,10 @@ class UpdateManager private constructor(private val context: Context)
 
 	private var mCheckJob: Job? = null
 	private var mDownloadJob: Job? = null
+	/* the user asked to install (e.g. tapped "update ready") while no update
+	 * was known in this process: install as soon as the check finds it */
+	@Volatile
+	private var mInstallPending = false
 	private var mVpnService: VpnStateService? = null
 
 	private val mConnection = object : ServiceConnection
@@ -228,6 +238,7 @@ class UpdateManager private constructor(private val context: Context)
 		check()
 	}
 
+	@Synchronized
 	private fun check()
 	{
 		if (mCheckJob?.isActive == true || mDownloadJob?.isActive == true)
@@ -236,17 +247,29 @@ class UpdateManager private constructor(private val context: Context)
 		}
 		mCheckJob = mScope.launch {
 			mState.value = UpdateState.Checking
-			val info = fetchManifest() ?: return@launch
+			val info = fetchManifest() ?: run {
+				mInstallPending = false
+				return@launch
+			}
 			mPrefs.edit().putLong(Constants.PREF_LAST_UPDATE_CHECK, System.currentTimeMillis()).apply()
 			if (info.versionCode > currentVersionCode())
 			{
 				DiagLog.i(TAG, "update: available ${info.versionName} (${info.versionCode}), " +
 					"installed ${currentVersionName()} (${currentVersionCode()})")
 				mState.value = UpdateState.Available(info)
-				maybeDownloadSilently(info)
+				if (mInstallPending)
+				{
+					mInstallPending = false
+					downloadAndInstall()
+				}
+				else
+				{
+					maybeDownloadSilently(info)
+				}
 			}
 			else
 			{
+				mInstallPending = false
 				DiagLog.i(TAG, "update: up to date (${currentVersionName()} ${currentVersionCode()})")
 				mState.value = UpdateState.UpToDate
 			}
@@ -260,6 +283,7 @@ class UpdateManager private constructor(private val context: Context)
 	 * right away; otherwise a notification tells the user it is ready - one
 	 * tap installs it (a single system confirmation on Android < 12)
 	 */
+	@Synchronized
 	private fun maybeDownloadSilently(info: UpdateInfo)
 	{
 		if (!isSilentUpdatesEnabled())
@@ -292,7 +316,19 @@ class UpdateManager private constructor(private val context: Context)
 				else
 				{
 					DiagLog.i(TAG, "update: ${info.versionName} downloaded, waiting for the user")
-					notifyUpdateReady(info)
+					/* back to Available: Downloading would block downloadAndInstall()
+					 * and leave the settings row stuck at 100% */
+					mState.value = UpdateState.Available(info)
+					if (mInstallPending)
+					{
+						mInstallPending = false
+						UpdateInstaller.install(context, apk)
+						mState.value = UpdateState.Idle
+					}
+					else
+					{
+						notifyUpdateReady(info)
+					}
 				}
 			}
 			catch (e: Exception)
@@ -300,6 +336,7 @@ class UpdateManager private constructor(private val context: Context)
 				Log.e(TAG, "Silent update download failed", e)
 				DiagLog.i(TAG, "update: silent download failed: ${e.javaClass.simpleName}: ${e.message}")
 				/* the manual download from the settings screen still works */
+				mState.value = UpdateState.Available(info)
 			}
 		}
 	}
@@ -434,11 +471,20 @@ class UpdateManager private constructor(private val context: Context)
 	 * Downloads the update APK (with progress) and installs it as an
 	 * in-place update (the app data is preserved)
 	 */
+	@Synchronized
 	fun downloadAndInstall()
 	{
-		val info = (mState.value as? UpdateState.Available)?.info ?: return
 		if (mDownloadJob?.isActive == true)
-		{
+		{	/* a silent download is running: install once it is done */
+			mInstallPending = true
+			return
+		}
+		val info = (mState.value as? UpdateState.Available)?.info
+		if (info == null)
+		{	/* e.g. the "update ready" notification was tapped after the process
+			 * restarted: look the update up again and install it when found */
+			mInstallPending = true
+			check()
 			return
 		}
 		mDownloadJob = mScope.launch {