Prevent multiple installation sessions running in parallel

app/src/main/java/com/topjohnwu/magisk/core/tasks/MagiskInstaller.kt

@@ -43,6 +43,8 @@ import java.security.SecureRandom
 import java.util.*
 import java.util.zip.ZipFile
 
+private var haveActiveSession: Boolean = false
+
 abstract class MagiskInstallImpl protected constructor(
     protected val console: MutableList<String> = NOPList.getInstance(),
     private val logs: MutableList<String> = NOPList.getInstance()
@@ -415,7 +417,18 @@ abstract class MagiskInstallImpl protected constructor(
     @WorkerThread
     protected abstract suspend fun operations(): Boolean
 
-    open suspend fun exec() = withContext(Dispatchers.IO) { operations() }
+    open suspend fun exec(): Boolean {
+        synchronized(haveActiveSession) {
+            if (haveActiveSession)
+                return false
+            haveActiveSession = true
+        }
+        val result = withContext(Dispatchers.IO) { operations() }
+        synchronized(haveActiveSession) {
+            haveActiveSession = false
+        }
+        return result
+    }
 }
 
 abstract class MagiskInstaller(

app/src/main/java/com/topjohnwu/magisk/ui/flash/FlashFragment.kt

@@ -50,6 +50,7 @@ class FlashFragment : BaseUIFragment<FlashViewModel, FragmentFlashMd2Binding>()
 
         defaultOrientation = activity.requestedOrientation
         activity.requestedOrientation = ActivityInfo.SCREEN_ORIENTATION_NOSENSOR
+        viewModel.startFlashing()
     }
 
     @SuppressLint("WrongConstant")

app/src/main/java/com/topjohnwu/magisk/ui/flash/FlashViewModel.kt

@@ -1,6 +1,5 @@
 package com.topjohnwu.magisk.ui.flash
 
-import android.net.Uri
 import android.view.MenuItem
 import androidx.databinding.Bindable
 import androidx.lifecycle.LiveData
@@ -27,7 +26,7 @@ import com.topjohnwu.superuser.Shell
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.launch
 
-class FlashViewModel(args: FlashFragmentArgs) : BaseViewModel() {
+class FlashViewModel(private val args: FlashFragmentArgs) : BaseViewModel() {
 
     @get:Bindable
     var showReboot = Shell.rootAccess()
@@ -49,14 +48,11 @@ class FlashViewModel(args: FlashFragmentArgs) : BaseViewModel() {
         }
     }
 
-    init {
+    fun startFlashing() {
         val (action, uri, id) = args
         if (id != -1)
             Notifications.mgr.cancel(id)
-        startFlashing(action, uri)
-    }
 
-    private fun startFlashing(action: String, uri: Uri?) {
         viewModelScope.launch {
             val result = when (action) {
                 Const.Value.FLASH_ZIP -> {