[Core, Android] Fix to address the elusive 'Sharing violation on path…

… PropertyStore.forms.tmp' (xamarin#1075) * use a semaphor for actual saving piece make reading serialized propertystore readonly to help with collisions. * change over to async Task and await OnStateChanged() method to try and mitigate what might be the race condition causing the ' Sharing violation on path PropertyStore.forms.tmp' error * update Semaphore name * remove private specifier per the style guide * Update docs and add warning suppression for broken mono warning * ... and adding the warning suppression to Release mode, as well. * -add try...finally block so we can guarantee that the semaphore is released if there's an exception while saving the properties. -remove the legacy code that the semaphore replaces * Update docs * Attempting to fix docs * Trying again to get docs to pass
yone64 · Oct 3, 2017 · afa0fb7 · afa0fb7
1 parent 6877d63
commit afa0fb7
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Showing 5 changed files with 45 additions and 39 deletions.
diff --git a/Xamarin.Forms.Core/Application.cs b/Xamarin.Forms.Core/Application.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
+using System.Threading;
 using System.ComponentModel;
 using System.Threading.Tasks;
 using Xamarin.Forms.Internals;
@@ -15,14 +16,13 @@ public class Application : Element, IResourcesProvider, IApplicationController,
 		readonly Lazy<PlatformConfigurationRegistry<Application>> _platformConfigurationRegistry;
 
 		IAppIndexingProvider _appIndexProvider;
-		bool _isSaving;
 
 		ReadOnlyCollection<Element> _logicalChildren;
 
 		Page _mainPage;
 
 		ResourceDictionary _resources;
-		bool _saveAgain;
+		static SemaphoreSlim SaveSemaphore = new SemaphoreSlim(1, 1);
 
 		protected Application()
 		{
@@ -309,16 +309,16 @@ void OnPopCanceled()
 
 		async Task SetPropertiesAsync()
 		{
-			if (_isSaving)
-			{
-				_saveAgain = true;
-				return;
-			}
-			_isSaving = true;
-			await DependencyService.Get<IDeserializer>().SerializePropertiesAsync(Properties);
-			if (_saveAgain)
-				await DependencyService.Get<IDeserializer>().SerializePropertiesAsync(Properties);
-			_isSaving = _saveAgain = false;
+			await SaveSemaphore.WaitAsync();
+            try
+            {
+                await DependencyService.Get<IDeserializer>().SerializePropertiesAsync(Properties);
+            }
+            finally
+            {
+                SaveSemaphore.Release();
+            }
+
 		}
 
 		class NavigationImpl : NavigationProxy

diff --git a/Xamarin.Forms.Platform.Android/AppCompat/FormsAppCompatActivity.cs b/Xamarin.Forms.Platform.Android/AppCompat/FormsAppCompatActivity.cs
@@ -22,6 +22,7 @@
 using AlertDialog = Android.Support.V7.App.AlertDialog;
 using ARelativeLayout = Android.Widget.RelativeLayout;
 using Xamarin.Forms.Internals;
+using System.Threading.Tasks;
 
 #endregion
 
@@ -162,7 +163,7 @@ protected override void OnActivityResult(int requestCode, Result resultCode, Int
 				callback(resultCode, data);
 		}
 
-		protected override void OnCreate(Bundle savedInstanceState)
+		protected override async void OnCreate(Bundle savedInstanceState)
 		{
 			if (!AllowFragmentRestore)
 			{
@@ -194,7 +195,7 @@ protected override void OnCreate(Bundle savedInstanceState)
 			_previousState = _currentState;
 			_currentState = AndroidApplicationLifecycleState.OnCreate;
 
-			OnStateChanged();
+			await OnStateChanged();
 
 			if (Forms.IsLollipopOrNewer)
 			{
@@ -221,7 +222,7 @@ protected override void OnNewIntent(Intent intent)
 			CheckForAppLink(intent);
 		}
 
-		protected override void OnPause()
+		protected override async void OnPause()
 		{
 			_layout.HideKeyboard(true);
 
@@ -234,20 +235,20 @@ protected override void OnPause()
 			_previousState = _currentState;
 			_currentState = AndroidApplicationLifecycleState.OnPause;
 
-			OnStateChanged();
+			await OnStateChanged();
 		}
 
-		protected override void OnRestart()
+		protected override async void OnRestart()
 		{
 			base.OnRestart();
 
 			_previousState = _currentState;
 			_currentState = AndroidApplicationLifecycleState.OnRestart;
 
-			OnStateChanged();
+			await OnStateChanged();
 		}
 
-		protected override void OnResume()
+		protected override async void OnResume()
 		{
 			// counterpart to OnPause
 			base.OnResume();
@@ -263,24 +264,24 @@ protected override void OnResume()
 			_previousState = _currentState;
 			_currentState = AndroidApplicationLifecycleState.OnResume;
 
-			OnStateChanged();
+			await OnStateChanged();
 		}
 
-		protected override void OnStart()
+		protected override async void OnStart()
 		{
 			base.OnStart();
 
 			_previousState = _currentState;
 			_currentState = AndroidApplicationLifecycleState.OnStart;
 
-			OnStateChanged();
+			await OnStateChanged();
 		}
 
 		// Scenarios that stop and restart your app
 		// -- Switches from your app to another app, activity restarts when clicking on the app again.
 		// -- Action in your app that starts a new Activity, the current activity is stopped and the second is created, pressing back restarts the activity
 		// -- The user receives a phone call while using your app on his or her phone
-		protected override void OnStop()
+		protected override async void OnStop()
 		{
 			// writing to storage happens here!
 			// full UI obstruction
@@ -293,7 +294,7 @@ protected override void OnStop()
 			_previousState = _currentState;
 			_currentState = AndroidApplicationLifecycleState.OnStop;
 
-			OnStateChanged();
+			await OnStateChanged();
 		}
 
 		void AppOnPropertyChanged(object sender, PropertyChangedEventArgs args)
@@ -380,7 +381,7 @@ void OnPageBusy(Page sender, bool enabled)
 			UpdateProgressBarVisibility(_busyCount > 0);
 		}
 
-		async void OnStateChanged()
+		async Task OnStateChanged()
 		{
 			if (_application == null)
 				return;

diff --git a/Xamarin.Forms.Platform.Android/Deserializer.cs b/Xamarin.Forms.Platform.Android/Deserializer.cs
@@ -20,22 +20,28 @@ public Task<IDictionary<string, object>> DeserializePropertiesAsync()
 			return Task.Run(() =>
 			{
 				using (IsolatedStorageFile store = IsolatedStorageFile.GetUserStoreForApplication())
-				using (IsolatedStorageFileStream stream = store.OpenFile(PropertyStoreFile, System.IO.FileMode.OpenOrCreate))
-				using (XmlDictionaryReader reader = XmlDictionaryReader.CreateBinaryReader(stream, XmlDictionaryReaderQuotas.Max))
 				{
-					if (stream.Length == 0)
+					if (!store.FileExists(PropertyStoreFile))
 						return null;
 
-					try
+					using (IsolatedStorageFileStream stream = store.OpenFile(PropertyStoreFile, System.IO.FileMode.Open, System.IO.FileAccess.Read))
+					using (XmlDictionaryReader reader = XmlDictionaryReader.CreateBinaryReader(stream, XmlDictionaryReaderQuotas.Max))
 					{
-						var dcs = new DataContractSerializer(typeof(Dictionary<string, object>));
-						return (IDictionary<string, object>)dcs.ReadObject(reader);
-					}
-					catch (Exception e)
-					{
-						Debug.WriteLine("Could not deserialize properties: " + e.Message);
-						Log.Warning("Xamarin.Forms PropertyStore", $"Exception while reading Application properties: {e}");
+						if (stream.Length == 0)
+							return null;
+
+						try
+						{
+							var dcs = new DataContractSerializer(typeof(Dictionary<string, object>));
+							return (IDictionary<string, object>)dcs.ReadObject(reader);
+						}
+						catch (Exception e)
+						{
+							Debug.WriteLine("Could not deserialize properties: " + e.Message);
+							Log.Warning("Xamarin.Forms PropertyStore", $"Exception while reading Application properties: {e}");
+						}
 					}
+
 				}
 
 				return null;

diff --git a/Xamarin.Forms.Platform.Android/Xamarin.Forms.Platform.Android.csproj b/Xamarin.Forms.Platform.Android/Xamarin.Forms.Platform.Android.csproj
@@ -42,8 +42,7 @@
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
-    <NoWarn>
-    </NoWarn>
+    <NoWarn>CS0109</NoWarn>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)' == 'Turkey|AnyCPU'">
     <DebugSymbols>true</DebugSymbols>

diff --git a/docs/Xamarin.Forms.Core/Xamarin.Forms/Application.xml b/docs/Xamarin.Forms.Core/Xamarin.Forms/Application.xml
@@ -455,7 +455,7 @@
           <AttributeName>System.Diagnostics.DebuggerStepThrough</AttributeName>
         </Attribute>
         <Attribute>
-          <AttributeName>System.Runtime.CompilerServices.AsyncStateMachine(typeof(Xamarin.Forms.Application/&lt;SavePropertiesAsync&gt;d__53))</AttributeName>
+          <AttributeName>System.Runtime.CompilerServices.AsyncStateMachine(typeof(Xamarin.Forms.Application/&lt;SavePropertiesAsync&gt;d__52))</AttributeName>
         </Attribute>
       </Attributes>
       <ReturnValue>