Use a temporary app object and database lock to avoid saving while the database is not in a consistent state

Limelight/Database/DataManager.h

@@ -11,6 +11,7 @@
 #import "AppDelegate.h"
 #import "Host.h"
 #import "App.h"
+#import "TemporaryApp.h"
 
 @interface DataManager : NSObject
 
@@ -22,7 +23,7 @@
 - (void) saveData;
 - (Host*) createHost;
 - (void) removeHost:(Host*)host;
-- (App*) createApp;
-- (void) removeApp:(App*)app;
+- (App*) addAppFromTemporaryApp:(TemporaryApp*)tempApp;
+- (void) removeAppFromHost:(App*)app;
 
 @end

Limelight/Database/DataManager.m

@@ -7,9 +7,18 @@
 //
 
 #import "DataManager.h"
+#import "TemporaryApp.h"
 
 @implementation DataManager
 
++ (NSObject *)databaseLock {
+    static NSObject *lock = nil;
+    if (lock == nil) {
+        lock = [[NSObject alloc] init];
+    }
+    return lock;
+}
+
 - (id) init {
     self = [super init];
     self.appDelegate = [[UIApplication sharedApplication] delegate];
@@ -57,38 +66,65 @@
 }
 
 - (void) saveData {
-    NSError* error;
-    if (![[self.appDelegate managedObjectContext] save:&error]) {
-        Log(LOG_E, @"Unable to save hosts to database: %@", error);
+    @synchronized([DataManager databaseLock]) {
+        NSError* error;
+        if (![[self.appDelegate managedObjectContext] save:&error]) {
+            Log(LOG_E, @"Unable to save hosts to database: %@", error);
+        }
+        [self.appDelegate saveContext];
     }
-    [self.appDelegate saveContext];
 }
 
 - (NSArray*) retrieveHosts {
     return [self fetchRecords:@"Host"];
 }
 
-- (App*) createApp {
-    NSEntityDescription* entity = [NSEntityDescription entityForName:@"App" inManagedObjectContext:[self.appDelegate managedObjectContext]];
-    return [[App alloc] initWithEntity:entity insertIntoManagedObjectContext:[self.appDelegate managedObjectContext]];
+- (App*) addAppFromTemporaryApp:(TemporaryApp*)tempApp {
+    
+    App* managedApp;
+    
+    @synchronized([DataManager databaseLock]) {
+        NSEntityDescription* entity = [NSEntityDescription entityForName:@"App" inManagedObjectContext:[self.appDelegate managedObjectContext]];
+        managedApp = [[App alloc] initWithEntity:entity insertIntoManagedObjectContext:[self.appDelegate managedObjectContext]];
+        
+        assert(tempApp.host != nil);
+        
+        managedApp.id = tempApp.id;
+        managedApp.image = tempApp.image;
+        managedApp.name = tempApp.name;
+        managedApp.isRunning = tempApp.isRunning;
+        managedApp.host = tempApp.host;
+        
+        [managedApp.host addAppListObject:managedApp];
+    }
+    
+    return managedApp;
 }
 
-- (void) removeApp:(App*)app {
-    [[self.appDelegate managedObjectContext] deleteObject:app];
+- (void) removeAppFromHost:(App*)app {
+    @synchronized([DataManager databaseLock]) {
+        assert(app.host != nil);
+        
+        [app.host removeAppListObject:app];
+        [[self.appDelegate managedObjectContext] deleteObject:app];
+    }
 }
 
 - (NSArray*) fetchRecords:(NSString*)entityName {
-    NSFetchRequest* fetchRequest = [[NSFetchRequest alloc] init];
-    NSEntityDescription* entity = [NSEntityDescription entityForName:entityName inManagedObjectContext:[self.appDelegate managedObjectContext]];
-    [fetchRequest setEntity:entity];
-    [fetchRequest setAffectedStores:[NSArray arrayWithObjects:[[self.appDelegate persistentStoreCoordinator] persistentStoreForURL:[self.appDelegate getStoreURL]], nil]];
+    NSArray* fetchedRecords;
     
-    NSError* error;
-    NSArray* fetchedRecords = [[self.appDelegate managedObjectContext] executeFetchRequest:fetchRequest error:&error];
-    //TODO: handle errors
+    @synchronized([DataManager databaseLock]) {
+        NSFetchRequest* fetchRequest = [[NSFetchRequest alloc] init];
+        NSEntityDescription* entity = [NSEntityDescription entityForName:entityName inManagedObjectContext:[self.appDelegate managedObjectContext]];
+        [fetchRequest setEntity:entity];
+        [fetchRequest setAffectedStores:[NSArray arrayWithObjects:[[self.appDelegate persistentStoreCoordinator] persistentStoreForURL:[self.appDelegate getStoreURL]], nil]];
+        
+        NSError* error;
+        fetchedRecords = [[self.appDelegate managedObjectContext] executeFetchRequest:fetchRequest error:&error];
+        //TODO: handle errors
+    }
     
     return fetchedRecords;
-    
 }
 
 @end

Limelight/Database/TemporaryApp.h

@@ -0,0 +1,20 @@
+//
+//  TemporaryApp.h
+//  Moonlight
+//
+//  Created by Cameron Gutman on 9/30/15.
+//  Copyright © 2015 Moonlight Stream. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+#import "Host.h"
+
+@interface TemporaryApp : NSObject
+
+@property (nullable, nonatomic, retain) NSString *id;
+@property (nullable, nonatomic, retain) NSData *image;
+@property (nullable, nonatomic, retain) NSString *name;
+@property (nonatomic) BOOL isRunning;
+@property (nullable, nonatomic, retain) Host *host;
+
+@end

Limelight/Database/TemporaryApp.m

@@ -0,0 +1,13 @@
+//
+//  TemporaryApp.m
+//  Moonlight
+//
+//  Created by Cameron Gutman on 9/30/15.
+//  Copyright © 2015 Moonlight Stream. All rights reserved.
+//
+
+#import "TemporaryApp.h"
+
+@implementation TemporaryApp
+
+@end

Limelight/Network/AppListResponse.m

@@ -7,7 +7,7 @@
 //
 
 #import "AppListResponse.h"
-#import "App.h"
+#import "TemporaryApp.h"
 #import "DataManager.h"
 #import <libxml2/libxml/xmlreader.h>
 
@@ -60,7 +60,6 @@ static const char* TAG_APP_IS_RUNNING = "IsRunning";
     self.statusMessage = statusMsg;
     
     node = node->children;
-    DataManager* dataMan = [[DataManager alloc] init];
     
     while (node != NULL) {
         //Log(LOG_D, @"node: %s", node->name);
@@ -96,7 +95,7 @@ static const char* TAG_APP_IS_RUNNING = "IsRunning";
                 appInfoNode = appInfoNode->next;
             }
             if (appId != nil) {
-                App* app = [dataMan createApp];
+                TemporaryApp* app = [[TemporaryApp alloc] init];
                 app.name = appName;
                 app.id = appId;
                 app.isRunning = appIsRunning;

Limelight/ViewControllers/MainFrameViewController.m

@@ -23,6 +23,7 @@
 #import "StreamFrameViewController.h"
 #import "LoadingFrameViewController.h"
 #import "ComputerScrollView.h"
+#import "TemporaryApp.h"
 
 @implementation MainFrameViewController {
     NSOperationQueue* _opQueue;
@@ -141,7 +142,7 @@ static NSMutableSet* hostList;
 
 - (void) mergeAppLists:(NSArray*) newList forHost:(Host*)host {
     DataManager* database = [[DataManager alloc] init];
-    for (App* app in newList) {
+    for (TemporaryApp* app in newList) {
         BOOL appAlreadyInList = NO; 
         for (App* savedApp in host.appList) {
             if ([app.id isEqualToString:savedApp.id]) {
@@ -152,9 +153,7 @@ static NSMutableSet* hostList;
         }
         if (!appAlreadyInList) {
             app.host = host;
-            [host addAppListObject:app];
-        } else {
-            [database removeApp:app];
+            [database addAppFromTemporaryApp:app];
         }
     }
     
@@ -167,8 +166,7 @@ static NSMutableSet* hostList;
             }
         }
         if (appWasRemoved) {
-            [host removeAppListObject:app];
-            [database removeApp:app];
+            [database removeAppFromHost:app];
         }
     }
     [database saveData];