fix(*): Make sure start/track, UI, callbacks are not run in background

In some occasion UI and callbacks was running in background. This commit prevents it. Also protects against misuse of start/track.

JIRA: LP-5794

Author: alexisoyama

Leanplum-SDK/Classes/LPEventCallbackManager.m

@@ -84,6 +84,14 @@ + (void)invokeSuccessCallbacksOnResponses:(id)responses
                                  requests:(NSArray *)requests
                                 operation:(id<LPNetworkOperationProtocol>)operation
 {
+    // Ensure all callbacks are on main thread.
+    if (![NSThread isMainThread]) {
+        dispatch_sync(dispatch_get_main_queue(), ^{
+            [self invokeSuccessCallbacksOnResponses:responses requests:requests operation:operation];
+        });
+        return;
+    }
+    
     // Invoke and remove the callbacks that have errors.
     [LPEventCallbackManager invokeErrorCallbacksOnResponses:responses];
 
@@ -117,6 +125,14 @@ + (void)invokeSuccessCallbacksOnResponses:(id)responses
 
 + (void)invokeErrorCallbacksOnResponses:(id)responses
 {
+    // Ensure all callbacks are on main thread.
+    if (![NSThread isMainThread]) {
+        dispatch_sync(dispatch_get_main_queue(), ^{
+            [self invokeErrorCallbacksOnResponses:responses];
+        });
+        return;
+    }
+    
     // Handle errors that don't return an HTTP error code.
     NSMutableDictionary *callbackMap = [LPEventCallbackManager eventCallbackMap];
     for (NSUInteger i = 0; i < [LPResponse numResponsesInDictionary:responses]; i++) {

Leanplum-SDK/Classes/LPMessageTemplates.m

@@ -568,6 +568,14 @@ + (UIImage *)dismissImage:(UIColor *)color withSize:(int)size
 // Displays the Center Popup, Interstitial and Web Interstitial.
 - (void)showPopup
 {
+    // UI can't be modified in background.
+    if (![NSThread isMainThread]) {
+        dispatch_sync(dispatch_get_main_queue(), ^{
+            [self showPopup];
+        });
+        return;
+    }
+    
     LPActionContext *context = _contexts.lastObject;
     BOOL isFullscreen = [context.actionName isEqualToString:LPMT_INTERSTITIAL_NAME];
     BOOL isWeb = [context.actionName isEqualToString:LPMT_WEB_INTERSTITIAL_NAME] ||
@@ -717,6 +725,14 @@ - (void)closePopupWithAnimation:(BOOL)animated
         return;
     }
 
+    // UI can't be modified in background.
+    if (![NSThread isMainThread]) {
+        dispatch_sync(dispatch_get_main_queue(), ^{
+            [self closePopupWithAnimation:animated actionNamed:actionName track:track];
+        });
+        return;
+    }
+    
     LPActionContext *context = _contexts.lastObject;
     [_contexts removeLastObject];
 

Leanplum-SDK/Classes/Leanplum.m

@@ -725,6 +725,15 @@ + (void)startWithUserId:(NSString *)userId
          @"methods."];
         return;
     }
+    
+    // Leanplum should not be started in background.
+    if (![NSThread isMainThread]) {
+        dispatch_sync(dispatch_get_main_queue(), ^{
+            [self startWithUserId:userId userAttributes:attributes responseHandler:startResponse];
+        });
+        return;
+    }
+    
     LP_TRY
     NSDate *startTime = [NSDate date];
     if (startResponse) {
@@ -1844,6 +1853,15 @@ + (void)track:(NSString *)event withValue:(double)value andInfo:(NSString *)info
 {
     RETURN_IF_NOOP;
     LP_TRY
+    
+    // Track should not be called in background.
+    if (![NSThread isMainThread]) {
+        dispatch_sync(dispatch_get_main_queue(), ^{
+            [self track:event withValue:value andInfo:info andArgs:args andParameters:params];
+        });
+        return;
+    }
+    
     NSString *valueStr = [NSString stringWithFormat:@"%f", value];
     NSMutableDictionary *arguments = [NSMutableDictionary dictionaryWithObjectsAndKeys:
                                  valueStr, LP_PARAM_VALUE, nil];