Fix race in CVM startup.

Signal/src/ViewControllers/ConversationView/ConversationViewController.m

@@ -4346,6 +4346,11 @@ typedef enum : NSUInteger {
 
 #pragma mark - ConversationViewModelDelegate
 
+- (BOOL)isObservingVMUpdates
+{
+    return self.shouldObserveVMUpdates;
+}
+
 - (void)conversationViewModelWillUpdate
 {
     OWSAssertIsOnMainThread();

Signal/src/ViewControllers/ConversationView/ConversationViewModel.h

@@ -69,8 +69,7 @@ typedef NS_ENUM(NSUInteger, ConversationUpdateItemType) {
 - (void)conversationViewModelDidLoadPrevPage;
 - (void)conversationViewModelRangeDidChange;
 
-// TODO: It'd be nice to remove this.
-- (BOOL)shouldObserveDBModifications;
+- (BOOL)isObservingVMUpdates;
 
 - (ConversationStyle *)conversationStyle;
 

Signal/src/ViewControllers/ConversationView/ConversationViewModel.m

@@ -210,18 +210,6 @@ static const int kYapDatabaseRangeMinLength = 0;
 
 - (void)addNotificationListeners
 {
-    [[NSNotificationCenter defaultCenter] addObserver:self
-                                             selector:@selector(uiDatabaseDidUpdateExternally:)
-                                                 name:OWSUIDatabaseConnectionDidUpdateExternallyNotification
-                                               object:self.primaryStorage.dbNotificationObject];
-    [[NSNotificationCenter defaultCenter] addObserver:self
-                                             selector:@selector(uiDatabaseWillUpdate:)
-                                                 name:OWSUIDatabaseConnectionWillUpdateNotification
-                                               object:self.primaryStorage.dbNotificationObject];
-    [[NSNotificationCenter defaultCenter] addObserver:self
-                                             selector:@selector(uiDatabaseDidUpdate:)
-                                                 name:OWSUIDatabaseConnectionDidUpdateNotification
-                                               object:self.primaryStorage.dbNotificationObject];
     [[NSNotificationCenter defaultCenter] addObserver:self
                                              selector:@selector(applicationDidEnterBackground:)
                                                  name:OWSApplicationDidEnterBackgroundNotification
@@ -259,6 +247,19 @@ static const int kYapDatabaseRangeMinLength = 0;
     if (![self reloadViewItems]) {
         OWSFailDebug(@"failed to reload view items in configureForThread.");
     }
+
+    [[NSNotificationCenter defaultCenter] addObserver:self
+                                             selector:@selector(uiDatabaseDidUpdateExternally:)
+                                                 name:OWSUIDatabaseConnectionDidUpdateExternallyNotification
+                                               object:self.primaryStorage.dbNotificationObject];
+    [[NSNotificationCenter defaultCenter] addObserver:self
+                                             selector:@selector(uiDatabaseWillUpdate:)
+                                                 name:OWSUIDatabaseConnectionWillUpdateNotification
+                                               object:self.primaryStorage.dbNotificationObject];
+    [[NSNotificationCenter defaultCenter] addObserver:self
+                                             selector:@selector(uiDatabaseDidUpdate:)
+                                                 name:OWSUIDatabaseConnectionDidUpdateNotification
+                                               object:self.primaryStorage.dbNotificationObject];
 }
 
 - (void)viewDidLoad
@@ -458,19 +459,24 @@ static const int kYapDatabaseRangeMinLength = 0;
 
     OWSLogVerbose(@"");
 
-    if (self.delegate.shouldObserveDBModifications) {
-        // External database modifications can't be converted into incremental updates,
-        // so rebuild everything.  This is expensive and usually isn't necessary, but
-        // there's no alternative.
-        //
-        // We don't need to do this if we're not observing db modifications since we'll
-        // do it when we resume.
-        [self resetMappings];
+    if (!self.delegate.isObservingVMUpdates) {
+        return;
     }
+
+    // External database modifications can't be converted into incremental updates,
+    // so rebuild everything.  This is expensive and usually isn't necessary, but
+    // there's no alternative.
+    //
+    // We don't need to do this if we're not observing db modifications since we'll
+    // do it when we resume.
+    [self resetMappings];
 }
 
 - (void)uiDatabaseWillUpdate:(NSNotification *)notification
 {
+    if (!self.delegate.isObservingVMUpdates) {
+        return;
+    }
     [self.delegate conversationViewModelWillUpdate];
 }
 
@@ -618,6 +624,13 @@ static const int kYapDatabaseRangeMinLength = 0;
     OWSAssertDebug(oldItemIdList);
     OWSAssertDebug(updatedItemSet);
 
+    if (!self.delegate.isObservingVMUpdates) {
+        OWSFailDebug(@"Skipping VM update.");
+        // We fire this event, but it will be ignored.
+        [self.delegate conversationViewModelDidUpdate:ConversationUpdate.minorUpdate];
+        return;
+    }
+
     if (oldItemIdList.count != [NSSet setWithArray:oldItemIdList].count) {
         OWSFailDebug(@"Old view item list has duplicates.");
         [self.delegate conversationViewModelDidUpdate:ConversationUpdate.reloadUpdate];