Improve thread safety in PushManager and NotificationsManager.

// FREEBIE

Signal/src/environment/NotificationsManager.m

@@ -211,31 +211,33 @@
 
 - (void)presentNotification:(UILocalNotification *)notification identifier:(NSString *)identifier
 {
-    AssertIsOnMainThread();
-
-    // Replace any existing notification
-    // e.g. when an "Incoming Call" notification gets replaced with a "Missed Call" notification.
-    if (self.currentNotifications[identifier]) {
-        [self cancelNotificationWithIdentifier:identifier];
-    }
+    dispatch_async(dispatch_get_main_queue(), ^{
+        // Replace any existing notification
+        // e.g. when an "Incoming Call" notification gets replaced with a "Missed Call" notification.
+        if (self.currentNotifications[identifier]) {
+            [self cancelNotificationWithIdentifier:identifier];
+        }
 
-    [[UIApplication sharedApplication] scheduleLocalNotification:notification];
-    DDLogDebug(@"%@ presenting notification with identifier: %@", self.tag, identifier);
+        [[UIApplication sharedApplication] scheduleLocalNotification:notification];
+        DDLogDebug(@"%@ presenting notification with identifier: %@", self.tag, identifier);
 
-    self.currentNotifications[identifier] = notification;
+        self.currentNotifications[identifier] = notification;
+    });
 }
 
 - (void)cancelNotificationWithIdentifier:(NSString *)identifier
 {
-    AssertIsOnMainThread();
-    UILocalNotification *notification = self.currentNotifications[identifier];
-    if (!notification) {
-        DDLogWarn(@"%@ Couldn't cancel notification because none was found with identifier: %@", self.tag, identifier);
-        return;
-    }
-    [self.currentNotifications removeObjectForKey:identifier];
+    dispatch_async(dispatch_get_main_queue(), ^{
+        UILocalNotification *notification = self.currentNotifications[identifier];
+        if (!notification) {
+            DDLogWarn(
+                @"%@ Couldn't cancel notification because none was found with identifier: %@", self.tag, identifier);
+            return;
+        }
+        [self.currentNotifications removeObjectForKey:identifier];
 
-    [[UIApplication sharedApplication] cancelLocalNotification:notification];
+        [[UIApplication sharedApplication] cancelLocalNotification:notification];
+    });
 }
 
 #pragma mark - Logging

Signal/src/network/PushManager.m

@@ -431,32 +431,34 @@ NSString *const PushManagerUserInfoKeysCallBackSignalRecipientId = @"PushManager
 
 - (void)presentNotification:(UILocalNotification *)notification checkForCancel:(BOOL)checkForCancel
 {
-    OWSAssert([NSThread isMainThread]);
-
-    NSString *threadId = notification.userInfo[Signal_Thread_UserInfo_Key];
-    if (checkForCancel && threadId != nil) {
-        // The longer we wait, the more obsolete notifications we can suppress -
-        // but the more lag we introduce to notification delivery.
-        const CGFloat kDelaySeconds = 0.3f;
-        notification.fireDate = [NSDate dateWithTimeIntervalSinceNow:kDelaySeconds];
-        notification.timeZone = [NSTimeZone localTimeZone];
-    }
+    dispatch_async(dispatch_get_main_queue(), ^{
+        NSString *threadId = notification.userInfo[Signal_Thread_UserInfo_Key];
+        if (checkForCancel && threadId != nil) {
+            // The longer we wait, the more obsolete notifications we can suppress -
+            // but the more lag we introduce to notification delivery.
+            const CGFloat kDelaySeconds = 0.3f;
+            notification.fireDate = [NSDate dateWithTimeIntervalSinceNow:kDelaySeconds];
+            notification.timeZone = [NSTimeZone localTimeZone];
+        }
 
-    [[UIApplication sharedApplication] scheduleLocalNotification:notification];
-    [self.currentNotifications addObject:notification];
+        [[UIApplication sharedApplication] scheduleLocalNotification:notification];
+        [self.currentNotifications addObject:notification];
+    });
 }
 
-- (void)cancelNotificationsWithThreadId:(NSString *)threadId {
-    OWSAssert([NSThread isMainThread]);
-
-    NSMutableArray *toDelete = [NSMutableArray array];
-    [self.currentNotifications enumerateObjectsUsingBlock:^(UILocalNotification *notif, NSUInteger idx, BOOL *stop) {
-        if ([notif.userInfo[Signal_Thread_UserInfo_Key] isEqualToString:threadId]) {
-            [[UIApplication sharedApplication] cancelLocalNotification:notif];
-            [toDelete addObject:notif];
-        }
-    }];
-    [self.currentNotifications removeObjectsInArray:toDelete];
+- (void)cancelNotificationsWithThreadId:(NSString *)threadId
+{
+    dispatch_async(dispatch_get_main_queue(), ^{
+        NSMutableArray *toDelete = [NSMutableArray array];
+        [self.currentNotifications
+            enumerateObjectsUsingBlock:^(UILocalNotification *notif, NSUInteger idx, BOOL *stop) {
+                if ([notif.userInfo[Signal_Thread_UserInfo_Key] isEqualToString:threadId]) {
+                    [[UIApplication sharedApplication] cancelLocalNotification:notif];
+                    [toDelete addObject:notif];
+                }
+            }];
+        [self.currentNotifications removeObjectsInArray:toDelete];
+    });
 }
 
 + (NSString *)tag