Rework flush of registration connection(s).

SignalServiceKit/src/Storage/OWSPrimaryStorage.m

@@ -138,37 +138,48 @@ void runAsyncRegistrationsForStorage(OWSStorage *storage)
 
     DDLogVerbose(@"%@ async registrations enqueued.", self.logTag);
 
-    [[self registrationConnection] asyncReadWriteWithBlock:^(YapDatabaseReadWriteTransaction *transaction) {
-        // Block until all async registrations are complete.
-        //
-        // NOTE: This has to happen on the "registration connections" for this
-        //       database.
-        NSMutableSet<YapDatabaseConnection *> *pendingRegistrationConnectionSet =
-            [[((OWSDatabase *)self.database)clearCollectedRegistrationConnections] mutableCopy];
-        DDLogVerbose(@"%@ flushing registration connections: %zd.", self.logTag, pendingRegistrationConnectionSet.count);
-
-        dispatch_async(dispatch_get_main_queue(), ^{
-            if (pendingRegistrationConnectionSet.count > 0) {
-                for (YapDatabaseConnection *dbConnection in pendingRegistrationConnectionSet) {
-                    [dbConnection
-                        flushTransactionsWithCompletionQueue:dispatch_get_main_queue()
-                                             completionBlock:^{
-                                                 OWSAssertIsOnMainThread();
-
-                                                 [pendingRegistrationConnectionSet removeObject:dbConnection];
-                                                 if (pendingRegistrationConnectionSet.count > 0) {
-                                                     DDLogVerbose(@"%@ registration connection flushed.", self.logTag);
-                                                     return;
-                                                 }
-
-                                                 [self markAsyncRegistrationsAsCompleteWithCompletion:completion];
-                                             }];
-                }
-            } else {
-                [self markAsyncRegistrationsAsCompleteWithCompletion:completion];
-            }
-        });
-    }];
+    // Flush the write queue to ensure all async registrations have begun.
+    [[self registrationConnection]
+        flushTransactionsWithCompletionQueue:dispatch_get_main_queue()
+                             completionBlock:^{
+                                 // Block until all async registrations are complete.
+                                 //
+                                 // NOTE: This has to happen on the "registration connections" for this
+                                 //       database.
+                                 NSMutableSet<YapDatabaseConnection *> *pendingRegistrationConnectionSet = [
+                                     [((OWSDatabase *)self.database)clearCollectedRegistrationConnections] mutableCopy];
+                                 DDLogVerbose(@"%@ flushing registration connections: %zd.",
+                                     self.logTag,
+                                     pendingRegistrationConnectionSet.count);
+
+                                 dispatch_async(dispatch_get_main_queue(), ^{
+                                     if (pendingRegistrationConnectionSet.count > 0) {
+                                         for (YapDatabaseConnection *dbConnection in pendingRegistrationConnectionSet) {
+                                             [dbConnection
+                                                 flushTransactionsWithCompletionQueue:dispatch_get_main_queue()
+                                                                      completionBlock:^{
+                                                                          OWSAssertIsOnMainThread();
+
+                                                                          [pendingRegistrationConnectionSet
+                                                                              removeObject:dbConnection];
+                                                                          if (pendingRegistrationConnectionSet.count
+                                                                              > 0) {
+                                                                              DDLogVerbose(@"%@ registration "
+                                                                                           @"connection flushed.",
+                                                                                  self.logTag);
+                                                                              return;
+                                                                          }
+
+                                                                          [self
+                                                                              markAsyncRegistrationsAsCompleteWithCompletion:
+                                                                                  completion];
+                                                                      }];
+                                         }
+                                     } else {
+                                         [self markAsyncRegistrationsAsCompleteWithCompletion:completion];
+                                     }
+                                 });
+                             }];
 }
 
 - (void)markAsyncRegistrationsAsCompleteWithCompletion:(void (^_Nonnull)(void))completion