Exception when adding multiple documents to Realm via loop

[markstratman]

SDK and version

SDK : .Net Realm 10.20.0

Observations

1. SubscribeForNotifications
2. Performed 1000 adds via a loop, received the first 61 events the received crash report

Not always producible, about half the time a failure occures.

Crash log / stacktrace

D:\a\realm-dotnet\realm-dotnet\wrappers\realm-core\src\realm\alloc_slab.cpp:531: [realm-core-13.4.0] Assertion failed: ref + size <= next->first with (ref, size, next->first, next->second, get_file_path_for_assertions()) = [489768, 56, 489768, 56, "C:\Users\stratman\Documents\mongodb-realm\fleetproxy-szmau\64124734058eecc495c4658a\default.realm"]
!!! IMPORTANT: Please report this at https://github.com/realm/realm-core/issues/new/choose

C:\repo-git\wss\fleet-proxy\poc\dotnet\RealmClientConsole\RealmClientConsole\bin\Debug\net7\RealmClientConsole.exe (process 38392) exited with code -1073740791.

Steps & Code to Reproduce

        { 
            try
            {
                var realm = await GetRealmAsync();
                realm.Subscriptions.Update(() =>
                {
                    var myMoes = realm
                        .All<Moe>()
                        .Where(m => m.WjaProxyId == CurrentUser.Id);

                    myMoes
                        .SubscribeForNotifications(async (moes, changes, error) =>
                        {
                            try
                            {
                                if (changes != null)
                                {
                                    Console.ForegroundColor = ConsoleColor.Magenta;
                                    foreach (var i in changes.DeletedIndices)
                                    {
                                        Console.WriteLine($"Deleted moe id:{_moes[i]}");
                                    }

                                    foreach (var i in changes.InsertedIndices)
                                    {
                                        Console.WriteLine($"Inserted moe id:{moes[i].Id} deviceId:{moes[i].DeviceId} name:{moes[i].MoeName} value:{moes[i].MoeValue}");
                                    }

                                    foreach (var i in changes.NewModifiedIndices)
                                    {
                                        Console.WriteLine($"Modified moe id:{moes[i].Id} deviceId:{moes[i].DeviceId} name:{moes[i].MoeName} value:{moes[i].MoeValue}");
                                    }

                                    if (changes.IsCleared)
                                    {
                                        Console.WriteLine("Collection cleared");
                                    }
                                    Console.ResetColor();
                                    await SaveMoesAsync();
                                }
                            }
                            catch (Exception ex)
                            {
                                ShowException(ex);
                            }
                        });

                    var options = new SubscriptionOptions
                    {
                        Name = CurrentUser.Id,
                        UpdateExisting = true
                    };

                    realm
                        .Subscriptions
                        .Add(myMoes, options);
                });

                realm.All<Moe>().AsRealmCollection().CollectionChanged += HandleCollectionChanged;
                if (realm.SyncSession.ConnectionState != ConnectionState.Disconnected)
                {
                    await realm.Subscriptions.WaitForSynchronizationAsync();
                };
                Console.WriteLine("Subscription created");
            }
            catch (Exception ex)
            {
                ShowException(ex);
            }
        }

            public async Task addManyMoesAsync()
            {
                var start = getInteger("starting index");
                var end = getInteger("ending index");
                for(var i = start; i <= end; i++) 
                {
                    var value = i.ToString();
                    await AddAsync(value, value, value);
                }
            } 

        public static async Task AddAsync(string deviceId, string moeName, string moeValue)
        {
            try
            {
                var realm = await GetMainThreadRealmAsync();
                await realm.WriteAsync(() =>
                {
                    realm.Add(new Moe()
                    {
                        WjaProxyId = CurrentUser.Id,
                        DeviceId = deviceId,
                        MoeName = moeName,
                        MoeValue = moeValue
                    });
                });
                Console.WriteLine("Moe added");
            }
            catch (Exception ex)
            {
                ShowException(ex);
            }
        }```

[finnschiermer]

Thanks for reporting this. A few initial questions:

0. is it possible to open/inspect the realm file after this error has been reported?
1. is this a local realm only scenario or is sync in use?
2. is the realm file encrypted or not?

[kiburtse]

@nicola-cab #6536 and #6531 might be relevant?

[nicola-cab]

@nicola-cab #6536 and #6531 might be relevant?

I am not sure @kiburtse, this seems a bad accessor being returned to the user in the notification (however I cannot exclude that this is somehow being generated by the same bug, but in core 13.4 there was no support for multiprocess encryption... which again could be just exposing the underlying bug more easily, which is what I suspect)

[jedelbo]

The issue here is that a block is being freed twice. The issues that @kiburtse refers to has the same symptom, so there is definitely something fishy here. @markstratman it sounds like you are able to reproduce this issue. Would it be possible to share a minimal application that can sometimes reproduce this? (I am not a .Net developer, so I am not able to figure out if the code above is sufficient)

[jedelbo]

Another duplicate of this could be #6340

[jedelbo]

@markstratman I would still like to pursue this issue. So it you still have a more complete program, that triggers this problem and if you are willing to share that, it would be most helpful.