JsonConvert.DeserializeObject and ThreadAbortedException

Question

In Xamarin project I have PCL library with the following code.

We define a ConcurrentQueue<SyncRequest>. For which on object initialization the consumer Task has been attached:

_syncConsumer = new Task(
                ProcessSyncQueue,
                _syncConsumerCancellationTokenSource.Token);
_syncConsumer.Start();

The ProcessSyncQueue method scans synchronization queue and call GetSyncableEntity method:

private async void ProcessSyncQueue()
{
    while (true)
    {
         SyncRequest syncRequest;
         if (_syncQueue.TryDequeue(out syncRequest))
         {
             var syncableEntity = GetSyncableEntity(syncRequest);
         }
    }
}

GetSyncableEntity in turn performs Json deserialization:

private T GetSyncableEntity(SyncRequest syncRequest)
{
    T syncableEntity = default(T);

    try
    {
       syncableEntity = JsonConvert.DeserializeObject<T>(syncRequest.SynchronizationContent);
    }
    catch (Exception e)
    {

    }

    return syncableEntity;
 }

On this step we receive ThreadAbortedException with 'Thread was being aborted' message. Stacktrace:

   at Newtonsoft.Json.JsonTextReader.FinishReadStringIntoBuffer(Int32 charPos, Int32 initialPosition, Int32 lastWritePosition)
   at Newtonsoft.Json.JsonTextReader.ReadStringIntoBuffer(Char quote)
   at Newtonsoft.Json.JsonTextReader.ParseProperty()
   at Newtonsoft.Json.JsonTextReader.ParseObject()
   at Newtonsoft.Json.JsonTextReader.Read()
   at Newtonsoft.Json.JsonReader.ReadAndAssert()
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
   at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
   at Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonSerializerSettings settings)
   at Newtonsoft.Json.JsonConvert.DeserializeObject[T](String value, JsonSerializerSettings settings)
   at Newtonsoft.Json.JsonConvert.DeserializeObject[T](String value)

Can anyone help us to understand what is going on and how it should be deserialized?

UPDATE: I post a bit more code, as reviewers suggested I deleted CancellationTokenSource, use Task.Run to initialize consumer and await it. And created some test implementation like this:

    protected void RequestSynchronizationFor(
        string synchronizationKey,
        T entity)
    {
        if (!_isInitialized)
        {
            InitializeSyncRequestsQueue();
        }

        _syncQueue.Enqueue(GetSyncRequest(synchronizationKey, entity));
    }

So we request entity to be synchronized calling RequestSynchronizationFor method. If it is cold run we initialize the queue from db calling InitializeSyncRequestsQueue and await Task.Run consumer thread.

    private async void InitializeSyncRequestsQueue()
    {
        var syncRequests = GetSyncedRequests();

        foreach (var syncRequest in syncRequests)
        {
            _syncQueue.Enqueue(syncRequest);
        }

        await Task.Run(ProcessSyncQueue);
    }

Consumer task as before does the same things:

 private async Task ProcessSyncQueue()
    {
        while (true)
        {
            SyncRequest syncRequest;
            if (_syncQueue.TryDequeue(out syncRequest))
            {
                var syncableEntity = GetSyncableEntity(syncRequest);
            }
        }
    }

Still got the same exception. Not sure if it is sensible, but I am running the code from the unit-test. Any suggestions?

UPDATE2:

After I did changes I posted in first 'UPDATE', the call stack was changed a bit as well:

   at Newtonsoft.Json.JsonSerializer.get_MetadataPropertyHandling()
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
   at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
   at Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonSerializerSettings settings)
   at Newtonsoft.Json.JsonConvert.DeserializeObject[T](String value, JsonSerializerSettings settings)
   at Newtonsoft.Json.JsonConvert.DeserializeObject[T](String value)

UPDATE 3: I extract all the code in fake service and still have the same exception, while trying to deserialize:

public class JsonDeserializeService<T>
{
    private readonly bool _isInitialized;

    private readonly ConcurrentQueue<SyncRequest> _syncQueue;

    public JsonDeserializeService()
    {
        _isInitialized = false;
        _syncQueue = new ConcurrentQueue<SyncRequest>();
    }

    public void RequestSynchronizationFor(
        string synchronizationKey,
        T entity)
    {
        if (!_isInitialized)
        {
            InitializeSyncRequestsQueue();
        }

        _syncQueue.Enqueue(GetSyncRequest(synchronizationKey, entity));
    }

    private async void InitializeSyncRequestsQueue()
    {
        var syncRequests = Enumerable.Empty<SyncRequest>();

        foreach (var syncRequest in syncRequests)
        {
            _syncQueue.Enqueue(syncRequest);
        }

        await Task.Run(ProcessSyncQueue);
    }

    private async Task ProcessSyncQueue()
    {
        while (true)
        {
            SyncRequest syncRequest;
            if (_syncQueue.TryDequeue(out syncRequest))
            {
                var syncableEntity = GetSyncableEntity(syncRequest);
            }
        }
    }

    private T GetSyncableEntity(SyncRequest syncRequest)
    {
        T syncableEntity = default(T);

        try
        {
            syncableEntity = JsonConvert.DeserializeObject<T>(syncRequest.SynchronizationContent);
        }
        catch (Exception e)
        {
        }

        return syncableEntity;
    }

    private SyncRequest GetSyncRequest(string synchronizationKey, T entity)
    {
        return new SyncRequest()
        {
            SynchronizationContent = JsonConvert.SerializeObject(entity),
            SynchronizationDelayUntil = DateTime.Now
        };
    }
}

Triggered from unit-test:

    public void Syncable_Service_Should_Not_Generate_Exception()
    {
        var syncService = new JsonDeserializeService<FakeSyncableEntity>();
        syncService.RequestSynchronizationFor("syncKey", new FakeSyncableEntity() { Content = "Content" });
    }

Answer 1

The reason for this behavior is very simple. Your test ends ealier than the async task. When test ends it raises ThreadAbortException for child threads.

You need to call task.Wait() to make main thread wait for task completion.