Develop Reference

gRPC with WPF not working

I am trying to get the gRPC C# example working inside WPF.
The same code which is working inside a Console Application is not working. What am I missing.
The minimal class which works in the Console App and does not work in WPF looks like this:
public class GrpcClientImpl
{
private GrpcService.GrpcService.GrpcServiceClient client;
public GrpcTestClientImpl()
{
var channel = new Channel("127.0.0.1:6980", ChannelCredentials.Insecure);
client = new GrpcService.GrpcService.GrpcServiceClient(channel);
ProcessFeed().Wait();
}
public async Task ProcessFeed()
{
try
{
using (var call = client.Feed(new FeedRequest()))
{
var responseStream = call.ResponseStream;
while (await responseStream.MoveNext())
{
var result = responseStream.Current;
Console.WriteLine("received result");
}
}
}
catch (RpcException e)
{
Console.WriteLine("RPC failed " + e);
throw;
}
}
}
The responseStream.MoveNext() is where it is hanging. It does not respond to sent items and it does also not trigger an exception if the gRPC server is not there. What have I missed?

The problem is the blocking call ProcessFeed().Wait(); within the constructor.
This post explains why:
http://blog.stephencleary.com/2012/07/dont-block-on-async-code.html
To solve the issue, call await ProcessFeed(); from outside (not in the costructor).

Pusher for Windows Phone failing to disconnect

I have encountered a problem with pusherClient.wp8 package I installed from Nuget. Every time the app is sent to the background, I disconnect from pusher and unsubscribe from the channel. when I resume the app, the code hang when connection is re-established with pusher.
I have tried to reset the pusher object, reset the channel, create a new instance of pusher, and still nothing works, it seems there is a problem with the package, or rather the websocket disconnect method is failing to disconnect from pusher, however, when I close the app, everything get reseted. but this does not help me in instances when a user open a photopicker from my app.
Does anyone has a suggestion or know of another pusherclient I can use for windows phone 8. I have been struggling with this problem for weeks now.
Here is the github link of the package I used: https://github.com/bszypelow/PusherClient.WP8/blob/master/PusherClient.WP8
Thank you
public ConnectionState Connect()
{
var task = Task.Run(async () => await pusher.ConnectAsync()); ;
try
{
task.Wait();
}
catch (Exception ex)
{
Debug.WriteLine("Exception " + ex.Message + " at " + ex.Source + "Inner exception " + ex.InnerException + " additional data " + ex.Data);
}
return task.Result;
}

From looking at the source code I have a guess:
All the async methods never use .ConfigureAwait(false) which could be a reason for the dead lock.
Especially if you call it from the UI thread using the .Wait() or .Result. From event for example.
I suggest you to update the code (it's MIT license, you can do that):
public Task<Channel> Subscribe(string channelName)
{
if (_connection.State != ConnectionState.Connected)
throw new PusherException("You must wait for Pusher to connect before you can subscribe to a channel", ErrorCodes.NotConnected);
if (Channels.ContainsKey(channelName))
{
return Task.FromResult(Channels[channelName]);
}
// If private or presence channel, check that auth endpoint has been set
var chanType = ChannelTypes.Public;
if (channelName.ToLower().StartsWith("private-"))
chanType = ChannelTypes.Private;
else if (channelName.ToLower().StartsWith("presence-"))
chanType = ChannelTypes.Presence;
return SubscribeToChannel(chanType, channelName); //await is not needed here
}
private async Task<Channel> SubscribeToChannel(ChannelTypes type, string channelName)
{
switch (type)
{
case ChannelTypes.Public:
Channels.Add(channelName, new Channel(channelName, this));
break;
case ChannelTypes.Private:
AuthEndpointCheck();
Channels.Add(channelName, new PrivateChannel(channelName, this));
break;
case ChannelTypes.Presence:
AuthEndpointCheck();
Channels.Add(channelName, new PresenceChannel(channelName, this));
break;
}
if (type == ChannelTypes.Presence || type == ChannelTypes.Private)
{
string jsonAuth = await _options.Authorizer.Authorize(channelName, _connection.SocketID)
.ConfigureAwait(false); //do not capture the context!!
var template = new { auth = String.Empty, channel_data = String.Empty };
var message = JsonConvert.DeserializeAnonymousType(jsonAuth, template);
_connection.Send(JsonConvert.SerializeObject(new { #event = Constants.CHANNEL_SUBSCRIBE, data = new { channel = channelName, auth = message.auth, channel_data = message.channel_data } }));
}
else
{
// No need for auth details. Just send subscribe event
_connection.Send(JsonConvert.SerializeObject(new { #event = Constants.CHANNEL_SUBSCRIBE, data = new { channel = channelName } }));
}
return Channels[channelName];
}
You can checkout the source code, than if you don't use it now you can install trial version of ReSharper and this plug-in. They will help you to find all the lines where .ConfigureAwait is missing.

limit # of web service requests simultaneously

I have an Excel Add-In written in C#, .NET 4.5. It will send many web service requests to a web server to get data. E.g. it sends 30,000 requests to web service server. When data of a request comes back, the addin will plot the data in Excel.
Originally I did all the requests asynchronously, but sometime I will get OutOfMemoryException
So I changed, sent the requests one by one, but it is too slow, takes long time to finish all requests.
I wonder if there is a way that I can do 100 requests at a time asynchronously, once the data of all the 100 requests come back and plot in Excel, then send the next 100 requests.
Thanks
Edit
On my addin, there is a ribbon button "Refresh", when it is clicked, refresh process starts.
On main UI thread, ribbon/button is clicked, it will call web service BuildMetaData,
once it is returned back, in its callback MetaDataCompleteCallback, another web service call is sent
Once it is returned back, in its callback DataRequestJobFinished, it will call plot to plot data on Excel. see below
RefreshBtn_Click()
{
if (cells == null) return;
Range firstOccurence = null;
firstOccurence = cells.Find(functionPattern, null,
null, null,
XlSearchOrder.xlByRows,
XlSearchDirection.xlNext,
null, null, null);
DataRequest request = null;
_reportObj = null;
Range currentOccurence = null;
while (!Helper.RefreshCancelled)
{
if(firstOccurence == null ||IsRangeEqual(firstOccurence, currentOccurence)) break;
found = true;
currentOccurence = cells.FindNext(currentOccurence ?? firstOccurence);
try
{
var excelFormulaCell = new ExcelFormulaCell(currentOccurence);
if (excelFormulaCell.HasValidFormulaCell)
{
request = new DataRequest(_unityContainer, XLApp, excelFormulaCell);
request.IsRefreshClicked = true;
request.Workbook = Workbook;
request.Worksheets = Worksheets;
_reportObj = new ReportBuilder(_unityContainer, XLApp, request, index, false);
_reportObj.ParseParameters();
_reportObj.GenerateReport();
//this is necessary b/c error message is wrapped in valid object DataResponse
//if (!string.IsNullOrEmpty(_reportObj.ErrorMessage)) //Clear previous error message
{
ErrorMessage = _reportObj.ErrorMessage;
Errors.Add(ErrorMessage);
AddCommentToCell(_reportObj);
Errors.Remove(ErrorMessage);
}
}
}
catch (Exception ex)
{
ErrorMessage = ex.Message;
Errors.Add(ErrorMessage);
_reportObj.ErrorMessage = ErrorMessage;
AddCommentToCell(_reportObj);
Errors.Remove(ErrorMessage);
Helper.LogError(ex);
}
}
}
on Class to GenerateReport
public void GenerateReport()
{
Request.ParseFunction();
Request.MetacompleteCallBack = MetaDataCompleteCallback;
Request.BuildMetaData();
}
public void MetaDataCompleteCallback(int id)
{
try
{
if (Request.IsRequestCancelled)
{
Request.FormulaCell.Dispose();
return;
}
ErrorMessage = Request.ErrorMessage;
if (string.IsNullOrEmpty(Request.ErrorMessage))
{
_queryJob = new DataQueryJob(UnityContainer, Request.BuildQueryString(), DataRequestJobFinished, Request);
}
else
{
ModifyCommentOnFormulaCellPublishRefreshEvent();
}
}
catch (Exception ex)
{
ErrorMessage = ex.Message;
ModifyCommentOnFormulaCellPublishRefreshEvent();
}
finally
{
Request.MetacompleteCallBack = null;
}
}
public void DataRequestJobFinished(DataRequestResponse response)
{
Dispatcher.Invoke(new Action<DataRequestResponse>(DataRequestJobFinishedUI), response);
}
public void DataRequestJobFinished(DataRequestResponse response)
{
try
{
if (Request.IsRequestCancelled)
{
return;
}
if (response.status != Status.COMPLETE)
{
ErrorMessage = ManipulateStatusMsg(response);
}
else // COMPLETE
{
var tmpReq = Request as DataRequest;
if (tmpReq == null) return;
new VerticalTemplate(tmpReq, response).Plot();
}
}
catch (Exception e)
{
ErrorMessage = e.Message;
Helper.LogError(e);
}
finally
{
//if (token != null)
// this.UnityContainer.Resolve<IEventAggregator>().GetEvent<DataQueryJobComplete>().Unsubscribe(token);
ModifyCommentOnFormulaCellPublishRefreshEvent();
Request.FormulaCell.Dispose();
}
}
on plot class
public void Plot()
{
...
attributeRange.Value2 = headerArray;
DataRange.Value2 = ....
DataRange.NumberFormat = ...
}

OutOfMemoryException is not about the too many requests sent simultaneously. It is about freeing your resources right way. In my practice there are two main problems when you are getting such exception:
Wrong working with immutable structures or System.String class
Not disposing your disposable resources, especially graphic objects and WCF requests.
In case of reporting, for my opinion, you got a second one type of a problem. DataRequest and DataRequestResponse are good point to start the investigation for the such objects.
If this doesn't help, try to use the Tasks library with async/await pattern, you can find good examples here:
// Signature specifies Task<TResult>
async Task<int> TaskOfTResult_MethodAsync()
{
int hours;
// . . .
// Return statement specifies an integer result.
return hours;
}
// Calls to TaskOfTResult_MethodAsync
Task<int> returnedTaskTResult = TaskOfTResult_MethodAsync();
int intResult = await returnedTaskTResult;
// or, in a single statement
int intResult = await TaskOfTResult_MethodAsync();
// Signature specifies Task
async Task Task_MethodAsync()
{
// . . .
// The method has no return statement.
}
// Calls to Task_MethodAsync
Task returnedTask = Task_MethodAsync();
await returnedTask;
// or, in a single statement
await Task_MethodAsync();
In your code I see a while loop, in which you can store your Task[] of size of 100, for which you can use the WaitAll method, and the problem should be solved. Sorry, but your code is huge enough, and I can't provide you a more straight example.

I'm having a lot of trouble parsing your code to figure out is being iterated for your request but the basic template for batching asynchronously is going to be something like this:
static const int batchSize = 100;
public async Task<IEnumerable<Results>> GetDataInBatches(IEnumerable<RequestParameters> parameters) {
if(!parameters.Any())
return Enumerable.Empty<Result>();
var batchResults = await Task.WhenAll(parameters.Take(batchSize).Select(doQuery));
return batchResults.Concat(await GetDataInBatches(parameters.Skip(batchSize));
}
where doQuery is something with the signature
Task<Results> async doQuery(RequestParameters parameters) {
//.. however you do the query
}
I wouldn't use this for a million requests since its recursive, but your case should would generate a callstack only 300 deep so you'll be fine.
Note that this also assumes that your data request stuff is done asynchronously and returns a Task. Most libraries have been updated to do this (look for methods with the Async suffix). If it doesn't expose that api you might want to create a separate question for how to specifically get your library to play nice with the TPL.

Xamarin Forms - WCF completed event not changing components

Currently i'm working on a Xamarin.Forms application with WCF. The app makes a connection to the WCF host and I get a response back, only I can't do anything with the results of the response.
My code of the method that's supposed to take care of the response is:
private static void ClientOnGetHelloDataCompleted(object sender, GetHelloDataCompletedEventsArgs getHelloDataCompletedEventArgs)
{
string msg = null;
if(getHelloDataCompletedEventArgs.Error != null)
{
msg = getHelloDataCompletedEventArgs.Error.Message;
}
else if(getHelloDataCompletedEventArgs.Cancelled != null)
{
msg = "Request was cancelled";
}
else
{
lblText.Text = getHelloDataCompletedEventArgs.Results.Name;
}
}
When I debug I can see Results.Name is filled, but for some reason it doesn't update the label named lblText.
This method is placed in de App.cs (Xamarin Forms portable project).
Anyone here that can help me with this problem?

you should refresh the U.I in the main thread, here is the fix
else
{
InvokeOnMainThread(() => lblText.Text = getHelloDataCompletedEventArgs.Results.Name);
}

Best way to handle a WCF timeout

I have a real time app that tracks assets around a number of sites across the country. As part of this solution I have 8 client apps that update a central server.
My question is that sometimes the apps lose connection to the central server and I am wondering what is the best way to deal with this ? I know I could just increase the max send/receive times to deal with the timeout BUT I also want a graceful solution to deal with if the connection to the server is down:
For example I'm calling my services like this :
using (var statusRepository = new StatusRepositoryClient.StatusRepositoryClient())
{
statusId = statusRepository.GetIdByName(licencePlateSeen.CameraId.ToString());
}
I was thinking of adding a try/catch so...
using (var statusRepository = new StatusRepositoryClient.StatusRepositoryClient())
{
try
{
statusId = statusRepository.GetIdByName(licencePlateSeen.CameraId.ToString());
}
catch (TimeoutException timeout)
{
LogMessage(timeout);
}
catch (CommunicationException comm)
{
LogMessage(comm);
}
}
Dealing it this way doesn't allow me to rerun the code without having a ton of code repeat. Any one got any suggestions ?
EDIT: Looking into Sixto Saez and user24601 answers having an overall solution is better than dealing with timeouts on an individual exception level BUT... I'm was thinking that the below would solve my problem (but it would add a TON of extra code error handling):
void Method(int statusId)
{
var statusRepository = new StatusRepositoryClient.StatusRepositoryClient()
try
{
IsServerUp();
statusId = statusRepository.GetIdByName(licencePlateSeen.CameraId.ToString());
statusRepository.Close();
}
catch (Exception ex)
{
statusRepository.Abort();
if (ex is TimeoutException || ex is CommunicationException)
{
LogMessage(timeout);
Method(statusId);
}
else
{
throw new Exception(ex.Message + ex.InnerException);
}
}
}
}
bool IsServerUp()
{
var x = new Ping();
var reply = x.Send(IPAddress.Parse("127.0.0.1"));
if (reply == null)
{
IsServerUp();
}
else
{
if (reply.Status != IPStatus.Success)
{
IsServerUp();
}
}
return true;
}

For starters I think your Wcf error handling is wrong. It should look like this
var statusRepository = new StatusRepositoryClient.StatusRepositoryClient();
try
{
statusId = statusRepository.GetIdByName(licencePlateSeen.CameraId.ToString());
statusRepository.Close()
}
catch(Exception e)
{
statusRepository.Abort();
LogMessage(e);
throw; //I would do this to let user know.
}
I would also re-throw the error to let the user know about the problem.

Prior to designing your exception handling, one important decision to make is whether you want guaranteed delivery of each message the client sends or is it OK for the service to "lose" some. For guaranteed delivery, the best built-in solution is the netMsmqBinding assuming the client can be configured to support it. Otherwise, there is a lightweight reliable messaging capability built into WCF. You'll be going down a rabbit hole if you try to handle message delivery purely through exception handling... :)

I have a two-pronged approach to verifying the server is up:
1) I have set up a 'PING' to the server every 5 seconds. The server responds with a 'PONG' and a load rating (low, medium, high, so the client can adjust its load on the server). If the client EVER doesn't receive a pong it assumes the server is down (since this is very low stress on the server - just listen and respond).
2) Random timeouts like the one you are catching are logged in a ConnectionMonitor class along with all successful connections. A single one of these calls timing out is not enough to consider the server down since some may be very processor heavy, or may just take a very long time. However, a high enough percentage of these will cause the application to go into server timeout.
I also didn't want to throw up a message for every single connection timeout, because it was happening too frequently to people who use poorer servers (or just some computer lying in their lab as a server). Most of my calls can be missed once or twice, but missing 5 or 6 calls are clearly going to cause instrusion.
When a server-timeout state happens, I throw up a little dialog box explaining what's happening to the user.

Hi Please see my solution below. Also please note that the below code has not been compliled so may have some logic and typing errors.
bool IsServerUp()
{
var x = new Ping();
var reply = x.Send(IPAddress.Parse("127.0.0.1"));
if (reply == null) return false;
return reply.Status == IPStatus.Success ? true : false;
}
int? GetStatusId()
{
try
{
using (var statusRepository = new StatusRepositoryClient.StatusRepositoryClient())
{
return statusRepository.GetIdByName(licencePlateSeen.CameraId.ToString());
}
}catch(TimeoutException te)
{
//Log TimeOutException occured
return null;
}
}
void GetStatus()
{
try
{
TimeSpan sleepTime = new TimeSpan(0,0,5);
int maxRetries = 10;
while(!IsServerUp())
{
System.Threading.Thead.Sleep(sleepTime);
}
int? statusId = null;
int retryCount = 0;
while (!statusId.HasValue)
{
statusId = GetStatusId();
retryCount++;
if (retryCount > maxRetries)
throw new ApplicationException(String.Format("{0} Maximum Retries reached in order to get StatusId", maxRetries));
System.Threading.Thead.Sleep(sleepTime);
}
}catch(Exception ex)
{
//Log Exception Occured
}
}