Develop Reference

HttpClient throws httprequest exception on network restore

I am using System.Net.Http.HttpClient to make postaysnc request. While request is in progress I unplug the network cable, receive HttpRequestException.
After some time plug the network cable again and make the postasync request, getting the HttpRequestException - sometimes i get the response server not available,sometimes timeout
Do i need to dispose the httpclient on exception and recreate when the request is made? How to make the query successful on network restore.
private async Task<string> GetServerResult()
{
try
{
var response = await myHttpClient.PostAsync("https://google.com", httpContent);
response.EnsureSuccessStatusCode();
}
catch (HttpRequestException ex)
{
throw new HttpRequestException(ex.Message, ex.InnerException);
}
}

As per your requirement, you have to change implement some sort of implementation in that case. My proposed solution is use to a caching mechanism at WCF Client and update it periodically.
The very simple implementation could be as: You have a very simple singleton class of and a periodic Timer fetches the data from your mentioned endpoint. It stores the last cached data so that you have a copy of the data and when the hits are failed you can configure a fallback mechanism for that. For instance you have an implementation like
//You single Cache class
public sealed class ClientCache
{
#region Singleton implementation
private static ClientCache _clientCache = new ClientCache();
private ClientCache()
{
}
public static ClientCache Instance => _clientCache;
#endregion
//Timer for syncing the data from Server
private Timer _timer;
//This data is the cached one
public string data = string.Empty;
internal void StartProcess()
{
//Initializing the timer
_timer = new Timer(TimeSpan.FromMinutes(1).TotalMilliseconds); //This timespan is configurable
//Assigning it an elapsed time event
_timer.Elapsed += async (e, args) => await SyncServerData(e, args);
//Starting the timer
_timer.Start();
}
//In this method you will request your server and fetch the latest copy of the data
//In case of failure you can maintain the history of the last disconnected server
private async Task ProcessingMethod(object sender, ElapsedEventArgs e)
{
//First we will stop the timer so that any other hit don't come in the mean while
timer.Stop();
//Call your api here
//Once the hit is completed or failed
//On Success you will be updating the Data object
//data = result from your api call
//Finally start the time again as
timer.Start();
}
}
Now coming to Step two where to initialize the ClientCache Class. The best options are to initialize it in Global.asax class
protected void Application_Start()
{
//As
ClientCache.Instance.StartProcess();
}
Now whenever your frontend calls the method you don't need to go back to the server. Just send back the result from your cache as:
private Task<string> GetServerResult()
{
return Task.FromResult(ClientCache.Instance.data);
}

asp.net and multi threading and C# object

I'm new to ASP.net programming and I don't really understand the thing about multi threading . When I debug in my ASP.net app/website it shows a tab that I'm not familiar with: Parallel watch, it's something about multi threading. When I search about multi threading I only find examples about how to use multi-threading etc. The thing is, I'm not using any class for threading.
What I got in my code:
is my main page:
Index.aspx.cs:
protected void Button1_Click(object sender, EventArgs e)
{
string Message = PLC1.Connect();
lblClock.Text = Message;
}
and
protected void Timer1_Tick(object sender, EventArgs e)
{
if(PLC1.x_ConnectionEstablished)
{
string Message;
Message = PLC1.ReadDB(1, 0, 17);
if (Message == "OK")
{
lblClock.Text = "Connected and retrieved value!!";
}
else
{
lblClock.Text = Message;
}
}
else
{
lblClock.Text = "No connection! Press the button!";
}
}
my class: PLC.cs:
public string Connect()
{
int Result;
string Message;
Result = s7_S7Client.ConnectTo(s_IP, i_Rack, i_Slot);
Message = s7_S7Client.ErrorText(Result);
x_ConnectionEstablished = s7_S7Client.Connected();
return Message;
}
public string ReadDB(int a_DBnr, int a_startPos, int a_size)
{
int Result;
string Message = "";
try
{
Result = s7_S7Client.DBRead(a_DBnr, a_startPos, a_size, bArray_Buffer);
Message = s7_S7Client.ErrorText(Result);
}
catch (Exception E)
{
Message = E.Message;
}
return Message;
}
When I press the button (while debugging) it jumps to the Connect() of my PLC class. And it actually gives true on the x_ConnectionEstablished. But when my Timer triggers it doesn't go into my if-statement. Since it's saying: x_ConnectionEstablished = false.
I can add the code to the timer, but I don't want to execute the connection method each time I get in the timer(that's what I'm using this x_connectionEstablished for.
So my question is how does this threading work and how can I get my website running decently with or without the threading?

Your PLC1 and s7_S7Client appear to create some kind of persistent connection, for example through TCP sockets or a serial connection.
You don't want to create connections like this from an HTTP back-end, because HTTP is (or at least supposed to be) stateless: each request starts with a clean slate, all your variables (and thus connections) from the previous request are gone.
So I would advise wrapping this logic into a Windows Service that manages connecting to the PLC, and exposing the logic from this service through WCF.
Then your web application can issue requests, through WCF, to the service, and the service in turn talks to the PLC and maintains the connection.

Windows Service stuck on "starting" status as local system account

I developed a http server via console application in C# and decided to turn it into a Windows service to be able to initialize it without the need to login the machine.
I followed all the steps in How to create Windows Service and chose the account as "Local System", but when I install in my server machine and push the start button it takes a while and gives the following error:
Erro 1053: The service did not respond to the start or control request in timely fashion.
After that, the service status stays stuck in "starting" and the application don't work and I can't even stop the service anymore.
Trying to work around this problem, I changed it to "Network Service", so it started normally, but the application was not listening in the port I set when I checked in the prompt with the command "netstat -an". But the application listens normally if i run it as a console application.
So I am looking for an answer to one of these two questions:
What should I do to make the service starts properly with a Local System account?
If I decide to use Network service account, what should I care about to guarantee that my service works properly as a server?

When I converted my console application to windows service I simply put my code directly in the OnStart method. However, I realized the OnStart method should start the service, but needs to end some time to the service indeed start. So I created a thread that runs my service and let the OnStart method finish. I tested and the service worked just fine. Here is how it was the code:
protected override void OnStart(string[] args)
{
Listener(); // this method never returns
}
Here is how it worked:
protected override void OnStart(string[] args)
{
Thread t = new Thread(new ThreadStart(Listener));
t.Start();
}
But I still don't understand why the service ran (passed the "starting" status, but didn't work) when I used network service account. If anyone knows, I'll be glad to know the reason.

If you have a service that is not responding or showing pending in Windows services that you are unable to stop, use the following directions to force the service to stop.
Start -> Run or Start -> type services.msc and press Enter
Look for the service and check the Properties and identify its service name
Once found, open a command prompt. Type sc queryex [servicename]
Identify the PID (process ID)
In the same command prompt type taskkill /pid [pid number] /f

Find PID of Service
sc queryex <SERVICE_NAME>
Give result's below
SERVICE_NAME: Foo.Services.Bar TYPE : 10 WIN32_OWN_PROCESS STATE : 2 0 START_PENDING (NOT_STOPPABLE, NOT_PAUSABLE, IGNORES_SHUTDOWN) WIN32_EXIT_CODE : 0 (0x0) SERVICE_EXIT_CODE : 0 (0x0) CHECKPOINT : 0x0 WAIT_HINT : 0x0 PID : 3976 FLAGS :
Now Kill the Service:
taskkill /f /pid 3976
SUCESS: The process with PID 3976 has been terminated.

Check the Windows Application event log, it could contain some entries from your service's auto generated event source (which should have the same name of the service).

For me it was a while loop that looked at an external queue. The while-loop continued running until the queue was empty. Solved it by calling a timer event directly only when Environment.UserInteractive. Therefore the service could be debugged easily but when running as a service it would wait for the timers ElapsedEventHandler event.
Service:
partial class IntegrationService : ServiceBase
{
private static Logger logger = LogManager.GetCurrentClassLogger();
private System.Timers.Timer timer;
public IntegrationService()
{
InitializeComponent();
}
protected override void OnStart(string[] args)
{
try
{
// Add code here to start your service.
logger.Info($"Starting IntegrationService");
var updateIntervalString = ConfigurationManager.AppSettings["UpdateInterval"];
var updateInterval = 60000;
Int32.TryParse(updateIntervalString, out updateInterval);
var projectHost = ConfigurationManager.AppSettings["ProjectIntegrationServiceHost"];
var projectIntegrationApiService = new ProjectIntegrationApiService(new Uri(projectHost));
var projectDbContext = new ProjectDbContext();
var projectIntegrationService = new ProjectIntegrationService(projectIntegrationApiService, projectDbContext);
timer = new System.Timers.Timer();
timer.AutoReset = true;
var integrationProcessor = new IntegrationProcessor(updateInterval, projectIntegrationService, timer);
timer.Start();
}
catch (Exception e)
{
logger.Fatal(e);
}
}
protected override void OnStop()
{
try
{
// Add code here to perform any tear-down necessary to stop your service.
timer.Enabled = false;
timer.Dispose();
timer = null;
}
catch (Exception e)
{
logger.Fatal(e);
}
}
}
Processor:
public class IntegrationProcessor
{
private static Logger _logger = LogManager.GetCurrentClassLogger();
private static volatile bool _workerIsRunning;
private int _updateInterval;
private ProjectIntegrationService _projectIntegrationService;
public IntegrationProcessor(int updateInterval, ProjectIntegrationService projectIntegrationService, Timer timer)
{
_updateInterval = updateInterval;
_projectIntegrationService = projectIntegrationService;
timer.Elapsed += new ElapsedEventHandler(OnTimedEvent);
timer.Interval = _updateInterval;
//Don't wait for first elapsed time - Should not be used when running as a service due to that Starting will hang up until the queue is empty
if (Environment.UserInteractive)
{
OnTimedEvent(null, null);
}
_workerIsRunning = false;
}
private void OnTimedEvent(object source, ElapsedEventArgs e)
{
try
{
if (_workerIsRunning == false)
{
_workerIsRunning = true;
ProjectInformationToGet infoToGet = null;
_logger.Info($"Started looking for information to get");
//Run until queue is empty
while ((infoToGet = _projectIntegrationService.GetInformationToGet()) != null)
{
//Set debugger on logger below to control how many cycles the service should run while debugging.
var watch = System.Diagnostics.Stopwatch.StartNew();
_logger.Info($"Started Stopwatch");
_logger.Info($"Found new information, updating values");
_projectIntegrationService.AddOrUpdateNewInformation(infoToGet);
_logger.Info($"Completed updating values");
watch.Stop();
_logger.Info($"Stopwatch stopped. Elapsed seconds: {watch.ElapsedMilliseconds / 1000}. " +
$"Name queue items: {infoToGet.NameQueueItems.Count} " +
$"Case queue items: {infoToGet.CaseQueueItems.Count} " +
$"Fee calculation queue items: {infoToGet.FeeCalculationQueueItems.Count} " +
$"Updated foreign keys: {infoToGet.ShouldUpdateKeys}");
}
_logger.Info($"Nothing more to get from integration service right now");
_workerIsRunning = false;
}
else
{
_logger.Info($"Worker is already running! Will check back again after {_updateInterval / 1000} seconds");
}
}
catch (DbEntityValidationException exception)
{
var newException = new FormattedDbEntityValidationException(exception);
HandelException(newException);
throw newException;
}
catch (Exception exception)
{
HandelException(exception);
//If an exception occurs when running as a service, the service will restart and run again
if (Environment.UserInteractive)
{
throw;
}
}
}
private void HandelException(Exception exception)
{
_logger.Fatal(exception);
_workerIsRunning = false;
}
}

You can try to increase the windows service timeout with a key in the registry
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control
"ServicesPipeTimeout"=dword:300000 (300 seconds or 5 minutes)
If it doesn't exists it has to be created.

How to make windows service request wait until the previous request is complete

I am working on a window services application and my window service will call one of the web services in certain intervals (for example 3 min). From the web service I will get data from a database and using that data I will send an email.
If I am having huge sets of rows in my db table it will take some time to send the mail. Here I have the problem: The window services send the first request and it will handle some set of records. So, while processing it by the web service, the window service sends another request to the web service before it has completed the first request.
Due to this, the web service gets the same records from db again and again whenever it receives a new request from the windows service.
Can any one suggest me how to lock the previous request until it completes its work or some other way to handle this situation?
Web Service call:
protected override void OnStart(string[] args)
{
timer.Elapsed += new ElapsedEventHandler(OnElapsedTime);
timer.Interval = 180000;
timer.AutoReset = false;
timer.Enabled = true;
}
Inside Method
using (MailWebService call = new MailWebService())
{
try
{
call.ServiceUrl = GetWebServiceUrl();
System.Net.ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };
call.CheckMailQueue();
}
catch (Exception ex)
{
LogHelper.LogWriter(ex);
}
finally
{
}
}

The Monitor class works great for this scenario. Here is an example of how to use it:
// This is the object that we lock to control access
private static object _intervalSync = new object();
private void OnElapsedTime(object sender, ElapsedEventArgs e)
{
if (System.Threading.Monitor.TryEnter(_intervalSync))
{
try
{
// Your code here
}
finally
{
// Make sure Exit is always called
System.Threading.Monitor.Exit(_intervalSync);
}
}
else
{
//Previous interval is still in progress.
}
}
There is also an overload for TryEnter that allows you to specify timeout for entering the section.

XSockets Client Connecting But Not Receiving Messages

I'm trying to set up a specific scenario but, obviously, I'm having problems. My server is a site that primarily hosts a WCF service but I want to add an XSockets host there as well. I have the standard code in the bootstrap code file as per the instructions in the readme.txt. Upon a client connection, I am starting a worker thread which is basically a heartbeat that the client will monitor. The relevant code from the controller is as follows:
public class HeartbeatController : XSocketController
{
public void AddMessage(string message)
{
this.SendToAll(message, "addMessage");
}
}
Within my worker thread I am calling this:
string message = String.Format("pump", Math.Round(cpuCounter.NextValue());
ClientPool connection = ClientPool.GetInstance("ws://mywebsite:4502/HeartbeatController", "*");
connection.Send(message, "addMessage");
Currently I'm testing this with a console client which looks like this:
class Program
{
static XSocketClient socketClient;
static void Main(string[] args)
{
Console.WriteLine("Starting client...");
string url = "ws://mywebsite:4502/HeartbeatController";
socketClient = new XSocketClient(url, "*");
socketClient.OnOpen += socketClient_OnOpen;
socketClient.Open();
while (true)
{
// let it sit and display the "pump" messages
string input = Console.ReadLine();
if (input.Equals("Q", StringComparison.Ordinal))
{
break;
}
}
}
static void socketClient_OnOpen(object sender, EventArgs e)
{
Console.WriteLine("socketClient Opened");
socketClient.Bind("addMessage", OnAddMessage);
}
private static void OnAddMessage(ITextArgs textArgs)
{
Console.WriteLine("AddMessage :: {0}", textArgs.data);
}
}
On the client, if I put a breakpoint in the socketClient_OnOpen method it gets hit so I think it is connecting. But the pump message never makes it to the client.
Two Questions:
Is there anything obvious that I'm missing?
(Unrelated) Since many enterprises really don't like punching holes in their firewalls, is there any way to use port 80 with this setup (so that the client connection would look like "ws://mywebsite/HeartbeatController")?
Thanks for any help!

So to see what your pump actually was sending in to the server I added a custom pipeline.
public class MyPipeline : XSocketPipeline
{
//Incomming textmessage
public override void OnMessage(IXSocketController controller, ITextArgs e)
{
Console.WriteLine("IN " + e.data);
//Let the message continue into the server
base.OnMessage(controller, e);
}
//Outgoing textmessage
public override ITextArgs OnSend(IXSocketProtocol protocol, ITextArgs e)
{
Console.WriteLine("OUT " + e.data);
return base.OnSend(protocol, e);
}
}
Since I then saw that you was sending in a string that actually did not have a property named "message". The actionmethod "AddMessage" expects you to pass in a property message of type string. So you can solve this in two ways, both of them are simple.
Just replace the string parameter in the AddMessage with ITextArgs
public void AddMessage(ITextArgs message)
or...
Pass in a object from your worker thread instead of a string like this
connection.Send(new {message}, "addMessage");
So all you need to do to get it to work is to change this row
connection.Send(message, "addMessage");
with this row
connection.Send(new {message}, "addMessage");
EDIT: Btw, 4.0 is on the way and the client will be very much improved as well as the serverside stuff.