I have been experiencing a problem with one of my vb applications where it is crashing at a certain time of day. In my code, there are only 4 places where that could be the cause of the crash. Three of them are from SQLDataSource queries and the other is in the code behind. I am pretty sure that I don't have a problem with the code behind as I have a using block in place. Further more, inside of that block I have a try catch finally where in the finally I am Disposing the command as well as the connection and Closing the connection. I have been reading some articles that tell me that I should use a SqlDataSource "selected" event to close the connection. I gave that a try but didn't have any success. This is the error that I am receiving:
SqlException (0x80131904): Execution Timeout Expired. The timeout period elapsed prior to completion of the operation or the server is not responding.
This makes me feel like the "selected" event is not having a chance to get fired. So I thought I should try the "selecting" event. In it, I am trying to grab the connection string and close it. But I am not quite sure I am going down the correct path because I have been unable to catch exceptions inside of that event. Can someone out there please give me a hand with this issue I am facing?
Edit:
This is an example of how I am trying to use the selected event to close the connection
If Not IsNothing(e.Exception) Then
Debug.Print("Exeception encounted while selecting for sqlData")
End If
e.ExceptionHandled = True
And here is and example of how I am trying to use the selecting event (I cannot figure out if an exception has been thrown here).
Dim sqlDataConn As SqlConnection = New SqlConnection("MYConnectionString")
sqlDataConn.Dispose()
If you want to intercept SqlException you need to use explicit "using", i.e. try/catch. Then, you can determine specific issue by the Number property.
try
catch ex as SqlException
MessageBox.Show(ex.Number)
if ex.Number = xxx then
' do something
end if
catch ex as Exception
finally
end try
if the question about handling this
If Not IsNothing(e.Exception) Then
Debug.Print("Exeception encounted while selecting for sqlData")
End If
you can check the exception type
If e.Exception IsNot Nothing AndAlso TypeOf e.Exception Is SqlException Then
.....
It would help if you did a breakpoint and found the query that was having this issue. The timeout issue is when a long-running query kills itself because it ran past the default timeout period.
A quick and dirty solution could be to just use a larger timeout in the connection strings you use, but long running queries can usually be a bad sign of an unoptimized query and should be addressed before your database grows any larger.
Related
I have a simple Try Catch function like:
Try
'do that
Catch
'didn't work now try again
End Try
Now I want the Error / Catch Message to be displayed as Messagebox which works with:
Catch ex As Exception
Messagebox.Show(ex.message)
The issue with that is that it always Stops / Quits the Application after showing me the Error Message which I want to prevent. This should try something until it works and always display the error message without stopping. Is that possible? I need it as compiled exe so just Debugging won't be an option.
As Explanation what I am trying to do:
Basically I have a Timer that executes every 10 Seconds a Request to my Server. It check if my Server is up and connected. If it can't reach my Server it should exactly display me the Message why it didn't connect but it shouldn't stop, it should continue pinging my server 10 seconds later again and try again until it works. The thing is that the exception message sometimes changes so I really need the Exception Message as output
It sounds like right now you have a method that sometimes throws like this:
Public Sub CheckServer()
' do something to test the server
End Function
If the code is not isolated to it's own method like that, it should be.
And you want to call it like this:
Try
CheckServer()
Catch ex As Exception
MessageBox.Show(...)
End Try
I suggest moving the Try/Catch inside the method and making it return a value:
Public Function CheckServer() As String
Try
' do something to test the server
Catch ex As Exception
Return ex.Message
End Try
Return String.Empty
End Function
And then call it like this:
Dim errorMessage As String = CheckServer()
If Not String.IsNullOrEmpty(errorMessage) Then
SendAlert(errorMessage)
End If
Where you also have a separate alert method:
Public Sub SendAlert(alertText As String)
SomeControl.Text += $"{Now} -- {alertText}{vbCrLf}"
End Sub
Notice I did not use MessageBox, because it blocks your UI. But the idea here is this makes it easy to change what you want to do with the alerts when they come in. For example, you might create a toast notification.
Since you're using WinForms, the other thing you could do here is define and then raise an event, rather than returning a value.
Are you using TCPClient to connect ??? If you are, you can just write an IsConnected code. TCP client stays connected until the server or client go out.
The most common error message when a server is not accepting connections is the “server did not properly respond in time message”
Constantly sending the server a request isn’t ideal. You need a one notification to come through when the connection is lost... and then set the timer to constantly try to reconnect.
I like VB.Net, but there is something that is driving me nuts. Too many times when an exception occurs, it simply continues somewhere else, usually by exiting the sub or function, but otherwise keeps on rolling. As an example, I was using Asc() instead of AscW(). It didn't throw an exception, it just left the function as if a Return was executed. Meanwhile I'm leaving red dot stop points all over like it has chicken pox trying to figure out what is causing it.
Is there a setting that can be used to used to actually cause VB to stop and give a line number?
Try catch statements will help you out greatly.
Take a read here: https://msdn.microsoft.com/en-us/library/fk6t46tz.aspx
Have you tried using a Try..Catch..Finally statement. E.g. The ex.string will put the exception into a string in the message and tell you the vb line.
Try
'code here
Catch ex as Exception
MessageBox.Show("Something went wrong. " & ex.ToString, "Data Error ")
End Try
Checking on a best practice here.
I am calling a ThreadPool to run an Async process, specifically sending an SSL email with an attachment which seems to take a good long while.
This is just test code, I thought I would drop this in a Try Catch just incase something failed. But will the thread ever even come back here? I have tested this closing the web page, the browser, clicking the back button on the page. The email always makes it through.
Try
System.Threading.ThreadPool.QueueUserWorkItem(AddressOf DoAsyncWork) '
Catch ex As Exception
Throw ex
Exit Sub
End Try
I am not trying to force a failure, yet I guess, but I would like to know how best to trap if the thread fails.
Protected Sub DoAsyncWork(ByVal state As Object)
Dim oMyObject As New sendSSLemail
oMyObject.SSL(userName, , strMessageBody, emailAdd, , permFileLocation, , "CodeMsg")
End Sub
A more convenient way of doing work with the thread pool is to use Task.Factory.StartNew(Action). It returns a Task object which can be Awaited or blocked on with Wait.
Once the task completes, the Exception property of the Task can be used to determine whether an exception was thrown and unhandled by the task's subroutine. (If it's not Nothing, then the InnerException property has the real exception that was thrown.)
Dim task = Task.Factory.StartNew(AddressOf WorkFunction)
' do stuff that doesn't depend on WorkFunction having completed
task.Wait()
If task.Exception IsNot Nothing Then Throw task.Exception.InnerException
After a Throw, the sub is exited anyway (the call stack is unwound looking for a Catch), so the Exit Sub statement does nothing. Wrapping a QueueUserWorkItem call in a try block also does nothing, because any exception would occur on the other thread. You would only get exceptions thrown immediately by QueueUserWorkItem, which off the top of my head only includes complaints about the delegate being Nothing.
Asynchronous tasks can also return values. For more information on that, see the TaskFactory methods that return a Func(Of Task).
The project I'm working on is almost ready to ship. Occasionally, I'll encounter an error that won't allow the program to continue running like an out of bounds or a memory limitation.
These kinds of errors
I've been fixing them as I find them, but I'm sure there are others. However, I'm leaving this position in a few days so I need the users to not encounter these.
Is there a way in Vb.net that anytime one of those errors wants to pop up, it can catch it with an message box to the user that says something like "Something really bad happened. Please restart program"?
If it's a winform, you can catch the errors by handling the Application.ThreadException event.
AddHandler Application.ThreadException, AddressOf UIThreadException
Private Shared Sub UIThreadException(ByVal sender As Object, ByVal t As ThreadExceptionEventArgs)
' Handle event here and show message
' Exception is in t.Exception
End Sub
Make sure there's no error in this error handler. I don't think it'll catch exception in other threads.
You can use the Try statement, which is a simple way to handle error.
Here is a simple example:
Try
'Do something
Catch ex As Exception
MsgBox("Error occured")
End Try
Background: I have multithreaded application that has one main UI thread and two threads that are super loops that run for the duration of the program. The worker threads basically read in some information and write an output to a Program Logic Controller.
I am running into an issue that I can't repeat when I'm debugging but only happens when the program is compiled and ran as an executable. I know the proper way of dealing with my issue is to find out why this is happening and deal with it. But while I am doing that I was wondering if it was possible to handle this issue in a different way...
Quesiton :
My entire worker thread is in a
Try
Catch ex As Exception
Finally
End Try
Is it good practice / and even possible for me to dispose of my worker thread in the catch when it hits an exception and then restart / reinstantiate itself in the finally block?
I would Imagine a response to this might be "No thats not good practice because if you hit the exception mid loop, you will lose all the states of all your objects in your thread and if you restart it it might throw things out of sync."
This isn't actually going to be a problem for me, because all the states of all my objects are updated real time on the PLC, and the very first thing I do when I start my worker thread is read from the PLC to get all the states of all my objects.
The root of my question is, can a thread restart itself in the finally block?
If you changed your thread code from this
Do While True
'your code here
Loop
to this
Do While True
Try
'your code here
Catch ex As Exception
End Try
Loop
then the thread can only exit if you have an Exit Do or an exception is thrown by the code in the catch block.
It definitely isn't good practice, but it can be done. However, you would want to restart it in the Catch block, not the Finally block. The Finally block gets called at the end of the Catch, but it also gets called if the Try block finishes execution.
To specifically answer your question; Is it possible? Yes - you can do something like this:
Public Sub Main
'define thread object outside the Try block so we can use it
'again in the Catch block
Dim thr as Thread
Try
thr = New Thread(AddressOf SuperLoop1)
thr.Start
Catch
'you may want to log the exception so you know it has happened
thr = New Thread(AddressOf SuperLoop1)
thr.Start
End Try
End Sub
Sub SuperLoop1
'code for "super loop 1"
End Sub