I'm extremely novice at threading and I'm simply creating a single thread to run a large function. I've created a messagebox to appear at the end of the function towards the end of the program to tell me the load time it took. As i load the application, the messagebox will appear with a time it took and THEN the thread will kick off(although the UI is navigable while the components are loading from the thread) isn't the point of threading to be able to process multiple functions at the same time? Why is this waiting until the main thread is finished before the new thread kicks off?
I declare and start the new thread early in the app
For every Form in the application's namespace, there will be a default instance created in the My namespace under the Forms property.
----------------------/ Starting Main Thread /-----------------------------------
Private Sub FindCustomerLocation()
Dim Findcontractor_Thread As New Thread(AddressOf **FindContractor_ThreadExecute**)
Findcontractor_Thread.Priority = ThreadPriority.AboveNormal
Findcontractor_Thread.Start(**me**)
End Sub
------------------/ Running Thread /---------------
Private Sub **FindContractor_ThreadExecute**(beginform as *NameOfFormComingFrom*)
Dim threadControls(1) As Object
threadControls(0) = Me.XamDataGrid1
threadControls(1) = Me.WebBrowserMap
**FindContractor_WorkingThread**(threadControls,beginform) ' ANY UI Calls back to the Main UI Thread MUST be delegated and Invoked
End Sub
------------------/ How to Set UI Calls from a Thread / ---------------------
Delegate Sub **FindContractor_WorkingThread**(s As Integer,beginform as *NameOfFormComingFrom*)
Sub **FindContractor_WorkingThreadInvoke**(ByVal s As Integer,beginform as *NameOfFormComingFrom*)
If beginform.mouse.InvokeRequired Then
Dim d As New FindContractor_WorkingThread(AddressOf FindContractor_WorkingThreadInvoke)
beginform.Invoke(d, New Object() {s,beginform})
Else
beginform.Mouse.OverrideCursor = Cursors.Wait
'Do something...
beginform.Mouse.OverrideCursor = Nothing
End If
End Sub
Sources from Pakks answer and Tested!
You have to create multiple threads if you want them to run the way you are thinking (simultaneously).Take a look at this link and try creating more than one thread. This should help your problems. Cheers
http://msdn.microsoft.com/en-us/library/ck8bc5c6%28v=vs.80%29.aspx
Related
Can someone show/tell me where I'm steering wrong with this? I am running a second thread in my application where all it does is read values from registers in a motion controller and then constantly updates those values to the appropriate fields on my UI every 100ms. When I disconnect the controller (ie...Ethernet cable disconnected, so lost comms), I want to destroy/terminate the thread (thread1) completely. When I reconnect the Ethernet cable, I click a button on my UI to reestablish comms to the controller, and execute Runthread() Sub. That is when I want to recreate the thread and start it. However, when debugging this part of the code, it appears that the thread (thread1) is never destroyed even though I have verified that the code does get to that line (Case 1) and execute it. After comms is re-established, the code goes right to Case 3 and starts thread1, where I would expect it to jump to Case 2 and recreate the thread.
Public Class frmMain
Private RMC As RMCLink
Public thread1 As System.Threading.Thread = New System.Threading.Thread(AddressOf ReadRegisters)
Private Sub RunThread()
Dim conditions As Integer
If RMC.IsConnected(PingType.Ping) = False And thread1 IsNot Nothing Then
conditions = 1
ElseIf RMC.IsConnected(PingType.Ping) = True And thread1 Is Nothing Then
conditions = 2
ElseIf RMC.IsConnected(PingType.Ping) = True And thread1 IsNot Nothing Then
conditions = 3
End If
Select Case conditions
Case 1
Thread.Sleep(100)
thread1.Abort()
Case 2
Dim thread1 As System.Threading.Thread = New System.Threading.Thread(AddressOf ReadRegisters)
thread1.Start()
Case 3
thread1.Start()
End Select
End Sub
The documentation (https://msdn.microsoft.com/en-us/library/system.threading.thread.abort(v=vs.110).aspx) states that it usually terminates the thread, but as you've found this doesn't always happen.
One way to accomplish this (I'm sure there are others), is to create a public PleaseDie property that your thread's subroutine(s) check periodically, and if that property is set to True, then exit the subroutines within the thread. Before the thread is started, you'll of course have to reset PleaseDie to False.
So my use for a module is so I can use the same functions across different programs that I develope for my employer. They also want my module to be distributed amongst other programmers so they can use it as well. The programs need to know when there is a thread still running (SQL code is running (there are no problems with the sql side) and it needs to notify the user when all work is done but the user needs to be able to queue work)
From the main form I am using this code:
Dim thread1 As New System.Threading.Thread(AddressOf ModuleTesting.Testing)
thread1.SetApartmentState(Threading.ApartmentState.STA)
thread1.IsBackground = True
thread1.Name = "ModuleLabelCrossThreading"
thread1.Start()
This is the code for my module:
Public Sub Testing()
Form1.threadsrunning += 1
Form1.accesscontrolsmoduletesting()
'THIS IS WHERE THE PROGRAM DOES STUFF ILLUSTRATED BY SLEEPING'
System.Threading.Thread.Sleep(2000)
Form1.threadsrunning -= 1
Form1.accesscontrolsmoduletesting()
end sub
The code to access the controls on the main form is
Public Sub accesscontrolsmoduletesting()
If Me.InvokeRequired = True Then
Me.Invoke(New MethodInvoker(AddressOf accesscontrolsmoduletesting))
Else
If threadsrunning > 0 Then
Label4.Text = threadsrunning & " threads running"
Else
Label4.Text = "0 threads running"
End If
End If
End Sub
I already know the issue is the new thread is creating a new form. I tested this by showing the form and making it wait so it didnt immediately dispose itself and I seen the label was updated. How do I make this thread update the main form instead of just creating a new mainform and then disposing itself after the thread dies?
To reiterate on my Comment you need to get the actual Form1 that is being shown, you should change your Testing Method to accept a Parameter of Form1, then you can use a Parameterized Thread.Start to pass in the Calling Form. You are running into a feature that was left in place to placate Vb6 programmers transitioning to VB.net as this answer by Hans states. And you may find this Blog Post by John Mcllhinney an interesting read.
From Second Link(emphasize mine):
In order to access a form from a secondary thread you generally need to test its InvokeRequired property and then call its Invoke method. I said earlier that there is only ever one default instance of a form class. That’s not strictly true. In fact, default instances are thread-specific, so there is only ever one default instance per thread. As such, if you test the InvokeRequired property of the default instance you will always be accessing the default instance for the current thread, not the one that was displayed on the main thread.
So in response to above I would change your Module Test Method to:
Public Sub Testing(myForm As Form1)
myForm.threadsrunning += 1
myForm.accesscontrolsmoduletesting()
'THIS IS WHERE THE PROGRAM DOES STUFF ILLUSTRATED BY SLEEPING'
System.Threading.Thread.Sleep(2000)
myForm.threadsrunning -= 1
myForm.accesscontrolsmoduletesting()
End Sub
And I would change your Form1's Thread Start Code to look like this.
Dim thread1 As New System.Threading.Thread(AddressOf ModuleTesting.Testing)
thread1.SetApartmentState(Threading.ApartmentState.STA)
thread1.IsBackground = True
thread1.Name = "ModuleLabelCrossThreading"
thread1.Start(Me) 'Note the passing in the instance of the calling Form
After making these few changes your code will work
Dose anybody know how I can make my VB.net application wait until a process is detected as running?
I can find example of how to detect once an exe has finished running but none that detect when an exe is started?
You can use the System.Management.ManagementEventWatcher to wait for certain WMI events to occur. You need to give it a query type and condition to have it watch for the next creation of your process, then get it to do something when that occurs.
For example, if you want :
Dim watcher As ManagementEventWatcher
Public Sub Main()
Dim monitoredProcess = "Notepad.exe"
Dim query As WqlEventQuery = New WqlEventQuery("__InstanceCreationEvent", new TimeSpan(0, 0, 1), "TargetInstance isa ""Win32_Process"" And TargetInstance.Name = """ & monitoredProcess & """")
watcher = New ManagementEventWatcher()
watcher.Query = query
'This starts watching asynchronously, triggering EventArrived events every time a new event comes in.
'You can do synchronous watching via the WaitForNextEvent() method
watcher.Start()
End Sub
Private Sub Watcher_EventArrived(sender As Object, e As EventArrivedEventArgs) Handles watcher.EventArrived
'Do stuff with the startup event
End Sub
Eventually you'll need to stop the watcher, which is you can do by closing the app, or calling watcher.Stop(). This has been written as brain compiler, so if there's any issues let me know.
You could simply wait and check every once in a while whether the process exists. Use Thread.Sleep to avoid busy waiting.
However, this has the possibility that you miss the process if it starts and exists during your wait time.
You can use the below condition
return Process.GetProcesses().Any(Function(p) p.Name.Contains(myProcessName))
Dim p() As Process
Private Sub CheckIfRunning()
p = Process.GetProcessesByName("processName")
If p.Count > 0 Then
' Process is running
Else
' Process is not running
End If
End Sub
OR SIMPLY
System.Diagnostics.Process.GetProcessesByName("processName")
I am trying to create a variable which is of type MyReferenceTypeObject and of value null on thread one, use a delegate to make this thread equal to a new instance of MyReferenceTypeObject on thread two, and then access members of MyReferenceTypeObject back on thread one (in the delegates callback method).
My code is below:
Module Module1
Delegate Sub EditReferenceTypePropertyDelegate(ByVal referenceTypeObject As MyReferenceTypeObject, ByVal numberToChangeTo As Integer)
Sub Main()
Dim editReferenceDelegate = New EditReferenceTypePropertyDelegate(AddressOf EditReferenceTypeProperty)
Dim newReferenceTypeObject As MyReferenceTypeObject
editReferenceDelegate.BeginInvoke(newReferenceTypeObject, 2, AddressOf EditReferenceCallback, newReferenceTypeObject)
Console.ReadLine()
End Sub
Sub EditReferenceTypeProperty(ByVal referenceTypeObject As MyReferenceTypeObject, ByVal numberToChangeTo As Integer)
referenceTypeObject = New MyReferenceTypeObject()
referenceTypeObject.i = numberToChangeTo
End Sub
Sub EditReferenceCallback(ByVal e As IAsyncResult)
Dim referenceObject = DirectCast(e.AsyncState, MyReferenceTypeObject)
Console.WriteLine(referenceObject)
End Sub
End Module
Class MyReferenceTypeObject
Public Property i As Integer
End Class
However, newReferenceTypeObject comes into my callback method as null. I think I understand why, but the problem is that I need to pull some data from a database which I then need to pass into the constructor of newReferenceTypeObject, this takes a couple of seconds, and I don't want to lock up my UI while this is happening. I want to create a field of type MyReferenceTypeObject on thread one, instantiate this on thread two (after I have pulled the data of the database to pass into the constructor) and then work with members of the object back on thread one once the instantiation is complete.
Is this possible? I am using VB.Net with .Net 4.0 on Visual Studio 2012.
If you want to keep the GUI responsive during a long running action, I'd consider using the Task<> library (Comes with .NET 4.0). Here's a quick example.
Sub Main()
Dim instantiateTask = New Task(Of MyReferenceTypeObject)(Function()
' Call your database to pull the instantiation data.
Return New MyReferenceTypeObject With {.i = 2}
End Function)
instantiateTask.Start() ' Start the task -> invokes a ThreadPool.Thread to do the work.
instantiateTask.ContinueWith(Sub(x)
Console.WriteLine(x.Result.I)
End Sub, TaskScheduler.FromCurrentSynchronizationContext())
End Sub
.Wait blocks the GUI thread. However, you could use ContinueWith which is async and therefor nonblocking. Also you need to provide the TaskScheduler ( TaskScheduler.FromCurrentSynchronizationContext ) from the GUI thread to prevent cross-thread exceptions in case you want to update the UI from within the async method.
I have a windows form that gets data from a scale via the serial port. Since I need the operator to be able to cancel the process I do the get data process on a second thread.
The data collection process gets multiple readings from the scale one at a time. The form has a label that needs to be updated with information specific to each reading.
I call the method to get the data from the scale with this code.
Dim ad As New readALine(AddressOf thisScale.readALine)
Dim ac As New AsyncCallback(AddressOf Me.GetDataCallback)
Dim iar As IAsyncResult = ad.BeginInvoke("", ac, ad)
The delegate for the readALine method is defined in the UI code.
Delegate Function readALine(ByVal toSend As String) As String
The GetDataCallback method:
Private Sub GetDataCallback(ByVal ia As IAsyncResult)
.
.
.
lblInstructions.Text = _thisMeasure.dt.Rows(_currRow - 1).Item("cnt") & ":"
lblInstructions.Refresh()
.
.
.
End Sub
I get the exception on the "lblInstructions.Text =" statement.
I thought the GetDataCallback method was part of the UI thread so don't understand why I'm getting the exception. I know this could probably be rewritten using a BackgroundWorker and it's appropriate events but for now would like to understand why this isn't working as expected.
The application was written originally in VS2003 and just recently upgraded to VS2008.
Any insight will be appreciated.
Thanks,
Dave
The problem is a confusion over BeginInvoke. Calling Control.BeginInvoke marshals a delegate call to the UI thread. Calling BeginInvoke on a delegate causes it to be executed on a thread pool thread - and any callback you provide is executed on the same (thread pool) thread. The latter is what you're doing, which is why GetDataCallback is being executed on a thread pool thread, not the UI thread..
So, within GetDataCallback you need to call Control.Invoke or Control.BeginInvoke to marshal back to the UI thread.
One point to note: I very rarely use Control.InvokeRequired these days - it's simpler to unconditionally call Invoke/BeginInvoke; the performance difference isn't usually enough to make up for the benefit in readability, in my experience.
user-interface controls can only be updated by the thread that created them
try
yourForm.BeginInvoke
instead; that should marshall the call to the correct thread
In .NET 1.1 it was possible to perform these cross-thread operations, even though they weren't safe.
In .NET 2.0 the exception you mention is thrown, when you try to perform cross-thread operations such as this, which means that you are performing the UI operations on a non-UI thread, even though you thought you weren't.
Try using the Me.InvokeRequired method to determine whether you are currently on the UI thread. E.g. you could define a method to perform the necessary tasks:
Protected Sub PerformUIOperations()
If Me.InvokeRequired Then
'We are currently on a non-UI thread. Invoke this method on the UI thread:
Me.Invoke(New MethodInvoker(AddressOf Me.PerformUIOperations))
Return
End If
'Perform UI operations when we know it is safe:
lblInstructions.Text = "blabla"
End Sub
The PerformUIOperations method can then be called from any non-UI thread, since it takes care of performing the tasks on the correct thread itself.
Of course, if you need to pass parameters to the PerformUIOperations method (such as information regarding the ongoing operation) you'll have to define a delegate to match the PerformUIOperations method signature and use this instead of the MethodInvoker.
Jon,
I have the following in another section of the code:
Delegate Sub setValueCallback(ByVal row As Integer, ByVal value As Decimal)
Public Sub setValue(ByVal row As Integer, ByVal value As Decimal)
If Me.Controls.Item(_tbIndex(row - 1)).InvokeRequired Then
Dim d As New setValueCallback(AddressOf setValue)
Me.Invoke(d, New Object() {row, value})
Else
Dim tb As TextBox = Me.Controls.Item(_tbIndex(row - 1))
tb.Text = value
_dt.Rows(tb.Tag).Item(1) = value
End If
End Sub
How would this be rewritten to not use .InvokeRequired?
Dave, maybe this is the solution you are looking for:
Dim ad As New readALine(AddressOf thisScale.readALine)
Dim ac As New AsyncCallback(AddressOf Me.GetDataCallback)
Dim iar As IAsyncResult = ad.BeginInvoke("", ac, ad)
Delegate Function readALine(ByVal toSend As String) As String
Private Sub GetDataCallback(ByVal ia As IAsyncResult)
If lblInstructions.InvokeRequired Then
lblInstructions.Invoke(New AsyncCallback(AddressOf GetDataCallback), New Object() {ia})
Else
.
.
lblInstructions.Text = _thisMeasure.dt.Rows(_currRow - 1).Item("cnt") & ":"
lblInstructions.Refresh()
.
.
End If
End Sub