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Is there any way to execute a method of a com object inside a completely new thread, not attached to the main thread? I have tried using a backgrounWorker, and even using a new thread by doing Dim thr as new Thread(AddressOf blah) and neither work. I am not referencing the COM object anywhere but inside the threaded function "blah" or the backgroundWorker's DoWork method, yet still my main UI locks up as it tries to process the COM object's methods I am calling.
I really need to make this execute the methods from the com object in a separate thread because it is causing my whole application to lock up.
Below is an example of my Thread that uses a method "DoWork". The same logic can be taken for a background worker
Public Sub Reconnect_Scanner() Implements Scanners.Reconnect_Scanner
'Do our request on a new thread
Dim thread As New System.Threading.Thread(AddressOf Connect)
thread.SetApartmentState(Threading.ApartmentState.STA)
thread.Start()
End Sub
Public Sub Connect()
'Get a new instance of our scanner
Dim scanner As New OposScanner_CCO.OPOSScanner
'Loop until scanner is opened
Do
Debug.Print("looking for scanner")
'If we find the device, exit do
Dim openId As Integer = scanner.Open("Honeywell")
If openId = 0 Then Exit Do
'Sleep 1 second
System.Threading.Thread.Sleep(250)
Loop
End Sub
Even though that should be running on a completely new thread, once it does scanner.open my main thread locks up till it is complete.
I appreciate any help.
822
The object can be re-entered if one of its interface method implementations retrieves and dispatches messages or makes an ORPC call to another thread, thereby causing another call to be delivered to the object (by the same apartment). COM does not prevent re-entrancy on the same thread but it provides thread safety.
In C#, the System. Threading. Thread class is used for working with threads. It allows creating and accessing individual threads in a multithreaded application. The first thread to be executed in a process is called the main thread.
Threading support is inbuilt under Common Language Runtime provided by Microsoft . NET Framework. Threads are basically lightweight processes responsible for multitasking within a single application. Threads are managed under the Common Language Runtime, programmers don't have to manage any threads explicitly.
The Thread constructor takes a ThreadStart delegate as a parameter and creates a new thread. The parameter of the ThreadStart is the method that is executed by the new thread. Once a thread it created, it needs to call the Start method to actually start the thread.
COM takes care of the object's threading requirements as published in the registry by the ThreadingModel registry key. Yours is obviously "Apartment", which makes COM take care of thread-safety on the object's behalf. That's very common. And yes, if you created it on the UI thread then COM marshals the call from your worker thread back to the UI thread.
To bypass that, you'd have to create a separate STA thread to give the object another thread-safe home. That requires creating a Thread, calling its SetApartmentState() method to make it STA and calling Application.Run() to run a message loop. That in itself is hard to deal with because you lose control, you'll want a Form or a Timer or Control.BeginInvoke() to generate events that let you use the object's methods. This is all pretty unpleasant, an hourglass cursor was popular in the olden days.
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