We have an application written in .net, c#, winforms. We noticed that sometimes when closing the application, the process remains.
I'm not sure how I can reproduce that behavior, so I'm looking for some clues as to why the application wouldn't exit.
The application uses a bit of background threads. Thread pools. Wondering if that could be the cause. Anything else could have this effect?
If you have thread's that have IsBackground property set to false that are alive after application is closed, they will remain
The application uses a bit of
background threads. Thread pools.
Wondering if that could be the cause.
Anything else could have this effect?
It most definitely could be the cause though I cannot be certain that it actually is. One way to test this hypothesis to make sure all threads that have been explicitly created are designated as background threads. This can be done by setting Thread.IsBackground = true which will allow the application to terminate if the main thread ends. If there is at least one thread for which IsBackground = false then the CLR keeps the host process running.
Its likely to be a thread left running. If you have a look at the process in task manager you can see when a thread starts, and how many are left running when it exits by adding the 'Threads' column from the view menu.
I would start by making sure you start and end on the same thread count.
Get Process Explorer and possibly Process Monitor and see what thread is left suspended or running.
If you are able to run in debug and you close the form, VS should not return to the normal code edit mode (it will still have the pause and stop buttons from debug active). You can then press Pause and check the Threads window to see where the call stacks are stuck for threads that are still active.
Related
I have a Windows Service that when it gets started It creates many backgroundworkers. and each backgroundworker monitors its own Queue in memory with the pending items to process.
When the process that created the backgroundworkers --windows service-- is stopped (either by request or because it crashed) are these background workers stoped or left orphan and still running ?
Do I need to write the code stop the backgropund workers when the windows service is about to be stopped ?
BackgroundWorkers use threads with IsBackground set to true, which means it will terminate when all non-background threads have terminated.
If your BackgroundWorker is going to do something where it should not be shut-down until it is completed, then it should set Thread.CurrentThread.IsBackground = false before it begins that crucial part, and set it back to true upon completion.
Edit: It's worth adding, that a process shutdown (unhandled exception, process killed through the task-manager or replacement, etc.) will end all threads. It's rather the reverse; ending all non-background threads will end the process (and take all background threads with them). It's this you need to worry about in terms of reacting to user input requesting the process terminate (service stop, last visible window closed, etc.)
In .NET applications and services when the main thread terminates all child background threads terminate as well.
I am trying to figure out what changed within a project that now causes the application to not exit the debugger when I close the application I am debugging. I have also noticed that unhandled exceptions no longer invoke the unhandled exception handler, I am not sure if it's related.
This is probably due to other threads, which are not set as background threads, keeping the application alive. Background threads will terminate when the application does, whereas foreground threads will keep the rest of the application alive until they complete.
One way to check for the thread(s) that are responsible is in the debugger, as follows:
Run your app in the debugger
"Exit" your app.
Wait until the app should have exited but hasn't
Break into the app using the "pause" button
Open the "Threads" debugging window
Look for any threads in this window. Chances are there will be one, or a few threads showing. See if you can identify what they are by the info in the window.
It may also help to open the "Stack" debugging window and then double-click on each thread in the "Threads" window in turn and look at the contents of the "Stack" window. You may be able to see what any stuck threads are trying to do.
The debugger exits when all the threads exit. You've probably created an extra thread and done nothing to terminate it.
And this would explain unhandled exceptions being uncaught: if they happen on a different thread you won't see them on the main thread.
Most certainly the application has not actually terminated. Do you have any other threads running? An application will not shut down until all foreground threads have terminated.
I'm trying to figure out why the application process lingers in Task Manager after the application is closed and the window disappears.
When I get VS to attach to the zombie process and break all, the threads window shows that the main thread is still alive, and a number of worker threads as well.
Some questions:
Are worker threads necessarily background threads? If not, how do I identify the background threads as I didn't see such a column in the window?
Do I simply double-click on each thread in the thread window, and watch the Thread.IsBackgroundThread value?
When I click on the main thread, the debugger doesn't show a call stack. How
do I identify where the main thread is stuck?
I would strongly sugest you tu use WinDbg. It is not a visual debugger though it is much more powerful.
Surely I will figure you out.
To list all threads in a process use: ~.
To switch to a certain thread ~thread_ids.
To see stak of curent thread !clr_stack.
Brief tutorial.
http://www.codeproject.com/KB/debug/windbg_part1.aspx
Also try in google "Debuging Asp.net with windbg"
I a WPF/C# application that has a psuedo-process of
Click a button > Start a thread to take a picture from a web cam API > Instantiate the web cam API > API starts a callback thread > Picture is taken > API object is disposed
These steps generally work except for the last portion where the callback thread to the web cam API does not close out. So, in my Task Manager, I invariably end up with a "ghost" process, which shares the same name as my base WPF application. Also, making a second call to the same web cam API (to take a second picture) fails miserably.
So, I'm trying to find a way to make sure that all of my threads from my root application are forcibly closed out at all times. Is there a way to ensure that no threads are left over?
If you set IsBackground to true on those threads they will be terminated at shutdown.
If you have a window in your app, set the Application.ShutdownMode to OnMainWindowClose. That will terminate any running background threads for you when the main window closes. Programatically you can call Environment.Exit to kill all threads as gracefully as possible (but forcefully if not) and exit the application.
If you see some ghost process besides your main program, it is not a thread problem. You've created other process to perform the operation. Kill it. Your resources will be released. You don't have to worry about threads being running when there is a lot bigger problem - other process hanging on to resources.
After I close the main window of my program, the process is still running in the background.
How can I check what is the cause for this weird problem?
(I don't know which part of my program code is relevant)
First check that the value of your application's ShutdownMode property is equal to ShutdownMode.OnMainWindowClose -- if it is not, see if the actual value is preventing the app from closing.
If this does not solve the problem, then you have one or more non-background threads still running after the main window closes, preventing the process from shutting down. Break into the debugger and see how many threads are still alive and what they are doing; this will lead you to a solution.
To see the Thread that is currently running and stopping your application from termination just press "Break All" at the Visual Studio and see where the cursor stops.
Note: you can force application to terminate by calling Environment.Exit();
Another reason could be that someone set the Application.ShutdownMode to OnExplicitShutdown.
One possibility is that you create threads which are not set to background or you're calling code that does that; that may keep your process "alive" even after you shut down your main thread.
Make sure that you terminate all of your threads before you exit or you set their IsBackground property to true.