Ok, I know this is bad program design, and I'll probably get around to fixing it later, but I'm looking for a quick fix...
I have a C# program that starts a thread that does some work, then in the main thread it starts listening for user input to manually kill the worker. The pseudo-code looks like this:
WorkerClass worker = new WorkerClass();
worker.Start(); //function that starts a new worker thread.
while(!Console.ReadLine().ToUpper().Equals("STOP")){}
worker.Join(); //function that cleanly stops the worker thread.
This works just fine, and originally the worker would always just hang out and continually do stuff, so it made sense to just wait for me to type "stop". However, I've since modified the worker thread so that it eventually reaches the end of it's tasks, and it knows it. Since there's nothing else happening, I'd like the main thread to stop too, but it's still waiting for input from the console. So, is there anyway I can enter text from the worker thread that's read as console input in the main thread?
I do want to keep the ability to manually stop the worker cleanly, so just changing the while statement to check for the worker completion instead of console input isn't really an option.
Rather than doing that, why not have your worker register an event, once the event is raised, you can then kill your loop and exit the application.
Related
My program uses a producer/consumer pattern, meaning that my producer adds tasks to a queue and my consumer executes those tasks in the background whenever there's something in the queue to execute.
My worker thread needs to use a serial port, and the standard way of using a serial port is to open it at the start of the program and keep it open for as long as it's needed (until shutdown). My program is an always-on web service, where usually objects have a lifetime scoped to the request. These two things contradict each other somewhat, so I need to make sure that when I get a request, the background thread is up and running and holding the serial port open instead of opening it for every request which might be more natural in most cases. So my program needs a high degree of self-sufficiency, it needs to detect errors in the worker thread and restart it if needed.
Is there a technique for guaranteeing that my worker thread stays up? I have considered wrapping the entire worker thread's code in a try/catch, and sending an event to the main thread in the finally block so that the worker can be restarted. Or I could continually send "ping" events to the main thread to let it know that the worker thread is still running, or even poll the worker thread from the main thread.
Is there a standard way of doing this? What's the most robust approach? Note that it's fine if the worker thread dies or becomes unable to complete its work for whatever reason - I will just restart the thread and keep trying, however ideally if that happens it should be able to put its task back in the queue.
Examples in C#/F#/dotnet (framework) are greatly appreciated.
I have been googling around for about an hour, and I still don't found any solution.
I simply try to set the maximum value of a progressbar from another thread. So I found the Control.Invoke method. I've been going ahead and implement it:
Now, when I debug my App it simply stucks at the this.Invoke line. The UI comes up, and it is frozen. So I was going ahead and google that out, and it told me to use this.BeginInvoke(). I implemented it, and I was fine, the UI don't freeze.
Thats quiet nice, but in fact the maximum value of my progress bar didn't change :(
What am I doing wrong?
EDIT: Maybe that helps: I am using Parallel.Invoke(); to manage my thread ...
Control.Invoke will only block when it is called on a worker thread and the UI thread is blocked.
The code you posted is correct. You must be blocking the UI thread somewhere else.
I use something similar below in my application which I use to update the actual value for the progress bar. I have changed it a bit from your example. Give it a whirl and see if it helps :)
public void SetMax(int value)
{
if (this.ProgressBar_status.InvokeRequired)
{
this.BeginInvoke(new Action<int>(SetMax), value);
return;
}
this.ProgressBar_status.Maximum = value;
}
I would suggest it is better to use Background worker component which supports reporting progress in the progress bar including other features rather than to call invoke and BeginInvoke. You can find more details about background worker at below MSDN link:
http://msdn.microsoft.com/en-us/library/c8dcext2.aspx
I had the same problem and thanks to Nicholas' answer I realised I had fallen into the same trap in a GUI app to debug a class used in a windows service. The service class runs most of it's code in a thread. The thread was calling back to a logging procedure when it stopped. I was stopping it using a button, and the logging used invoke to update a textbox. The problem was so simple I kicked myself - the invoke was waiting for the button-click to finish, which was waiting for the class to stop which was waiting for invoke to log that it was stopping (repeat until task-manager end process). Solved by creating a thread in the stop button click, with a threadproc to stop the service class. This meant I had to put more code to update form after the stop in another invoke from the new thread, but that worked ok as it wasn't waiting for the main form thread.
In my case, mistake was using join() after starting thread.
join() prevents main thread from execution of codes before child thread completion.
I removed join() command and moved codes after join() to thread and everything worked fine.
I am currently working with threading and backgroundworker in c#. The problem im having is that this. Say i have a main thread for user interaction and a worker thread to process txt files(various editing operations). Then after the backgroundthread runs its contents once, i have a timer start that performs another set of operations. I want these new operations that the timer runs ever x minutes to be run in the same background thread without running the previous txt related operations it ran before the timer started. How can this be done?
You should just use a System.Timers.Timer, which will run its callback on a thread pool thread.
It shouldn't matter which specific thread you run on (as long as it's not the UI thread).
If, for some reason, it does matter (eg, if you're using a single-threaded COM object), you'll need to make a dedicated thread that waits for things to do using a thread-safe queue of delegates.
You want to use an Event Driven method to execute function calls on your worker thread from your UI thread. The way to accomplish this is using BeginInvoke, you can read more about how to use it here: http://www.dreamincode.net/forums/topic/35616-cross-thread-communication-in-c%23/
Add a while loop to the end of your background worker:
while(!stop) { Thread.Sleep(yourIntervalinMilliseconds); ... }
I'd create a stop bool somewhere that the thread looks at when you want it to kick out.
I spawn a thread (only one) to do some work and it pretty much takes care of itself not accessing any data outside of the tread except calling callback() to see if the user wants to quit (also sends a status report back to the main thread to display in the GUI).
When the close closes the exe i would like to wake up the thread and have it quit, whats the best way of doing this? The callback already says if the user wants to quit so now the issue is using Thread.Sleep and waking it up prematurely so it can quit instead of having the process live for another few seconds or minutes. This feature would be nice for stop to exit more quickly.
Another approach would be as follows:
Have a ManualResetEvent in your program and call Set when you want the thread to finish up and close down. Instead of calling Thread.Sleep on your work thread, call event.WaitOne and pass in a TimeSpan object. If the event is signalled, your worker thread will wake up before the timeout occurs - WaitOne will return true.
Use a BackgroundWorker or set your thread's IsBackground property to true, then it won't keep your application open.
I'd recommend the BackgroundWorker, but the latter is a quick fix.
Update
Original poster changed his requirements after posting the question (see comments attached to this question). Update to answer follows:
If you want to stop a background operation without ending the application, please see Background worker's CancelAsync method. Also, don't use Thread.Sleep - use a WaitHandle and call WaitOne on what you need to wait for.
I have to agree with Mark. The only thing clear about your question is that you need to reexamine your threading strategy.
You say you have a thread doing work but then you say you want to wake it up?
Is the thread waiting for work? If so, sleep in shorter cycles and check for exit more often or use a reset event. The best way to wake a thread up is to not put it to sleep. Do what you have to do and exit. Always check for interrupt signals, in whatever form you implement them, before starting any long running operations, and again, if you must sleep the thread, do it in short cycles.
Is the thread busy and you want to interrupt it? You may have no choice but to kill it if you cannot instrument it such that it can respond to interrupt signals in a timely fashion.
I have an application running with the thread,if i perform end-task from the task manager
application is quitting but,in process list an instance will be running(i.e if I do end-task 5 times 5 instances of process running). It might be due to thread.
in this case,if I have to kill all process i need to restart the device :-(.
Manually if I exit It works great.How to overcome from this issue?
I am developing application in c#
As elder_george points out, you have a rogue thread that is preventing the app from exiting and you need to ensure that thread exits when your app shuts down. With CF 3.5 you can usually just set the IsBackground property to truw, though that's not always enough. If the thread is blocking in a system call (like an infinite wait like WaitOne) then the thread will not get schedules and still may not terminate.
The best way to prevent this, and a good practice, is to actually write code that signals your worker threads to shut themselves down. This is often done with a reset event or a boolean flag that the thread checks periodically.
void MyThreadProc()
{
// set this event when the app is shutting down
while(!shutdownEvet.WaitOne(0, false))
{
// do my thread stuff
}
}
This mechanism will also work in CF 2.0 (where IsBackground doesn't exist).
Set IsBackground property on your thread to true.
Hey i got solution for this,
when i perform end task from task manager,control will come next to "Application.Run()" method.
There we can call one user defined function, in that we can perform all the necessary task like killing thread, memory clean up etc.. to end the application smoothly.
Thanks to all for your responses.