I have a process that I would like to be able to cleanly shut down from an external process. That is, I would like to give it a chance to clean up it's resources (save it's data etc.) before it dies.
Process.CloseMainWindow appears to be the ordinary way to go, except the process in question doesn't have any windows and I don't want to immediately call Process.Kill because I want to give it chance to clean up first (and a kill process command can't be intercepted by the target process).
So what is the best way to allow my process to be shut cleanly from another process?
I have control over both processes. The process to be shut does have a message loop (Application.Run()) so I would think there would be some message I could post through there.
I have read the msdn article on terminating processes and this article about closing processes cleanly however both mention methods that seem quite sophisticated despite the simplicity of what I am trying to achieve. Given that I have control over both processes I am hoping there's something a bit simpler that can be implemented cleanly in C#. Is there one?
The process to close is not a service, so can't do service stop.
I'm not sure if a .NET message loop supports thread messages, or only window messages. If it supports thread messages, then the terminating app can use PostThreadMessage() to post a WM_QUIT message (or a custom message that the message loop can look for) to the main thread of the target process so it can stop its message loop and exit the app.
Otherwise, have the target app create a named kernel event object using EventWaitHandle and then wait on the event, either by calling EventWaitHandle.WaitOne() in a manual thread, or calling ThreadPool.RegisterWaitForSingleObject() to use a system-provided thread pool. When the event is signaled, you can notify the main thread to exit the app. The terminating app can then open the event object by name using EventWaitHandle.OpenExisting(), and then signal the event with EventWaitHandle.Set().
Related
I'm creating an application that's going to be continuously listening out for incoming signals via TCP until it's either stopped via a button, or the application closes. Being as the PC that the application is running on needs to run quite CPU-heavy stuff, I figured I should run this in a separate thread so that it doesn't hog the CPU.
My thoughts are to use a BackgroundWorker containing an inner-loop in DoWork() that checks the IsCancellationPending flag (this is set via the CancelAsync() method when the user clicks the stop button or exits the application). Is this the best route to go, or is there some other method that's more accepted?
You're doing an IO bound operation, so you shouldn't even be using another thread at all. You should be handling the work asynchronously, in which an event, callback, Task, etc. fires to indicate that you have a message to process, which you can process and then go back to not using any thread at all.
Creating a thread that's just going to spend the vast majority of its time sitting there doing nothing while you wait for network activity isn't a productive use of resources.
Windows Mobile 6.5
I have a process which uses System.Threading.Timer upload some data to net at specified intervals.
Now I want to terminate this process from a GUI application. I can use process enumerator to get Process object. What happens when I call Process.Kill? Does it jsut terminate it, the process could be in the middle of reading/deleting data from local database and sending it to service. What can I do make sure that atleast if its in middle it does not terminate and once it is done it can terminate before next Timer event fires?
Terminating an application like that cuts it off at the knees, introducing the distinct possibility of corrupting data. The only way around that is to not terminate the process.
You'll have to introduce a way to communicate to the application that it need to exit so that it can finish whatever it's doing so data won't be corrupted.
i.e. the application must be written in a way to accept a request like that (however you want to do it).
Here is the situation:
I have to create a program that would input another processes output stream into textbox. That it self wouldn't cause too much problem. What does, however, is the fact that I have to run 5 instances of this console application and redirect output to 5 textboxes, as well as to be able to kill any of these processes at any time. As far as I have learned, the best way to do this is asynchronously. But the problem here is with killing processes, that are created on different thread. How do I kill it without having access to it since it doesn't exist in scope where I have to kill it. My best guess is to get its PID on Process.Start(), so I can kill it, so...
Is it possible to fire any event from process on Process.kill() command?
And if not - is there a way to kill a process in about the same time interval as Process.Kill() that does fire some sort of event?
Or maybe someone could suggest me some other approaches or best practice on how these problems are usually solved?
EDIT: The reason I am running all processes on different threads is that I use Thread.Sleep() on some of them if there is and input parameter that tell me that the process must be killed after x seconds.
Process.Kill() command for some reason, does, in fact, fire process exited event. Easiest way for me to know that the process was killed, was by making a volatile string that holds information about how it ended. (Change it to "killed" before process.kill etc...)
First of all you do not need Threads at all. Starting a process is async in itself, so Process.Start(...) does not block and you can create as many processes as you want.
Instead of using the static Process.Start method you should consider creating Process class instances and set the CanRaiseEvents property to true. Further there are a couple of events you can register (per instance) - those will only raise if CanRaiseEvents is set to true, but also after a process is/has exited (including Kill() calls).
When you call
Process.Start()
it returns a Process class instance, which you can use to retrieve information from it output and kill that process any time
Process p = Process.Start("process.exe");
//some operations with process, may be in another thread
p.Kill()
I am having problems closing an application that uses WaitForSingleObject() with an INFINITE timout.
The full picture is this. I am doing the following to allow my application to handle the device wakeup event:
Register the event with:
CeRunAppAtEvent("\\\\.\\Notifications\\NamedEvents\\WakeupEvent",
NOTIFICATION_EVENT_WAKEUP);
Start a new thread to wait on:
Thread waitForWakeThread = new Thread(new ThreadStart(WaitForWakeup));
waitForWakeThread.Start();
Then do the following in the target method:
private void WaitForWakeup()
{
IntPtr handle = CreateEvent(IntPtr.Zero, 0, 0, "WakeupEvent");
while (true)
{
WaitForSingleObject(handle, INFINITE);
MessageBox.Show("Wakey wakey");
}
}
This all works fine until I try to close the application when, predictably, WaitForSingleObject continues to wait and does not allow the app to close properly. We only allow one instance of our app to run at a time and we check for this on startup. It appears to continue running until the device is soft reset.
Is there a way to kill the handle that WaitForSingleObject is waiting for, to force it to return?
Many thanks.
Use WaitForMultipleObject instead, and pass 2 handles. The existing one, and one for an event called something like 'exit'. During app shutdown, SetEvent on the exit event, and the WaitForMultipleObject will return and you can get it to exit the thread gracefully.
You need to switch on the return value of WaitForMultipleObject to do the appropriate behaviour depending on which one of the handles was triggered.
Possibly, also, you can set the thread to be a background thread. This will prevent it from stopping your application from shutting down when the main thread terminates.
See:
http://msdn.microsoft.com/en-us/library/system.threading.thread.isbackground.aspx
This is what I would do...
Use the EventWaitHandle class instead of calling CreateEvent directly. There shouldn't be any need to use the Windows API other than CeRunAppAtEvent (and API calls make code ugly...). Get this working first.
Before creating the thread, create a ManualResetEvent variable that is not initially flagged. Call it "TerminateEvent".
Replace the WaitForSingleObject API call with WaitHandle.WaitAny(WaitHandle[]) and pass an array containing "TerminateEvent" and the EventWaitHandle class wrapping the CeRunAppAtEvent notification.
Your loop can use the return value of WaitAny to determine what to do. The return value is the array index of the wait handle that unblocked the thread, so you can determine whether to continue the loop or not.
To cleanly end the thread, you can call "Set" on your "TerminateEvent" and then "Join" the thread to wait for it to terminate.
'This all works fine until I try to close the application when, predictably, WaitForSingleObject continues to wait and does not allow the app to close properly.'
Any app can close, no matter what its threads are doing. If you call ExitProcess(0) from any thread in your app, the app will close, no matter if there are threads waiting INFINITE on some API/sychro, sleeping, running on another processor, whatever. The OS will change the state of all theads that are not running to 'never run again' and use its interprocessor driver to hard-interrupt any other processors that are actually running your thread code. Once all the threads are stopped, the OS frees handles, segments etc and your app no longer exists.
Problems arise when developers try to 'cleanly' shut down threads that are stuck - like yours, when the app is closing. So..
Do you have a TThread.WaitFor, or similar, in an OnClose/OnCloseQuery handler, FormDestroy or destructor? If you have, and have no vital reason to ensure that the thread is terminated, just comment it out!
This allows the main form to close and so your code will finally reach the ExitProcess() it has been trying to get at since you clicked on the red cross button
You could, of coure, just call ExitProcess() yourself, but this may leave you with resources leaked in other proceses - database connections, for example.
'216/217 errors on close if I don't stop the threads'. This often happens because developers have followed the er... 'unfortunate' Delphi thread examples and communicate with threads by directly exchanging data between secondary thread fields and main thread fields, (eg. TThread.synchronize). This just sucks and is hell-bent on causing problems, even in the app run, never mind at shutdown when a form has been destroyed and a thread is trying to write to it or a thread has been destroyed and a main-thread form is trying ot call methods on it. It is much safer to communicate asynchronously with threads by means of queueing/PostMessaging objects that outlive both of them, eg. objects created in the thread/form and freed in the form/thread, or by means of a (thread-safe), pool of objects created in an initialization section. Forms can then close/free safely while associated threads may continue to pointlessly fill up objects for handling until the main form closes, ExitProcess() is reached and the OS annihilates the threads.
'My Form handle is invalid because it has closed but my thread tries to post a message to it'. If the PostMessage excepts, exit your thread. A better way is similar to the approach above - only post messages to a window that outlives all forms. Create one in an initialization section with a trivial WndProc that only handles one const message number that all threads use for posting. You can use wParam to pass the TwinControl instance that the thread is trying to communicate with, (usually a form variable), while lParam passes the object being communicated. When it gets a message from a thread, WndProc calls 'Peform' on the TwinControl passed and the TwinControl will get the comms object in a message-handler. A simple global boolean, 'AppClosing', say, can stop the WndProc calling Peform() on TwinControls that are freeing themselves during shutdown. This approach also avoids problems arising when the OS recreates your form window with a different handle - the Delphi form handle is not used and Windows will not recreate/change the handle of the simple form created in initialization.
I have followed these approaches for decades and do not get any shutdown problems, even with apps with dozens of threads slinging objects around on queues.
Rgds,
Martin
Of course the preferable way to solve this is to use WaitForMultipleObjects, or any other suitable function that is able to wait for multiple criterias (such as WaitForMultipleObjects, MsgWaitForMultipleObjects, etc.).
However if you have no control over which function is used - there're some tricky methods to solve this.
You may hack the functions imported from system DLL, by altering in memory the import table of any module. Since WaitForMultipleObjects is exported from kernel32.dll - it's ok.
using this technics you may redirect the function caller into your hands, and there you will be able to use the WaitForMultipleObjects.
I have a c# .NET multi-threaded application that is freezing the interface. What is unusual about this is that the interface does not freeze unless I let the system sit idle long enough for the screen saver to start (which requires me to reenter my password to re-gain access to the system). When the interface becomes visible again (after I have successfully entered my password) all the windows are white. I can see the window titles, move the windows around, minimize them and such, but the screens are not repainting. When I break all and enter the debugger, the call stack has Application.Run(), external code, and then "in a sleep, wait, or join". I put break points in all four of the threads I open and they are still running, it is just the main app's UI thread that is blocked. When I look at my thread list, what was my main thread and my four worker threads now consists of my main thread and 11 worker threads. I didn't open this many threads so it must be the serialport class.
Now let me describe my program.
My main app allows users to collect and monitor data from serial ports. I have implemented this in the following way. When a connection is desired, a button is pressed on the main app which calls a function in a DLL which opens a status window and then launches a thread which monitors the serial port. When that function returns, the main app launches a thread to monitor a queue created in the DLL when it is initialized. When data is received from the serial port, the data is parsed and then the status window is updated (via a delegate) and the data is pushed onto the queue. When the main apps worker thread sees data in the queue it retrieves it and posts it in a list box on the main app, using a delegate. In all cases I use BeginInvoke to call these delegates.
My DLL contains two libraries for the two different types of equipment it can communicate with.
This problem occurs when I have a connection to two devices; hence the four worker threads two for each device. The DLL itself is setup as a comm object so I can access it easily from a C++/MFC app and a c# app, both of which utilize it.
I found that if I add code to the thread inside the DLL so it calls Application.DoEvents() every 30 seconds, the interface will be frozen for about 30 seconds and then resume activity like normal. I figure something is blocking the main thread and forcing DoEvents() to fire seems to break the lock, but I have no idea what might be causing this lock. This is not a solution, just something of interest.
I would appreciate any suggestions you might have. Thanks.
I found that if I add code to the thread inside the DLL so it calls Application.DoEvents() every 30 seconds, the interface will be frozen for about 30 seconds and then resume activity like normal. I figure something is blocking the main thread and forcing DoEvents() to fire seems to break the lock, but I have no idea what might be causing this lock. This is not a solution, just something of interest.
I would recommend running your program under the new Visual Studio 2010 Concurrency Profiler. This will show you, at runtime, which threads are blocked, and which objects they are waiting on. Thread contention is explicitly marked and highlighted for you.
You can use this to easily determine what code is causing the deadlock on your UI thread.
Try changing your Thread Start code to Thread.Start() instead of BeginInvoke(). BeginInvoke does not keep threads tryky seperate from your UI, as it and it may be interacting strangely with DoEvents. You can read up on BeginInvoke and how it works here: http://www.codeproject.com/KB/cs/begininvoke.aspx
Also, DoEvents is NEVER necessary in an application, and can cause a lot of unexpected behavior. Use threadding with UI calls wrapped in a Control.Invoke(...) statement. If you're using .NET 3.5+, you can make this easy with delegates that look like this: Invoke((Action)delegate() {*code goes here*});