I'd like to implement timeout mechanism for scripts, executed through Roslyn, so I need a way to abort a script execution. The only solution I found so far, is executing the script inside a thread and terminating it, but it's obviously a flawed solution.
Is there a better way to do this?
Other than you launching a separate process and killing that instead (to avoid the standard pitfalls of Thread.Abort()), that's the best you can do. Given the script code can be more or less arbitrary, there really couldn't be a better option. All it takes is your script to do Thread.Sleep(Timeout.Infinite) and there's nothing the scripting engine could do to recover that.
First create a new thread and put your code inside the thread as an action. Then call the Thread.Start method to begin execution. Use Thread.Join method to wait until the thread completes its execution.
In the below code, if the thread execution does not complete in 6 seconds then the thread is interrupted.
Here is the code:
Thread thread = new Thread(() => {
try
{
// your code related to Roslyn is here
// ...
}
catch (Exception ex)
{
}
});
thread.Start();
if (!thread.Join(TimeSpan.FromSeconds(6)))
{
thread.Interrupt();
}
The above code ends compilation after 6 seconds.
Related
I am using BackgroundWorker for processing a long running external operation. However the user have option to cancel the background operation. Since my custom BackgroundWorker supports Thread.Abort(), all I am doing is BackgroundWorker.Abort() when user triggers Cancel from main thread.
But the thread is not actually terminating, it is still completing the external process. Is there any way I can terminate a thread instantly.
I do not have control on the external processing, so cannot send any flag for approach like while (checkThreadCancelled){}.
Below is my pseudo code.
Any help?
AbortableBackgroundWorker _bgWorker;
void MainThreadFunc()
{
_bgWorker = new AbortableBackgroundWorker();
_bgWorker.DoWork += new DoWorkEventHandler(bg_DoWork);
_bgWorker.RunWorkerCompleted += new RunWorkerCompletedEventHandler
( bg_RunWorkerCompleted );
_bgWorker.WorkerSupportsCancellation = true;
_bgWorker.RunWorkerAsync();
}
void bg_DoWork()
{
//Call external dll function for processing
}
void bg_RunWorkerCompleted()
{
//Process completed code
}
void CancelBgProcess()
{
if(_bgWorker != null)
_bgWorker.Abort();
}
The Abort method relies on worker thread cooperating with it. Ultimately it causes the CLR to throw an exception indicating that the thread is to abort, which the thread is free to deal with as it pleases.
As your worker thread is executing something in a DLL, the CLR isn't in control and therefore it does not have the option to throw an exception.
You have the option of using the Win32 TerminateThread API, but doing so is severe and may or may not lead to corruption within your process. TerminateThread is not really an option that you should ever choose.
Since you cannot modify the library that you are calling, you are left with two options. The first and easiest approach, lower the priority of the background thread and ignore the fact that it continues to run after cancellation.
The second is to launch your background operation in a separate process rather than thread. At which point, you may terminate the entire process if the operation is cancelled. If you go this route, you will need to pick some form of IPC to communicate the input and output parameters of the library.
Tasks and CancellationTokens ultimately will not help you in this situation as you will end up in the same place: executing library code that will not cooperate with you in order to be cancelled.
You don't want to use Thread.Abort, it is typically considered bad practice. There are many questions asked on SO that provide some very good explanations. For example: Timeout Pattern - How bad is Thread.Abort really?
Try looking at Tasks and CancellationTokens. See this MSDN article: http://msdn.microsoft.com/en-us/library/dd997396.aspx
Try this:
if (_bgWorker.IsBusy)
{
_bgWorker.WorkerSupportsCancellation = true;
//To cancel the Thread if Closing the Application
//while the Background Thread Worker is Still running on Background.
_bgWorker.CancelAsync();
}
It will stop the current thread process and will cancel the ongoing operation on that thread.
May be it helps you
I have the following code:
public class GUI
{
public void threadTask()
{
while(MY_GLOBAL_VARIABLE)
{
// do something
}
}
}
// Execute Thread
GUI gui = new GUI();
Thread t = new Thread(threadTask);
t.Start();
This seems like a messy way to do this. Any better approach how to reference it and kill it instantly? Thanks!
UPDATE: who ever gave me a downvote, LEARN TO READ! I clearly specified what I'm trying to 'kill' in the title, tags and code, at least next time read the post before casting a vote.
What you have is fine, the thread will be cleaned up as soon as it's finished processing.
You don't kill/dispose a thread, it has no IDisposable.
You could put the thread start in a method, so you can call it more then once, when it finished the first time.
You can use:
t.Join();
to catch when the thread finished.
The call to Join() is what de-allocates the thread. You don't have to do anything else. Just make sure that the threads clean up any resources they might be using before they exit.
I have a thread:
void threadCode(object o)
{
doStuffHere(o); // Blocking call. Sometimes hangs.
}
and I'm calling it like this:
Thread t = new Thread(new ThreadStart(delegate()
{
threadCode(o);
}));
t.Start();
StopWatch sw = new StopWatch();
sw.Start();
while (t.IsAlive)
{
Application.DoEvents();
if (sw.EllapsedMilliseconds > myTimeout)
// Somehow kill t even though doStuffHere(o) is blocked (but hung)
}
I'm using the .NET Zip Library and calling ZipFile.CommitUpdate() which works most of the time, but sometimes just hangs. I don't know why, I can't see anything in the documentation which specifies why this is happening. A small file which should take no longer than 5 - 10 seconds will sometimes sit there for more then 5 minutes with no progress. I/O graphs in process explorer show that the process is not reading or writing, and there is no CPU usage. Basically, if this happens, I want to kill CommitUpdate() and try again once or twice before giving up.
Any idea how I can kill a thread stuck in a blocking call?
(Alternatively - those of you with experience with this zip library: do you know why it might be hanging with some files sometimes? I'm modifying the contents of .docx and .pptx (GZip) files. This would be an ideal solution.)
If you're going to terminate the hanging thread by using Thread.Abort(), make sure you handle ThreadAbortException in your thread code. The normal pattern is:
try {
// do work here
}
catch (ThreadAbortException) {
// allows your thread to gracefully terminate
Thread.ResetAbort();
}
catch {
// regular exception handling
}
If you don't follow the above pattern, then at best your threads will terminate ungracefully. At worst, you could run into a number of other problems.
You can call Thread.Abort to bloodily murder the thread.
The thread will not be able to clean up after itself (except for finally blocks); depending on exactly what it was doing at the time, it could seriously mess up your program.
DO NOT use Thread.Abort() to workaround a bug in a library you're using. (Or it could be a bug in your code).
Either get the original bug fixed, or move to a different library.
ps: You might want to try DotNetZip, in lieu of SharpZipLib.
Alternative to using a Stopwatch, you could do this:
Thread thread = new Thread(new ThreadStart(delegate()
{
threadCode(o);
}));
thread.Start();
thread.Join(myTimeout);
if(thread.IsAlive)
{
thread.Abort();
}
Use the Thread.Abort() method to kill a thread. See http://msdn.microsoft.com/en-us/library/aa332365(VS.71).aspx for more details.
As a last resort you could use Thread.Abort() to terminate the thread - don't expect any orderly shutdown.
I haven't done this myself, so I not sure about this, but does t.Abort(); do the trick?
I've got a thread that goes out and looks up data on our (old) SQL server.
As data comes in, I post information to a modal dialog box - the user can't & shouldn't do anything else while all this processing is going on. The modal dialog box is just to let them see that I'm doing something and to prevent them from running another query at the same time.
Sometimes (rarely) when the code makes a call to the SQL server, the server does not respond (IT has it down for maintenance, the LAN line got cut, or the PC isn't on the network) or the person doing the query runs out of time. So, the modal dialog box does have a cancel button.
The Thread object (System.Threading.Thread) has IsBackground=true.
When someone clicks Cancel, I call my KillThread method.
Note: I can NOT use the BackgroundWorker component in this class because it is shared with some Windows Mobile 5 code & WM5 does not have the BackgroundWorker.
void KillThread(Thread th) {
if (th != null) {
ManualResetEvent mre = new ManualResetEvent(false);
Thread thread1 = new Thread(
() =>
{
try {
if (th.IsAlive) {
//th.Stop();
// 'System.Threading.Thread' does not contain a definition for 'Stop'
// and no extension method 'Stop' accepting a first argument of type
// 'System.Threading.Thread' could be found (are you missing a using
// directive or an assembly reference?)
th.Abort();
}
} catch (Exception err) {
Console.WriteLine(err);
} finally {
mre.Set();
}
}
);
string text = "Thread Killer";
thread1.IsBackground = true;
thread1.Name = text;
thread1.Start();
bool worked = mre.WaitOne(1000);
if (!worked) {
Console.WriteLine(text + " Failed");
}
th = null;
}
}
In my Output Window, I always see "Thread Killer Failed" but no exception is ever thrown.
How should I stop a thread?
The best related posts I found where the two below:
How to Kill Thread in C#?
How to kill a thread instantly in C#?
EDIT:
There seems to be some confusion with the method I listed above.
First, when someone clicks the cancel button, this routine is called:
void Cancel_Click(object sender, EventArgs e) {
KillThread(myThread);
}
Next, when I go in to kill a thread, I'd rather not have to wait forever for the thread to stop. At the same time, I don't want to let my code proceed if the thread is still active. So, I use a ManualResetEvent object. It should not take a full second (1000ms) just to stop a thread, but every time the WaitOne method times out.
Still listening for ideas.
Short Answer: You don't. Normally you do it by signaling you want to quit.
If you're firing an SQL query, do it asynchronously (pardon my spelling), and cancel it if necessary. That really goes for any lengthy task in a separate thread.
For further reading see Eric Lippert's articles:
Careful with that axe, part one: Should I specify a timeout? and Careful with that axe, part two: What about exceptions?
Edit:
How do you call SQL Server? ADO, TDS, Standard/Custom Library, etc... ?
THAT call should be made asynchrone.
Thus: StartOpeningConnection, WaitFor OpeningComplete, StartQuery, WaitFor QueryComplete, Start CloseConnection, WaitFor CloseConnectionComplete etc. During any of the waits your thread should sleep. After waking up, Check if your parent thread (the UI thread) has cancelled, or a timeout has occurred and exit the thread and possibly inform sqlserver that you're done (closing connection).
It's not easy, but it rarely is...
Edit 2:In your case, if you are unable to change the database code to asynchrone, make it a seperate process and kill that if neccesary. That way the resources (connection etc.) will be released. With threads, this won't be the case. But it's an ugly hack.
Edit 3:
You should use the BeginExecuteReader/EndExecuteReader Pattern.
this article is a good reference:
It will require rewriting your data access code, but it's the way to do it properly.
I get the feeling that giving the Thread 1000ms to abort is simply not enough. MSDN recommends that you call Thread.Join. It would definitely be helpful to see the code that is being aborted.
Thread.Abort
The thread is not guaranteed to abort
immediately, or at all. This situation
can occur if a thread does an
unbounded amount of computation in the
finally blocks that are called as part
of the abort procedure, thereby
indefinitely delaying the abort. To
wait until a thread has aborted, you
can call the Join method on the thread
after calling the Abort method, but
there is no guarantee the wait will
end.
What are you passing into your KillThread method? The cancel button will be being clicked on the UI thread, not the one that you want to kill.
You should signal your event when the user clicks Cancel (not kill the thread). In your example, the ManualResetEvent "mre"'s scope should be outside the thread function.
To answer the more general question of how to force kill any kind of Thread in C#:
If any unhandled Exception is thrown inside a thread (including those used by Task and other ways of running asynchronously), this thread will be terminated.
However note that this comes with many problems, like resources not being freed, improper memory management, general undefined behavior etc, and the unhandled Exception may still have to be handled by its parent thread (wherever it was started from) OR by registering for the following Event beforehand, depending on how the thread was started:
AppDomain.CurrentDomain.UnhandledException += YourEventHandler;
I should emphasize again that this should be an absolute last resort. If you need this, your applications is almost certainly designed poorly and there are probably different solutions you should use. There are good reasons why Thread.Abort is now deprecated and no longer functional.
how do set a timeout for a busy method +C#.
Ok, here's the real answer.
...
void LongRunningMethod(object monitorSync)
{
//do stuff
lock (monitorSync) {
Monitor.Pulse(monitorSync);
}
}
void ImpatientMethod() {
Action<object> longMethod = LongRunningMethod;
object monitorSync = new object();
bool timedOut;
lock (monitorSync) {
longMethod.BeginInvoke(monitorSync, null, null);
timedOut = !Monitor.Wait(monitorSync, TimeSpan.FromSeconds(30)); // waiting 30 secs
}
if (timedOut) {
// it timed out.
}
}
...
This combines two of the most fun parts of using C#. First off, to call the method asynchronously, use a delegate which has the fancy-pants BeginInvoke magic.
Then, use a monitor to send a message from the LongRunningMethod back to the ImpatientMethod to let it know when it's done, or if it hasn't heard from it in a certain amount of time, just give up on it.
(p.s.- Just kidding about this being the real answer. I know there are 2^9303 ways to skin a cat. Especially in .Net)
You can not do that, unless you change the method.
There are two ways:
The method is built in such a way that it itself measures how long it has been running, and then returns prematurely if it exceeds some threshold.
The method is built in such a way that it monitors a variable/event that says "when this variable is set, please exit", and then you have another thread measure the time spent in the first method, and then set that variable when the time elapsed has exceeded some threshold.
The most obvious, but unfortunately wrong, answer you can get here is "Just run the method in a thread and use Thread.Abort when it has ran for too long".
The only correct way is for the method to cooperate in such a way that it will do a clean exit when it has been running too long.
There's also a third way, where you execute the method on a separate thread, but after waiting for it to finish, and it takes too long to do that, you simply say "I am not going to wait for it to finish, but just discard it". In this case, the method will still run, and eventually finish, but that other thread that was waiting for it will simply give up.
Think of the third way as calling someone and asking them to search their house for that book you lent them, and after you waiting on your end of the phone for 5 minutes you simply say "aw, chuck it", and hang up. Eventually that other person will find the book and get back to the phone, only to notice that you no longer care for the result.
This is an old question but it has a simpler solution now that was not available then: Tasks!
Here is a sample code:
var task = Task.Run(() => LongRunningMethod());//you can pass parameters to the method as well
if (task.Wait(TimeSpan.FromSeconds(30)))
return task.Result; //the method returns elegantly
else
throw new TimeoutException();//the method timed-out
While MojoFilter's answer is nice it can lead to leaks if the "LongMethod" freezes. You should ABORT the operation if you're not interested in the result anymore.
public void LongMethod()
{
//do stuff
}
public void ImpatientMethod()
{
Action longMethod = LongMethod; //use Func if you need a return value
ManualResetEvent mre = new ManualResetEvent(false);
Thread actionThread = new Thread(new ThreadStart(() =>
{
var iar = longMethod.BeginInvoke(null, null);
longMethod.EndInvoke(iar); //always call endinvoke
mre.Set();
}));
actionThread.Start();
mre.WaitOne(30000); // waiting 30 secs (or less)
if (actionThread.IsAlive) actionThread.Abort();
}
You can run the method in a separate thread, and monitor it and force it to exit if it works too long. A good way, if you can call it as such, would be to develop an attribute for the method in Post Sharp so the watching code isn't littering your application.
I've written the following as sample code(note the sample code part, it works, but could suffer issues from multithreading, or if the method in question captures the ThreadAbortException would break it):
static void ActualMethodWrapper(Action method, Action callBackMethod)
{
try
{
method.Invoke();
} catch (ThreadAbortException)
{
Console.WriteLine("Method aborted early");
} finally
{
callBackMethod.Invoke();
}
}
static void CallTimedOutMethod(Action method, Action callBackMethod, int milliseconds)
{
new Thread(new ThreadStart(() =>
{
Thread actionThread = new Thread(new ThreadStart(() =>
{
ActualMethodWrapper(method, callBackMethod);
}));
actionThread.Start();
Thread.Sleep(milliseconds);
if (actionThread.IsAlive) actionThread.Abort();
})).Start();
}
With the following invocation:
CallTimedOutMethod(() =>
{
Console.WriteLine("In method");
Thread.Sleep(2000);
Console.WriteLine("Method done");
}, () =>
{
Console.WriteLine("In CallBackMethod");
}, 1000);
I need to work on my code readability.
Methods don't have timeouts in C#, unless your in the debugger or the OS believes your app has 'hung'. Even then processing still continues and as long as you don't kill the application a response is returned and the app continues to work.
Calls to databases can have timeouts.
Could you create an Asynchronous Method so that you can continue doing other stuff whilst the "busy" method completes?
I regularly write apps where I have to synchronize time critical tasks across platforms. If you can avoid thread.abort you should. See http://blogs.msdn.com/b/ericlippert/archive/2010/02/22/should-i-specify-a-timeout.aspx and http://www.interact-sw.co.uk/iangblog/2004/11/12/cancellation for guidelines on when thread.abort is appropriate. Here are the concept I implement:
Selective execution: Only run if a reasonable chance of success exists (based on ability to meet timeout or likelihood of success result relative to other queued items). If you break code into segments and know roughly the expected time between task chunks, you can predict if you should skip any further processing. Total time can be measured by wrapping an object bin tasks with a recursive function for time calculation or by having a controller class that watches workers to know expected wait times.
Selective orphaning: Only wait for return if reasonable chance of success exists. Indexed tasks are run in a managed queue. Tasks that exceed their timeout or risk causing other timeouts are orphaned and a null record is returned in their stead. Longer running tasks can be wrapped in async calls. See example async call wrapper: http://www.vbusers.com/codecsharp/codeget.asp?ThreadID=67&PostID=1
Conditional selection: Similar to selective execution but based on group instead of individual task. If many of your tasks are interconnected such that one success or fail renders additional processing irrelevant, create a flag that is checked before execution begins and again before long running sub-tasks begin. This is especially useful when you are using parallel.for or other such queued concurrency tasks.