Delegates and exceptions

**Fred Mellender** · Nov 15 '05, 01:11 PM

Re: Delegates and exceptions

I believe the problem is that the timer and its timeout function run on a
separate thread from the one that started the timer up (see the help page on
Threading.Timer ). Because there is no way to specify an exception handler
on that (system created) thread, you cannot catch an exception thrown in the
timeout thread. If possible you might try to place your exception-catch
logic in the timeout function itself.

Perhaps another way:

Have a separate thread ("controller ") start the "calculator " on its on
thread. Then in controller, do a
calculator.Join (TimeSpan). In statements following the Join, the
controller can check to see that the calculator thread has completed
normally (via Thread.IsAlive, or a bool set by calculator itself). If not,
controller can put out a message, kill calculator, or do another join to
give it more time.

"Pietje de kort" <woutervu@hotma il.com> wrote in message
news:e09cc77a.0 310140314.9cd7c 4a@posting.goog le.com...[color=blue]
> Hello all,
>
> I want to implement Timeout behaviour in a class of mine. When a
> method is called it should timeout after a few seconds. To do this
> I've built a
> System.Threadin g.Timer that calls a delegate method after x milli's,
> the called
> delegate throws an exception indicating timeout.
> The big problem is my code will not catch the thrown exception because
> it
> is generated outside of normal program control. Is there any way to
> catch the
> exception thrown (other than hooking the UncaughtExcepti on event)?
>
> Best regards Wouter
>
> using System.Threadin g;
>
> public class Test
> {
> public Test(){};
>
> public DoTimeoutAction ()
> {
> Timer timer = new Timer(new TimerCallback(T imedout),null,
> 1000,Timeout.In finite);
> Console.WriteLi ne("Doing something");
> Thread.Sleep(50 00); // will cause timeout to occur
> Console.WriteLi ne("Done doing something");
> timer.Dispose() ; // stop timer
> }
>
> private void Timedout(object state)
> {
> throw new ApplicationExce ption("Timeout occured.");
> }
>
> static void Main()
> {
> Test t = new Test();
> try
> {
> t.DoTimeoutActi on();
> }catch(Applicat ionException e)
> {
> Console.WriteLi ne(e.Message);
> }
> Console.WriteLi ne("Done!");
> Console.ReadLin e();
> }
> }[/color]

**Nicholas Paldino [.NET/C# MVP]** · Nov 15 '05, 01:11 PM

Re: Delegates and exceptions

Pietje,

You have to go about this the opposite way actually. The first thing
you need to do is indicate somewhere if the operation completed or not. You
can use a boolean flag for this. Once you have that, you should expose it
as a property (public or private, it is up to you). You need to place a
lock section around the access of this variable.

After that, in your method, you call your operation asynchronously in
another thread (through the thread pool or a separate thread). In the code
that is performing the work, when complete, set the flag to true.

In the code that calls out to the other thread, after the asynchronous
call is made, you can call the static Sleep method to sleep for the amount
of time you want to wait. If the flag is not set when execution resumes,
you can throw your exception.

Of course, this means that if your operation completes, you have to wait
the same amount of time. In order to get around this, replace the boolean
flag with a WaitHandle, such as an event. In your operation, instead of
setting the boolean flag, set the Event. Also, instead of having the thread
put to sleep, you wait on the handle. Before you wait on the handle, you
set your timer to call back a method and set the event when it calls back.
The flag comes in useful here in the timer method, where you will set it to
true. This way, when the call to WaitOne on the Event is complete, you will
know if it timed out or not.

Hope this helps.

"Pietje de kort" <woutervu@hotma il.com> wrote in message
news:e09cc77a.0 310140314.9cd7c 4a@posting.goog le.com...[color=blue]
> Hello all,
>
> I want to implement Timeout behaviour in a class of mine. When a
> method is called it should timeout after a few seconds. To do this
> I've built a
> System.Threadin g.Timer that calls a delegate method after x milli's,
> the called
> delegate throws an exception indicating timeout.
> The big problem is my code will not catch the thrown exception because
> it
> is generated outside of normal program control. Is there any way to
> catch the
> exception thrown (other than hooking the UncaughtExcepti on event)?
>
> Best regards Wouter
>
> using System.Threadin g;
>
> public class Test
> {
> public Test(){};
>
> public DoTimeoutAction ()
> {
> Timer timer = new Timer(new TimerCallback(T imedout),null,
> 1000,Timeout.In finite);
> Console.WriteLi ne("Doing something");
> Thread.Sleep(50 00); // will cause timeout to occur
> Console.WriteLi ne("Done doing something");
> timer.Dispose() ; // stop timer
> }
>
> private void Timedout(object state)
> {
> throw new ApplicationExce ption("Timeout occured.");
> }
>
> static void Main()
> {
> Test t = new Test();
> try
> {
> t.DoTimeoutActi on();
> }catch(Applicat ionException e)
> {
> Console.WriteLi ne(e.Message);
> }
> Console.WriteLi ne("Done!");
> Console.ReadLin e();
> }
> }[/color]

**Pietje de kort** · Nov 15 '05, 01:12 PM

Re: Delegates and exceptions

Hi Nicholas,

that's exactly what I found on some MSDN site!
Here's my example code. The actual work is done
in the DoAction method which signals it's done.

Best regards, Wouter van Vugt (not pietje ;) )

using System;
using System.Collecti ons;

using System.IO;
using System.Threadin g;

namespace TestApp
{
public class TimeoutTest
{
private AutoResetEvent autoEvent;
private int timeout;

public TimeoutTest(int timeout)
{
this.timeout = timeout;
this.autoEvent = new AutoResetEvent( false);
}

public void DoTimeoutAction ()
{
Console.WriteLi ne("Delegating request to work item.");
ThreadPool.Queu eUserWorkItem(n ew WaitCallback(Do Action),null);
Console.WriteLi ne("Waiting for work item to complete.");
int index = WaitHandle.Wait Any(new AutoResetEvent[]{autoEvent},tim eout,false);

if (index == WaitHandle.Wait Timeout)
throw new ApplicationExce ption("Timedout ");
Console.WriteLi ne("Work item completed!");
}

private void DoAction(object state)
{
Console.WriteLi ne("DL Doing Work...");
Thread.Sleep(50 00);
Console.WriteLi ne("DL Done doing work.");
autoEvent.Set() ;
}

static void Main()
{
try
{
TimeoutTest t = new TimeoutTest(100 00);
t.DoTimeoutActi on();
}
catch(Applicati onException e)
{
Console.WriteLi ne(e.Message);
}
Console.ReadLin e();
}
}
}

"Nicholas Paldino [.NET/C# MVP]" <mvp@spam.guard .caspershouse.c om> wrote in message news:<usp7XFlkD HA.2456@TK2MSFT NGP09.phx.gbl>. ..[color=blue]
> Pietje,
>
> You have to go about this the opposite way actually. The first thing
> you need to do is indicate somewhere if the operation completed or not. You
> can use a boolean flag for this. Once you have that, you should expose it
> as a property (public or private, it is up to you). You need to place a
> lock section around the access of this variable.
>
> After that, in your method, you call your operation asynchronously in
> another thread (through the thread pool or a separate thread). In the code
> that is performing the work, when complete, set the flag to true.
>
> In the code that calls out to the other thread, after the asynchronous
> call is made, you can call the static Sleep method to sleep for the amount
> of time you want to wait. If the flag is not set when execution resumes,
> you can throw your exception.
>
> Of course, this means that if your operation completes, you have to wait
> the same amount of time. In order to get around this, replace the boolean
> flag with a WaitHandle, such as an event. In your operation, instead of
> setting the boolean flag, set the Event. Also, instead of having the thread
> put to sleep, you wait on the handle. Before you wait on the handle, you
> set your timer to call back a method and set the event when it calls back.
> The flag comes in useful here in the timer method, where you will set it to
> true. This way, when the call to WaitOne on the Event is complete, you will
> know if it timed out or not.
>
> Hope this helps.
>
>
> "Pietje de kort" <woutervu@hotma il.com> wrote in message
> news:e09cc77a.0 310140314.9cd7c 4a@posting.goog le.com...[color=green]
> > Hello all,
> >
> > I want to implement Timeout behaviour in a class of mine. When a
> > method is called it should timeout after a few seconds. To do this
> > I've built a
> > System.Threadin g.Timer that calls a delegate method after x milli's,
> > the called
> > delegate throws an exception indicating timeout.
> > The big problem is my code will not catch the thrown exception because
> > it
> > is generated outside of normal program control. Is there any way to
> > catch the
> > exception thrown (other than hooking the UncaughtExcepti on event)?
> >
> > Best regards Wouter
> >
> > using System.Threadin g;
> >
> > public class Test
> > {
> > public Test(){};
> >
> > public DoTimeoutAction ()
> > {
> > Timer timer = new Timer(new TimerCallback(T imedout),null,
> > 1000,Timeout.In finite);
> > Console.WriteLi ne("Doing something");
> > Thread.Sleep(50 00); // will cause timeout to occur
> > Console.WriteLi ne("Done doing something");
> > timer.Dispose() ; // stop timer
> > }
> >
> > private void Timedout(object state)
> > {
> > throw new ApplicationExce ption("Timeout occured.");
> > }
> >
> > static void Main()
> > {
> > Test t = new Test();
> > try
> > {
> > t.DoTimeoutActi on();
> > }catch(Applicat ionException e)
> > {
> > Console.WriteLi ne(e.Message);
> > }
> > Console.WriteLi ne("Done!");
> > Console.ReadLin e();
> > }
> > }[/color][/color]

Delegates and exceptions

Delegates and exceptions

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