How can i implement a message pump with winforms ?

[nicolas.hilaire]

Hi all,

i'm doing a quite long treatment in a function, and i'm showing the
progress of the treatment with a progressbar. The code is something
like this :

for each(entry in entries) // about 100 entries
{
TreatmentForOne Or2Secs();
this->progressBar1->PerformStep( );
}
during the debug, the debugger tells me that :

Managed Debugging Assistant 'ContextSwitchD eadlock' has detected a
problem in 'd:\test\NetSen dDotNet\debug\N etSendDotNet.ex e'.
Additional Information: The CLR has been unable to transition from COM
context 0x189558 to COM context 0x189408 for 60 seconds. The thread
that owns the destination context/apartment is most likely either doing
a non pumping wait or processing a very long running operation without
pumping Windows messages. This situation generally has a negative
performance impact and may even lead to the application becoming non
responsive or memory usage accumulating continually over time. To avoid
this problem, all single threaded apartment (STA) threads should use
pumping wait primitives (such as CoWaitForMultip leHandles) and
routinely pump messages during long running operations.
Specially :
To avoid this problem, all single threaded apartment (STA) threads
should use pumping wait primitives (such as CoWaitForMultip leHandles)
and routinely pump messages during long running operations.

So, how can i pumping messages ? or, should i use a thread (and how ?)
Thanks for your help
Nicolas H.

[nicolas.hilaire]

ok, i've tried this, but this is not working, as if the window is
frozen

I'm using ThreadPool and ManualResetEven t in my form class

Is this way of doing not good ?
System::Collect ions::ArrayList ^ getList()
{
list = gcnew System::Collect ions::ArrayList ();
manualEvent = gcnew System::Threadi ng::ManualReset Event(false);
System::Threadi ng::ThreadPool: :QueueUserWorkI tem(gcnew
System::Threadi ng::WaitCallbac k(this,
&myNameSpace::f rm_loading::Thr eadProcess));
manualEvent->WaitOne();
return list;
}

void ThreadProcess(S ystem::Object ^ stateInfo)
{
manualEvent->Reset();

this->progressBar1->Minimum = 0;
this->progressBar1->Maximum = nb;
this->progressBar1->Value = 0;
this->progressBar1->Step = 1;
this->Show();
this->Update();

for each (entry in entries)
{
TreatmentLongOn Entry();
this->progressBar1->PerformStep( );
}
this->Hide();
manualEvent->Set();
}
How can i correct ?

Thanks in advance

Best regards,

Nicolas

[Willy Denoyette [MVP]]

<ni************ *@motorola.com> wrote in message
news:11******** *************@g 44g2000cwa.goog legroups.com...
| >That means you are running your long running task on the UI thread, this
is
| >something you should not do, run this on another thread and call Invoke
or
| >BeginInvoke to update the progressBar, that way your UI will remain
| >responsive.
|
| Yes, i'm running the task on the form class.
|
| So, i'm going to use thread ... but, i just need something easy
|
| something like this
|
| Thread ^ t = gcnew Thread(gcnew ThreadStart(Thr eadProcess));
| t->Start();
| WaitForTheThrea dToTerminate();
|
| Is this possible ? and how ?
|
|
| Thanks for your help
|
I would suggest you take some time to read the docs before you start using
multiple threads.
Anyway here is how you could init a background thread, probaly you must
initialize him to enter the STA as you seem to call into COM in your "task".

// in some handler (button click ??)

Thread ^ t = gcnew Thread(gcnew ThreadStart(thi s->MyLongRunningT ask));
t.SetApartmentS tate = ApartmentState. STA; // see above
t.IsBackground = true;
t->Start();
// no need to wait for the thread to terminate!!
....
void MyLongRunningTa sk()
{
// keep the busy

}
Willy.

[nicolas.hilaire]

>I would suggest you take some time to read the docs before you start using

multiple threads.
Anyway here is how you could init a background thread, probaly you must
initialize him to enter the STA as you seem to call into COM in your "task". // in some handler (button click ??) Thread ^ t = gcnew Thread(gcnew ThreadStart(thi s->MyLongRunningT ask));
t.SetApartmentS tate = ApartmentState. STA; // see above
t.IsBackground = true;
t->Start();
// no need to wait for the thread to terminate!!
... void MyLongRunningTa sk()
{
// keep the busy

}

Thanks for your help,

In fact, i need to wait for the thread to finish, because, as you can
see in my last post, i'm returning a list, that is built in the
longTask function.

Regards

[Willy Denoyette [MVP]]

<ni************ *@motorola.com> wrote in message
news:11******** *************@g 43g2000cwa.goog legroups.com...
| >I would suggest you take some time to read the docs before you start
using
| >multiple threads.
| >Anyway here is how you could init a background thread, probaly you must
| >initialize him to enter the STA as you seem to call into COM in your
"task".
|
| >// in some handler (button click ??)
|
| > Thread ^ t = gcnew Thread(gcnew ThreadStart(thi s->MyLongRunningT ask));
| > t.SetApartmentS tate = ApartmentState. STA; // see above
| > t.IsBackground = true;
| > t->Start();
| >// no need to wait for the thread to terminate!!
| >...
|
| >void MyLongRunningTa sk()
| >{
| >// keep the busy
| >
| >}
|
| Thanks for your help,
|
| In fact, i need to wait for the thread to finish, because, as you can
| see in my last post, i'm returning a list, that is built in the
| longTask function.
|
| Regards
|

No, Waiting on a UI thread means rendering the UI non-responsive. I guess
you need the list to update the UI, well do this from the non UI thread
using Control->Invoke or BeginInvoke.

Willy.

[nicolas.hilaire]

>No, Waiting on a UI thread means rendering the UI non-responsive. I guess

you need the list to update the UI, well do this from the non UI thread
using Control->Invoke or BeginInvoke.

Hi again and thanks for your answer. I tryed to implement the method
using BeginInvoke. But, the UI is still quite frozen (my progressbar is
refreshing, but the entire form is not). And when i put an other
application on top of the z-order, i can't go back to my window, during
the long task.

This is my code, i hope you can find why it's not working (I'm calling
the method getList(), that constructs a list, shows a form with a
progress bar during the construction, and returns me the list at the
end)
System::Collect ions::ArrayList ^ getList ()
{
list = gcnew System::Collect ions::ArrayList ();
int nb = 40;
this->progressBar1->Visible = true;
this->progressBar1->Minimum = 0;
this->progressBar1->Maximum = nb;
this->progressBar1->Value = 0;
this->progressBar1->Step = 1;
this->Show();
this->Update();
System::IAsyncR esult ^ res;

res = this->BeginInvoke(gc new InvokeMethod(th is,
&myProject::frm _loading::Updat eProgressBar), nullptr);
this->EndInvoke(res) ;
System::Threadi ng::Thread::Sle ep(1000);
this->Hide();

return list;
}

private:
void UpdateProgressB ar(void)
{

for (int i=0;i<40;i++)
{
list->Add(System::Co nvert::ToString (i));
this->progressBar1->PerformStep( );
System::Threadi ng::Thread::Sle ep(500);
}

}
Thanks a lot in advance

[Willy Denoyette [MVP]]

I don't see any thread creation in the code you posted, is getList() your
thread procedure?
Also, you don't need to call EndInvoke after a BeginInvoke call. I also
don't get why you are calling Sleep either.

Willy.
<ni************ *@motorola.com> wrote in message
news:11******** **************@ g43g2000cwa.goo glegroups.com.. .
| >No, Waiting on a UI thread means rendering the UI non-responsive. I guess
| >you need the list to update the UI, well do this from the non UI thread
| >using Control->Invoke or BeginInvoke.
|
| Hi again and thanks for your answer. I tryed to implement the method
| using BeginInvoke. But, the UI is still quite frozen (my progressbar is
| refreshing, but the entire form is not). And when i put an other
| application on top of the z-order, i can't go back to my window, during
| the long task.
|
| This is my code, i hope you can find why it's not working (I'm calling
| the method getList(), that constructs a list, shows a form with a
| progress bar during the construction, and returns me the list at the
| end)
|
|
| System::Collect ions::ArrayList ^ getList ()
| {
| list = gcnew System::Collect ions::ArrayList ();
| int nb = 40;
| this->progressBar1->Visible = true;
| this->progressBar1->Minimum = 0;
| this->progressBar1->Maximum = nb;
| this->progressBar1->Value = 0;
| this->progressBar1->Step = 1;
| this->Show();
| this->Update();
| System::IAsyncR esult ^ res;
|
| res = this->BeginInvoke(gc new InvokeMethod(th is,
| &myProject::frm _loading::Updat eProgressBar), nullptr);
| this->EndInvoke(res) ;
| System::Threadi ng::Thread::Sle ep(1000);
| this->Hide();
|
| return list;
| }
|
| private:
| void UpdateProgressB ar(void)
| {
|
| for (int i=0;i<40;i++)
| {
| list->Add(System::Co nvert::ToString (i));
| this->progressBar1->PerformStep( );
| System::Threadi ng::Thread::Sle ep(500);
| }
|
| }
|
|
| Thanks a lot in advance
|

[nicolas.hilaire]

>I don't see any thread creation in the code you posted, is getList() your

thread procedure?
Also, you don't need to call EndInvoke after a BeginInvoke call. I also
don't get why you are calling Sleep either. Willy.

Thanks again for helping me Willy,

I finally changed my way of doing this.

I use the ability of a form to be modal (by calling ShowDialog instead
of Show), then i don't have to care about waiting for the end of the
task.

I'm doing the init in the form_load, then i start a thread, that
perform the long task and update the UI.

At the end of the thread, i'm calling the method close() of the form,
then i came back just after the ShowDialog and i'm getting the list
from the form.
I suppose i can do this, because i didn't dispose the ressources of the
form, right ?
This is now working,
thanks a lot for your help.
Best regards,
Nicolas

[taylorjonl]

ni************* @motorola.com wrote:

*>I don't see any thread creation in the code you posted, is
getList() your

thread procedure?
Also, you don't need to call EndInvoke after a BeginInvoke call. I

also

don't get why you are calling Sleep either.

Willy.

Thanks again for helping me Willy,

I finally changed my way of doing this.

I use the ability of a form to be modal (by calling ShowDialog
instead
of Show), then i don't have to care about waiting for the end of the
task.

I'm doing the init in the form_load, then i start a thread, that
perform the long task and update the UI.

At the end of the thread, i'm calling the method close() of the
form,
then i came back just after the ShowDialog and i'm getting the list
from the form.
I suppose i can do this, because i didn't dispose the ressources of
the
form, right ?
This is now working,
thanks a lot for your help.
Best regards,
Nicolas *

I know this is old but it came up in my googling and figured I would
finish it off in case anyone reads it and doesn't understand.

I think the OP is missing the concept of not blocking a UI thread. I
will try to straighten it out.

When you register for a UI event, such as a button's click event, you
don't want to do any operations that are long, and you don't want to
block(sleep,pau se, wait) in that function. The reason is that this
callback was performed on the UI's main thread and the UI will not
respond during this time. Instead you should create a worker thread.
I will post some code below, it will be in C# since that is my most
familiar language.
Code:
--------------------
public void OnButtonClick( object sender, EventArgs args )
{
Thread.Sleep( 10000 ); <---- BAD, Blocking UI thread
SuperLongCPUInt ensiveCall(); <---- BAD, Blocking UI thread
}
--------------------
The above is bad, and will block UI events. Instead you should create
a call that will run on a thread in the background.
Code:
--------------------
public void OnButtonClick( object sender, EventArgs args )
{
new Thread( SuperLongCPUInt ensiveCall() ).Start();
}
--------------------
The OP was doing the following.
Code:
--------------------
public void OnButtonClick( object sender, EventArgs args )
{
new Thread( SuperLongCPUInt ensiveCall() ).Start();
manualEvent.Wai tOne();
}

public void SuperLongCPUInt ensiveCall()
{
manualEvent.Res et();
// DO A TON OF WORK
manualEvent.Set ();
}
--------------------
That is the same as making the call on the UI thread, actually it is
slower, you are still blocking the UI thread. If you have to define an
additional function that will be started on a background thread then do
it, just don't ever do CPU intensive or blocking calls on a UI thread.

--
taylorjonl
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