DoEvents Overhead 1

[Error7]

I have been experimenting with DoEvents to allow the user to cancel processing of the following code.

Without using DoEvents the process takes 1 min 27 sec.
With DoEvents in the outer loop as shown, it takes 3 min 1 sec.

But if I Rem out the first DoEvents and un-rem the second the process takes a whopping 8 min 45 secs.

For a = 0 To cmbSites.ListCount - 1
DoEvents
If CancelErr Then Exit For
Open App.Path & "\" & IP(a) & ".txt" For Output As #2
For i = 0 To lstCsvfiles.ListCount - 1
StatusBar1.Panels(1).Text = "Scanning " & lstCsvfiles.List(i) & " for " & IP(a)
Open lstCsvfiles.List(i) For Input As #1
Do While Not EOF(1)
'DoEvents
'If CancelErr Then Exit For
Line Input #1, FileString
If InStr(FileString, IP(a)) Then
Print #2, FileString
End If
Loop
Close #1
Next i
Close #2
Next a

Is there a more efficient way of allowing the user to cancel a process?

Alan

[gray]Experience is something you don't get until just after you need it.[/gray]

 

[strongm]

>a whopping 8 min 45 secs

And this is just one of the reasons that you will find a number of us in here advising against the use of DoEvents if it can be avoided ...

 

[PatrickIRL]

I seem to recall that there is (was??) an API that can be used instead which is less intrusive. For the life of me I can't remember it though.

I'm sure there's many here who will point you in the right direction.

Patrick

 

[Swi]

Only use DoEvents every x amount of records.

Dim x as Long

For x = 0 To 5000000
If x Mod 1500 Then DoEvents
If CancelErr Then Exit For
Next

Swi

 

[Error7]

Thanks Patrick.

I would like to include a cancel option at some point in the loops because the times I provided earlier are from a partial run of the process.

A complete run is likely to take some considerable time even without DoEvents.

Alan

[gray]Experience is something you don't get until just after you need it.[/gray]

 

[Error7]

Thanks Swi

Effectively that is what I am doing here:

For a = 0 To cmbSites.ListCount - 1
DoEvents

Alan

[gray]Experience is something you don't get until just after you need it.[/gray]

 

[PatrickIRL]

Just had a look and found this...

http://www.vbcity.com/forums/topic.asp?tid=8585

There's a discussion on using the GetInputState API which sounds familiar.

Patrick

 

[strongm]

Oh, I wouldn't necessarily go with GetInputState either.

I was going to post a suggestion that you consider a PeekMessage/TranslateMessage/DispatchMessage solution - but see that the thread redsmooth provides covers this

 

[PatrickIRL]

I didn't test the code that was there but why wouldn't you recommend GetInputState??

 

[strongm]

OK - what would you do if GetInputState returned a nonzero value?

i.e how would you deal with there being a pending message in the moue/keyboard input queue?

 

[PatrickIRL]

I found some more info here (

http://www.kbalertz.com/kb_35605.aspx)

and Ok, after another look I see what you're getting at.

 

[TheVampire]

How about using GetAsyncKeyState instead? This doesn't read the buffer, only if the key is currently being held down. Use a function key and check to see if it is down. If it is, exit the routine.

Robert

 

[Error7]

Thank you Robert.

GetAsyncKeyState was easy to implement and doesn't appear to have any measureable overhead.

Alan

[gray]Experience is something you don't get until just after you need it.[/gray]

 

[strongm]

>GetAsyncKeyState

One drawback of the above:

Given that the process takes, by your reckoning, 1 min 27 seconds to run it is entirely possible that the user might switch to another application. So what happens then?

 

[Error7]

Thanks strongm, and thanks for your earlier input.

I was aware that this might be a problem in general practice but it is unlikely to occur in this particular application.

Alan

[gray]Experience is something you don't get until just after you need it.[/gray]

 

[TheVampire]

And if you were concerned about it occuring, you could put a test in your code to see if your application had focus or not. If it doesn't have focus, it would ignore ( or not even check ) the GetAsyncKeyState.

Robert

 

[Error7]

Thanks Robert, I will add that to my app.

Alan

[gray]Experience is something you don't get until just after you need it.[/gray]