CPU USAGE Control.

[ajay_vb]

Hi friends,
Can anybody tell me the programming factors in vb6 or in general, to control the CPU usage. Basically I wanted to limit the program's CPU usage. So can anybody provide appropriate links or useful hints to control CPU usage?
Thanks in advance.
With Regards,
AJAY.

[Pradeep1210]

A normal vb program would rarely consume more than 2 - 3% of the CPU unless something is wrong there.
The most common cause of high CPU usage I have found is doing something in a loop without a DoEvents at appropriate intervals. DoEvents basically processes the system message queue and gives time to your other processes to run.

So, if this is the case with you I suggest you put a DoEvents call inside the loop and see if it drops the CPU usage.

[deathfxu]

Never use DoEvents. Throw this into a module and "Call MyDoEvents":

Private Type POINTAPI
 x As Long
 y As Long
End Type
 
Private Type MSG
 hWnd As Long   'the window handle of the app
 message As Long  'the type of message (e.g. keydown)
 wParam As Long  'the key code
 lParam As Long  'not used
 time As Long   'time when message posted
 pt As POINTAPI  'coordinate of mouse pointer
End Type
 
Private Declare Function PeekMessage Lib "user32" Alias "PeekMessageA" _
(lpMsg As MSG, ByVal hWnd As Long, ByVal wMsgFilterMin As Long, _
ByVal wMsgFilterMax As Long, ByVal wRemoveMsg As Long) As Long
Private Declare Function TranslateMessage Lib "user32" _
(lpMsg As MSG) As Long
Private Declare Function DispatchMessage Lib "user32" Alias "DispatchMessageA" _
(lpMsg As MSG) As Long
 
Private Const PM_REMOVE = &H1
 
'The alternative function for DoEvents:
Public Sub MyDoEvents()
    Dim CurrMsg         As MSG
 
    'The following loop extract all messages from the queue and dispatch them
    'to the appropriate window.
    Do Until PeekMessage(CurrMsg, 0, 0, 0, PM_REMOVE) = 0
        TranslateMessage CurrMsg
        DispatchMessage CurrMsg
    Loop
End Sub

[ajay_vb]

Thanks Mr.Pradeep for your valuable suggestion. Also Thanks Mr.Deathfxu for your codebit. But can you please give the reason for why we should never use DoEvents?Can you be bit more clear about this?Thanking you,
With Regards,
Ajay.

[Pradeep1210]

Thanks Mr.Pradeep for your valuable suggestion. Also Thanks Mr.Deathfxu for your codebit. But can you please give the reason for why we should never use DoEvents?Can you be bit more clear about this?Thanking you,
With Regards,
Ajay.

It would be wrong to say "never use DoEvents". Instead you would almost always use the DoEvents, unless the speed of the code is too much of a concern for your program, since the API version is much faster than the regular DoEvents. Though overuse of DoEvents might slowdown your program. It depends on your specific needs. However, beware of the pitfalls.
Deathfxu seems to have been inspired by this thread, which I had created sometime back to compare the two things.
http://www.vbforums.com/showthread.php?t=365050
I think it might be worth reading for you.

[deathfxu]

Egad, 2005. Never saw that, but that is precisely what I was referring to. :P

The code bit above is just faster. If your program is slower and doesn't really need optimization, like Pradeep said, it's not really necessary.

Just good coding practice.