Do not use Timers incorrectly

[randem]

Many people are having problems with timers and asking about timers. If you want to use a timer in your app. Please follow these suggestion to help insure that you do not have problems.

1) In VB6, Do not Disable and Re-Enable your timer. This will cause your timer to still run after the program is terminated causing the timer function to still run (unless you disable the timer in your unload code).

Upon entering the timer code use

Private Sub Timer1_Timer()
 
'Add your code here
 
End Sub

2) You can use more than one timer on a form.

Seperate your code into each timer that will interrupt on it own interval. Timers should not be confused with timing functions. A timer will interrupt your code on the set intervals so that you may do other things. Timing functions are called to time the elapsed time between set areas in code or time betwwen events happening.

Following these rules will make sure that your problems are not timer issues.

[Pradeep1210]

Nice thing randem!
I'll like to add
3) Check whether you need a timer at all or not
Timers run in seperate thread. Your code continues to run after enabling the timer. Usually u want to just wait for the timer to finish and then resume your code. In such cases just use loops with DoEvents instead of timers.

[chemicalNova]

You could even go as far as saying, don't use Timers at all. Using GetTickCount is better, and QueryPerformanceCounter is even better. Try for those

chem

[randem]

chemicalNova,

Timers are essential. You can't interrupt running code with GetTickCount. That is the main purpose of timers... To interrupt running code.

You are confusing Timers with Timing.

[hassa046]

Nice post. Very helpful.

[Dave Sell]

Private Sub Timer1_Timer()
Timer1.Enabled = False
 
'Add your code here
 
    Select Case tmrflg
 
        Case (First Condition)
 
        Case (Second Condition)
 
        ....
 
    End Select
 
'and just before exiting the timer code do
 
Timer1.Enabled = True
End Sub

Shouldn't it be?:

Timer1.Enabled = False

[CVMichael]

I really don't understand what's the fuss about timers...

I have an application with about 30 forms, some of the forms have multiple instances while app is running, and ALL forms have at least one timer on each form... have not had ANY problem with the app as of yet regarding timers. Memory is fine, CPU usage is low, I really don't understand why you guys have a problem with timers.

And by the way, this:

Private Sub Timer1_Timer()
Timer1.Enabled = False
 
'Add your code here
 
'and just before exiting the timer code do
Timer1.Enabled = True
End Sub

NEVER HAPENS to interrupt itself !! Did you actually try it ?

A timer never fires again until you exit the current instance... so what's the point of that code ?

[Jacob Roman]

You should never be using Timers to begin with unless you are that desperate on low CPU usage. Timers are slow, inaccurate, and inconsistant. It's even worse on XP computers since they go 10 times faster, making them really inaccurate and inconsistant. And you are right. It's even more worse when having two or more timers run at the same time. Using managed loops with a frame limiter is the way to go for better accuracy. And that loop should be the only loop in your app that'll take care of everything, such as a Game Loop. But that would mean more CPU usage.

[CVMichael]

Anyone wants to prove me wrong with actual proof (code) ??
I know the timer is inacurate, so prove me wrong on other things that you think it's bad about timers...

I'm curious on why everybody is so disapointed about the timer control, cuz I never had any problems with it in my 8 years of programming in VB.

[CVMichael]

First of all, a timer does NOT interrupt (this is not C++ to use interrupts), and the following code proves it !

Option Explicit
 
Private Declare Function GetTickCount Lib "kernel32" () As Long
Private LastTick As Long
 
Private Sub Form_Load()
    LastTick = GetTickCount
    Timer1.Interval = 500
End Sub
 
Private Sub Timer1_Timer()
    Debug.Print "Timer1_Timer: " & GetTickCount - LastTick
    LastTick = GetTickCount
    
    Pause 1 ' pause for one second
End Sub
 
Private Sub Pause(ByVal Interval As Single)
    Dim EndTime As Single
    EndTime = Timer + Interval
    
    Do
        DoEvents
    Loop Until Timer >= EndTime
End Sub

Output:
Timer1_Timer: 500
Timer1_Timer: 1500
Timer1_Timer: 1500
Timer1_Timer: 1500
Timer1_Timer: 1500
Timer1_Timer: 1500
Timer1_Timer: 1500
Timer1_Timer: 1500
Timer1_Timer: 1500
keeps going like this...

What does this prove ?
First of all, if a timer would really Interrupt, then you would get an event EVERY 500 ms, and guess what ? it does not...

This proves that the interval you set in a timer is the time it takes from the time the timer sub ends to the time the sub get's called again. The time spent inside the call is added to the total time (timer's Interval), THEREFORE everyone thinks that a timer is not precise !! and guess what, if you add the 500 ms with the 1 second you will have a total of 1500 ms, from what I see the timer interval takes exactly 1500... hmmm what a coincidence !

It seems that a timer is more precise than I originaly thought...

[randem]

CVMichael,

You are indeed correct. MS must have changed the timers.

[CVMichael]

Thank you... I feel much better now

Any other bad things about timers ?

I can't wait until this "myth" of "timers = bad" ends.

[CVMichael]

That's weird , I thought there was another post between post number 9 and 10... hmmm....

[Jacob Roman]

When using Timers in XP, they are 10 times faster than usual. And GetTickCount is not as accurate. It's only 10 ms accurate. Best to use the QueryPerformanceCounter And the QuerePerformanceFrequency API's for 1 ms accuracy.

[CVMichael]

Hmmm, same code as above, but on my home computer, I get this output:

Timer1_Timer: 501
Timer1_Timer: 1502
Timer1_Timer: 1502
Timer1_Timer: 1502
Timer1_Timer: 1503
Timer1_Timer: 1502

It seems that a timer is more acurate on some comptuers than others...

[CVMichael]

I'm just curious what output do you guys get when you run the following function:

Option Explicit
 
Private Declare Function GetTickCount Lib "kernel32" () As Long
 
Private Sub Form_Load()
    FindTimeAccuracy
End Sub
 
Private Sub FindTimeAccuracy()
    Dim SmallestDiff As Single, PrevTime As Single, CurrTime As Single, K As Long
    Dim CurrTick As Long, PrevTick As Long
    
    PrevTime = Timer
    SmallestDiff = 2 ^ 16
    
    For K = 0 To 1000000
        CurrTime = Timer
        
        If PrevTime <> CurrTime Then
            If CurrTime - PrevTime < SmallestDiff Then SmallestDiff = CurrTime - PrevTime
            
            PrevTime = Timer
        End If
    Next K
    
    Debug.Print "Timer = " & SmallestDiff * 1000 & " ms"
    
    PrevTick = GetTickCount
    SmallestDiff = 2 ^ 16
    
    For K = 0 To 10000000
        CurrTick = GetTickCount
        
        If PrevTick <> CurrTick Then
            If CurrTick - PrevTick < SmallestDiff Then SmallestDiff = CurrTick - PrevTick
            
            PrevTick = GetTickCount
        End If
    Next K
    
    Debug.Print "GetTickCount = " & SmallestDiff & " ms"
End Sub

I get this output:

Timer = 15.625 ms
GetTickCount = 15 ms

What do you get ?

[MorpheusM]

First of all, a timer does NOT interrupt (this is not C++ to use interrupts), and the following code proves it !

Option Explicit
 
Private Declare Function GetTickCount Lib "kernel32" () As Long
Private LastTick As Long
 
Private Sub Form_Load()
    LastTick = GetTickCount
    Timer1.Interval = 500
End Sub
 
Private Sub Timer1_Timer()
    Debug.Print "Timer1_Timer: " & GetTickCount - LastTick
    LastTick = GetTickCount
    
    Pause 1 ' pause for one second
End Sub
 
Private Sub Pause(ByVal Interval As Single)
    Dim EndTime As Single
    EndTime = Timer + Interval
    
    Do
        DoEvents
    Loop Until Timer >= EndTime
End Sub

Output:
Timer1_Timer: 500
Timer1_Timer: 1500
Timer1_Timer: 1500
Timer1_Timer: 1500
Timer1_Timer: 1500
Timer1_Timer: 1500
Timer1_Timer: 1500
Timer1_Timer: 1500
Timer1_Timer: 1500
keeps going like this...

What does this prove ?
First of all, if a timer would really Interrupt, then you would get an event EVERY 500 ms, and guess what ? it does not...

This proves that the interval you set in a timer is the time it takes from the time the timer sub ends to the time the sub get's called again. The time spent inside the call is added to the total time (timer's Interval), THEREFORE everyone thinks that a timer is not precise !! and guess what, if you add the 500 ms with the 1 second you will have a total of 1500 ms, from what I see the timer interval takes exactly 1500... hmmm what a coincidence !

It seems that a timer is more precise than I originaly thought...

Yes you are right! BUT!!! Try bigger or lower values for timer interval. For example - if 10 then relust is:

Timer1_Timer: 16
Timer1_Timer: 1016
Timer1_Timer: 1015
Timer1_Timer: 1016
Timer1_Timer: 1015

and go on...
My CPU is AMD 3000 + with 512 MB RAM

[CVMichael]

I already knew that the timer is not precise. The point I was trying to make is that the timer does not Interrupt. Randem deleted the post where he was stating that timers interrupt... now I look like an fool because of that... He also edited his first post. Now this thread is kinda poitless because there is no good proof for "Do not use Timers incorrectly".


Edit: Edited post language - Hack

[thegreatone]

I'm just curious what output do you guys get when you run the following function:

Option Explicit
 
Private Declare Function GetTickCount Lib "kernel32" () As Long
 
Private Sub Form_Load()
    FindTimeAccuracy
End Sub
 
Private Sub FindTimeAccuracy()
    Dim SmallestDiff As Single, PrevTime As Single, CurrTime As Single, K As Long
    Dim CurrTick As Long, PrevTick As Long
    
    PrevTime = Timer
    SmallestDiff = 2 ^ 16
    
    For K = 0 To 1000000
        CurrTime = Timer
        
        If PrevTime <> CurrTime Then
            If CurrTime - PrevTime < SmallestDiff Then SmallestDiff = CurrTime - PrevTime
            
            PrevTime = Timer
        End If
    Next K
    
    Debug.Print "Timer = " & SmallestDiff * 1000 & " ms"
    
    PrevTick = GetTickCount
    SmallestDiff = 2 ^ 16
    
    For K = 0 To 10000000
        CurrTick = GetTickCount
        
        If PrevTick <> CurrTick Then
            If CurrTick - PrevTick < SmallestDiff Then SmallestDiff = CurrTick - PrevTick
            
            PrevTick = GetTickCount
        End If
    Next K
    
    Debug.Print "GetTickCount = " & SmallestDiff & " ms"
End Sub

I get this output:

Timer = 15.625 ms
GetTickCount = 15 ms

What do you get ?

I also get

Timer = 15.625 ms
GetTickCount = 15 ms