Vista - Are Threading.Timers Supposed to be Accurate?

Perhaps I have misunderstood how these things work. I have a Threading.Timer
object set to go off every 10 seconds. The timer callback sends some data
out on a TCP socket and checks for a reply. It then terminates. It will only
wait for a maximum of 5 seconds, but occasionally it will timeout and exit.

If the first callback occurs at time t and takes 5 seconds to complete, I am
expecting the next callback to occur at t+10. That's correct, isn't it?

What I am finding is that sometimes a callback doesn't occur for as much as
22 seconds after the previous one. What could cause this?

Would a System.Timers.Timer be any better?

TIA

Charles

"Charles" <blank@newsgroup> wrote in message
news:e2gveZpVKHA.1280@newsgroup
I'm not sure how dotnet handles timers, but in the underlying Windows API,
your first scenario simply can't happen (t+5) for a 10 second timer. Your
second scenario can happen in the rare situation where your system is
extremely busy and sluggish. Basically, the Windows Timer (WM_TIMER)
messages are the second lowest priority messages in the system - only the
WM_PAINT message that generates the OnPaint() event is lower and only occurs
if there are no other messages waiting to be processed.

Please post your timer creation code so we can better help.

Mike Ober.

Hi Michael

Thanks for the reply.
I meant that the callback takes 5 seconds to do its work, but below I have
seen teh callback report 5 seconds.

Here's the code

' Create timer
m_Timer = New Threading.Timer(AddressOf TimerCallback, New TimerState,
10000, 10000)

And the TimerCallback function is

Private Sub PollCallback(ByVal state As Object)

SyncLock Me
Try
Dim TimeNow As DateTime = Now

ts = DirectCast(state, TimerState)

If Not ts.FirstTime Then
Dim ElapsedSeconds As Long =
DateDiff(DateInterval.Second, ts.LastCalled, TimeNow)

If ElapsedSeconds < 9 Then
' Called too quickly
OnTimerError(String.Format("Timer Request queued too
quickly, in {0} seconds", ElapsedSeconds))

ElseIf ElapsedSeconds > 11 Then
' Called too slowly
OnTimerError(String.Format("Timer Request queued too
slowly, in {0} seconds", ElapsedSeconds))
End If
End If

ts.LastCalled = TimeNow ' assignment clears FirstTime
flag

' Do stuff that takes 1 to 5 seconds

End SyncLock

End Sub

Sometimes it reports 5 seconds, sometimes 14, sometimes 25. Mostly it
reports nothing.

There are other things going on in the app, but mostly just waiting on wait
handles for things to be signalled, like messages coming in. CPU never gets
abovre a few percent for the whole machine, running Windows Server 2003.

Charles


"Michael D. Ober" <obermd.@newsgroup> wrote in message
news:qs6dnUhCqKw003vXnZ2dnUVZ_uidnZ2d@newsgroup