Timer Events - Visual Basic 4 / 5 / 6

Max

This may be an elementary question but it's something I have not encountered
in about 10 years writing code in VB 5 / 6

I have a timer that using the API checks if there has been a change to one
of several watched directories in the file system, if there has been a
change a rather long running process is started.

The long running process loops through all files comparing the last modified
attributes on each to those in the database if there is a change the
database is updated.

Simple so far right ?

Just prior to the loop statement in that routine there is a DoEvents to keep
everything ticking along, however something interesting happens.

I have another timer on a very short interval watching for something else to
happen. This something else is unrelated to the file system, it is updating
the status of an out of process com component.

This second timer is not firing while the long running process is taking
place, the do events is working because the status of the long running
process is updated in the status bar of the application and that works.

Is there a rule that I have missed that says only one timer event can be
running at any one time ?

Come to think of it over the years I have only ever put very short routines
in timers so have never faced such a problem.

I can think of a few ways to get around this but am wondering if you agree
with my reasoning?

All the best for the new year

Max

Jan 1 '07 #1

Subscribe Reply

7036

Ralph

"Max" <no****@spamcat chers.comwrote in message
news:45******** **************@ news.optusnet.c om.au...

This may be an elementary question but it's something I have not

encountered

in about 10 years writing code in VB 5 / 6

I have a timer that using the API checks if there has been a change to one
of several watched directories in the file system, if there has been a
change a rather long running process is started.

The long running process loops through all files comparing the last

modified

attributes on each to those in the database if there is a change the
database is updated.

Simple so far right ?

Just prior to the loop statement in that routine there is a DoEvents to

keep

everything ticking along, however something interesting happens.

I have another timer on a very short interval watching for something else

happen. This something else is unrelated to the file system, it is

updating

the status of an out of process com component.

This second timer is not firing while the long running process is taking
place, the do events is working because the status of the long running
process is updated in the status bar of the application and that works.

Is there a rule that I have missed that says only one timer event can be
running at any one time ?

Come to think of it over the years I have only ever put very short

routines

in timers so have never faced such a problem.

I can think of a few ways to get around this but am wondering if you agree
with my reasoning?

All the best for the new year

Max

The short answer is no - there is no 'rule' that says you can't have more
than one timer running at a time. However, you can occasionally arrange
things such that you can experience 'unexpected' behavior. <g>

As Timers are not hard interupts and a Timer event has to wait for its turn
to run, just like any other event, a long running process in one timer can
definitely effect results. The usual fix is to install judicious DoEvents in
a long running process - it sounds like you have tried that. You may just
need to do some re-arranging.

Without knowing more about your particular situation I wouldn't venture a
specific solution. But you can take heart that one is likely possible.

As a sidenote: Just in case, be aware that timers act differently when run
in debug mode (in an IDE) than when released. They also can react strangely
with MsgBoxes/Modal dialogs. So do your testing with release versions and
monitor the behavior with logs or DebugOutputStri ng and DebugViewers.

Placing Timers in a Control Array and thus having only one event (point of
entry)can often simplify the coding and make it easier to monitor the
behavior.

At the other end of the spectrum you might consider reworking your
application to using FindFirstChange Notification/FindNextChangeN otification
functions with the WaitForMultiple Objects function, and eliminate one of the
timers entirely.

hth
-ralph

Jan 1 '07 #2

Steve Gerrard

"Max" <no****@spamcat chers.comwrote in message
news:45******** **************@ news.optusnet.c om.au...

>
This second timer is not firing while the long running process is taking
place, the do events is working because the status of the long running process
is updated in the status bar of the application and that works.

I would bet that the second timer is firing with each DoEvents (unless you just
have the code mangled up).

It is more likely that it is is firing, but you are not seeing the out of
process component updated as you expect.

It should be easy to put in a visual queue that the second short timer is indeed
firing during the long loop - a debug statement, a character added to a text box
on a form, whatever works.

You might well find that the issue is more to do with the out of process
component not getting any processing time to update itself, since your app is so
busy when it is in the long loop.

Jan 1 '07 #3

Max

Thanks Ralph

I will look at the re working of the code you have given me some good ideas
there and thanks for the tip on the different behaviour when running in the
IDE.

The app is one that has grown over the past 6 years and could do with a good
rethink.
Max

"Ralph" <nt************ *@yahoo.comwrot e in message
news:Gd******** *************** *******@arkansa s.net...

>
"Max" <no****@spamcat chers.comwrote in message
news:45******** **************@ news.optusnet.c om.au...
>This may be an elementary question but it's something I have not
encountered
>in about 10 years writing code in VB 5 / 6

I have a timer that using the API checks if there has been a change to
one
of several watched directories in the file system, if there has been a
change a rather long running process is started.

The long running process loops through all files comparing the last
modified
>attributes on each to those in the database if there is a change the
database is updated.

Simple so far right ?

Just prior to the loop statement in that routine there is a DoEvents to
keep
>everything ticking along, however something interesting happens.

I have another timer on a very short interval watching for something else
to
>happen. This something else is unrelated to the file system, it is
updating
>the status of an out of process com component.

This second timer is not firing while the long running process is taking
place, the do events is working because the status of the long running
process is updated in the status bar of the application and that works.

Is there a rule that I have missed that says only one timer event can be
running at any one time ?

Come to think of it over the years I have only ever put very short
routines
>in timers so have never faced such a problem.

I can think of a few ways to get around this but am wondering if you
agree
with my reasoning?

All the best for the new year

Max

The short answer is no - there is no 'rule' that says you can't have more
than one timer running at a time. However, you can occasionally arrange
things such that you can experience 'unexpected' behavior. <g>

As Timers are not hard interupts and a Timer event has to wait for its
turn
to run, just like any other event, a long running process in one timer can
definitely effect results. The usual fix is to install judicious DoEvents
in
a long running process - it sounds like you have tried that. You may just
need to do some re-arranging.

Without knowing more about your particular situation I wouldn't venture a
specific solution. But you can take heart that one is likely possible.

As a sidenote: Just in case, be aware that timers act differently when run
in debug mode (in an IDE) than when released. They also can react
strangely
with MsgBoxes/Modal dialogs. So do your testing with release versions and
monitor the behavior with logs or DebugOutputStri ng and DebugViewers.

Placing Timers in a Control Array and thus having only one event (point of
entry)can often simplify the coding and make it easier to monitor the
behavior.

At the other end of the spectrum you might consider reworking your
application to using
FindFirstChange Notification/FindNextChangeN otification
functions with the WaitForMultiple Objects function, and eliminate one of
the
timers entirely.

hth
-ralph

Jan 1 '07 #4

Max

Thanks Steve,

I had a break in the 2nd timer event that was not being hit but I will do
the visual test. and run it as an EXE

The out of process component is media player and the audio is playing
without a hiccup however your suggestion my be correct it that its not
returning it's position because there is no processor time.

All the best
Max

"Steve Gerrard" <my********@com cast.netwrote in message
news:0O******** *************** *******@comcast .com...

>
"Max" <no****@spamcat chers.comwrote in message
news:45******** **************@ news.optusnet.c om.au...
>>
This second timer is not firing while the long running process is taking
place, the do events is working because the status of the long running
process is updated in the status bar of the application and that works.

I would bet that the second timer is firing with each DoEvents (unless you
just have the code mangled up).

It is more likely that it is is firing, but you are not seeing the out of
process component updated as you expect.

It should be easy to put in a visual queue that the second short timer is
indeed firing during the long loop - a debug statement, a character added
to a text box on a form, whatever works.

You might well find that the issue is more to do with the out of process
component not getting any processing time to update itself, since your app
is so busy when it is in the long loop.

Jan 1 '07 #5

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