Hi.

I have a desktop app using Dbisam4 where I would like to perform a backup
when last user closed the application.

Can I use some of the already built in functions of Dbisam to detect wheter
the running application is the last user (session) connected to the
database?

I know that I can run the Dbisam backup at any time, but this is to avoid
every user being asked for backup when closing the application.

Regards
Petter Topp

Petter


File server or client server?

Roy Lambert

Hi Roy.

File server

Petter

"Roy Lambert" <roy.lambert@skynet.co.uk> skrev i melding
news:8CB66CA2-B8B0-43AC-94AA-F3059E5BF383@news.elevatesoft.com...
> Petter
>
>
> File server or client server?
>
> Roy Lambert
>

Peter

It does not matter if you are using C/S or F/S because you can use this
simple approach:

Try to open the tables in exclusive mode, if you can get it, them you are
"alone" in the application and therefore you can backup your data.

Eduardo

Petter


Four approaches that you could take:

1. try and open a table that would be open whenever a user starts your app in exclusive mode. If you can do it you've cracked it - quick close it and start the backup.

2. try starting the backup in the onclose event after closing the tables. Since it requires exclusive access it will only work if no one else is using the tables. Remember to trap the exception.

3. look in the elevatedb.extension ng grab Terry Swires usercount code, modify it for DBISAM and log users on/off properly

4. somewhere in the binaries there should still be an example Tim posted using semaphore flags. As long as there are less than (I think) 255 users then you can set a semaphore as a user logs on, clear it when they log off (I think it happens automagically) and when you want to test for if you should backup try setting all the semaphore flags. Be warned this will take a bit of time

Roy Lambert [Team Elevate]

Petter,

<< Can I use some of the already built in functions of Dbisam to detect
wheter the running application is the last user (session) connected to the
database? >>

Yes, you can use the semaphore locks in DBISAM to do this:

http://www.elevatesoft.com/manual?action=mancompmethod&id=dbisam4&product=d&version=7&comp=TDBISAMTable&method=LockSemaphore

http://www.elevatesoft.com/manual?action=mancompmethod&id=dbisam4&product=d&version=7&comp=TDBISAMTable&method=UnlockSemaphore

Just have each application lock a specific semaphore "slot" when the
application starts up by walking the range of semaphores, and then have the
backup try to lock all semaphores by walking the entire range of slots up
until the maximum number of expected users.

Application code:

CurrentSlot:=1;
while (not LockSemaphore(CurrentSlot)) do
   Inc(CurrentSlot);

Backup code:

CurrentSlot:=1;
while (CurrentSlot <= MaxUsers) do
   begin
   while (not LockSemaphore(CurrentSlot)) do
        Sleep(20);  << Use whatever value you want here
   Inc(CurrentSlot);
   end;

--
Tim Young
Elevate Software
www.elevatesoft.com

"Tim Young [Elevate Software]" <timyoung@elevatesoft.com> wrote in message
news:9625C47D-5EBA-4845-8F80-28209509717E@news.elevatesoft.com...
>
> Backup code:
>
> CurrentSlot:=1;
> while (CurrentSlot <= MaxUsers) do
>    begin
>    while (not LockSemaphore(CurrentSlot)) do
>         Sleep(20);  << Use whatever value you want here
>    Inc(CurrentSlot);
>    end;
>

function NumberOfUsers : integer;
CurrentSlot := 1;
Result := 0;
while CurrentSlot <= MaxUsers do
begin
if LockSemaphore(CurrentSlot) then begin
Sleep(20);
UnlockSemaphore;
end else Result := Result + 1;
inc(CurrentSlot);
end;

that way you don't leave any semaphores set

if NumberOfUsers = 1 then backup else whatever

Robert

Great help guys.

I have plenty to work with.

Have a nice weekend.
Petter

"Petter Topp" <petter.topp@atcdata.no> skrev i melding
news:07411317-F512-4877-A479-B97E079A8D49@news.elevatesoft.com...
> Hi.
>
> I have a desktop app using Dbisam4 where I would like to perform a backup
> when last user closed the application.
>
> Can I use some of the already built in functions of Dbisam to detect
> wheter the running application is the last user (session) connected to the
> database?
>
> I know that I can run the Dbisam backup at any time, but this is to avoid
> every user being asked for backup when closing the application.
>
> Regards
> Petter Topp
>
>

Robert,

<< that way you don't leave any semaphores set >>

Yes, but what I was going for was having the Backup procedure lock all
available slots so that an application cannot start up during the backup and
acquire a slot.

--
Tim Young
Elevate Software
www.elevatesoft.com