[fpc-pascal] Daemon using TTimer on Windows

[Marcos Douglas B. Santos]

On Sat, Jun 30, 2018 at 9:13 PM, R0b0t1 <r030t1 at gmail.com> wrote:
> On Sat, Jun 30, 2018 at 3:57 PM, Marcos Douglas B. Santos
> <md at delfire.net> wrote:
>> Hi,
>>
>> I need to build a daemon app on Windows. It will need a timer to
>> performe some tasks. This timer could be big among 15 min, 30 min, 2
>> hours, etc.
>>
>> I thought that I can use TTimer but I've always heard that it's not
>> possible because some problems related with "NoGUI" stuff.
>>
>> I've found a thread[1] which talks about that but they haven't
>> provided a real solution, at least for Windows.
>>
>> My question is: Nowadays, can I use TTimer with no restrictions in a
>> daemon application on Windows? If not, which could be a possible
>> solution?
>>
>
> If all your service does is wait for the timer you should instead use
> a scheduled task.

Actually, it could be a better idea. I will check the requirements and
think if this would be possible.

> Anyway - does TTimer use the WM_TIMER message? That is the type tied
> to the GUI. Even if you need to use WM_TIMER for some reason you can,
> as services should be run in "session 0" and should have access to a
> GUI. The latter is, I think, a compatibility option you can enable.

I didn't understand this "session 0"... is it a something related to
Lazarus or Windows?

> If you are not opposed to OS-level primitives you should use waitable
> timers (https://docs.microsoft.com/en-us/windows/desktop/sync/using-waitable-timer-objects).
> Using waitable timers you can also wake the computer from sleep.

I'm not opposed at all. Indeed I didn't know these functions... sounds
a good option. Thanks.

Regards,
Marcos Douglas