[fpc-devel] TTimers and TThreads. Attn Michael Schnell

[Giuliano Colla]

I've faced problems similar to yours in the past, and I've successfully 
used a simple and quite effective scheme:

1) a list of timer events, ordered by expiration time. Each entry holds 
the absolute time, and the action to take (the semaphore to signal, 
where a thread is waiting, in my case). The queue is built as a double 
linked list, for ease of insertion/deletion.

2) whenever a new timer event must be scheduled, it's inserted in the 
appropriate place of the list. if it happens to go to the head of the 
list, the timer must be reprogrammed, otherwise it's left untouched.

3) When the timer expires, the head item is removed from the list, and 
the action is activated. Optionally, if timer for next event is lower 
than a given threshold, also next event can be activated too, and 
removed from the list.
The timer is reprogrammed from the next item in the list (which has 
become the head of the list).
If the list has become empty, the timer is not reactivated.

Pros: you have only one timer to deal with, no overhead for useless 
timer events, minimal overhead on timer events.
Cons: you have some overhead when programming a timer event, because the 
list must be scanned to insert the event in the appropriate place.

Just my 5 c.

Giuliano