[Lcd4linux-devel] lcd4linux: timers and timer groups

[Michael R. <mi...@re...>]

Hello everybode,

to sum up some of the previous mails:

1. I don't like the idea of linked lists for timers (I like linked lists, but not in every case. In german we say "If 
you have a hammer, everything looks like a nail" :-)

The current "variable length array" approach results in a single memory object, which grows at the beginning, but should 
stay at constant size and memroy location. Timers come and go, but the maximum number of timers should be constant.

A (double) linked list has several memory objects. As many timers are "one-shot timers" they may be created and 
destroyed very regularly. This would lead to lots of malloc()/free() calls.


2. Probably I have found the problem with "twice evaluation": there are some lines of code in timer.c (but probably not 
in timer_group.c):

     /* one-shot timers should NOT fire immediately, so delay them by a
        single timer interval */
     if (one_shot) {
	timer_inc(timer, &now);
     }

so even if a new timer is added to the list after the currently being processed timer, it will not be triggered in the 
current loop.


3. I think having both timers and timer groups is a nuisance. Why do we have this? probably because timer-groups has 
been added as a "enhancement" which should not change current behaviour?

Shall we try to "merge" them?

IIRC the timer-groups have been introduced to avoid "fading" of timers because of different execution time... is this 
correct? is there any other reason for having these groups?

I think there should be a better solution for this. probably some kind of "quantisation", which means that timers cannot 
have an arbitrary execution time, but must fit into defined values (eg every 10 msec). So if a 50 msec timer which is 
executed at 352 msec would get executed next time not at 402 msec, but rounded down to 350 msec


Note that I wrote this email without having a close look at the code, so I may be plain wrong :-)




regards, Michael



-- 
Michael Reinelt <mi...@re...>
http://home.pages.at/reinelt
GPG-Key 0xDF13BA50
ICQ #288386781