semaphore unlock after timeout

[apkotelnikov]

This is not safe because it leads to race conditions which semaphores prevent. Can you explain why do you need this? If your function can fail due to an error you should execute it using pcall().

Ok thanks, 

what i am trying to achieve is to have a event script, switch on a group, start a timer then, timeout and switch off a group (also block the resident script from running again while the timer is running ) 
the event script is triggered by an security alarm message which can happen quite fast (every time the pir is triggered, this is why i want to block the script from running if it has been triggered so i don't have multiple scripts running)

are you able to point me in the right direction. 

Many Thanks

Hi!
Perhaps my solution will be useful.
You must create a resident script

Code:

local my_tmr_table = storage.get('my_timers')
if my_tmr_table then
    for my_grp,tmr in pairs(my_tmr_table) do
       local my_grp_name = grp.alias(my_grp)
       if my_grp_name then
         if (os.time() - tmr[1]) > tmr[2] then
            grp.write(my_grp,0)
            my_tmr_table [my_grp_name] = nil
         end
        else
         my_grp = nil
        end
    end
end
storage.set('my_timers', my_tmr_table)

This resident script runs every second and load group objects with UNIX time when timer set (tmr[1]) and for which duration timer set (tmr[2]). If timer for specific group is run out, timer will be destroyed.
Also you need function to set timer

Code:

function my_timer (my_grp , on_t , dur)
   local my_tmr_table = storage.get('my_timers')
   if my_tmr_table then
   else
      my_tmr_table = {}
   end
   k = grp.alias(my_grp)
   my_tmr_table[k] = {on_t,dur}
   storage.set('my_timers',my_tmr_table)
end

Arguments is:
my_grp - group name
on_t      - UNIX time at timer setup
dur        - duration in seconds
Now you can make script for an group address like this

Code:

if event.getvalue()  then
   my_timer (event.dst , os.time() , 300)
end

In the example above, timer is set to 300 seconds.

Anton