Category : Miscellaneous Language Source Code
Archive   : EUPHOR10.ZIP
Filename : SCHED.E

-- sched.e
-- Task Scheduler

global constant HUGE_TIME = 1e30

constant sample_interval = 1.0
atom sample_count

type reasonable_delay(atom x)
return x > 0 and x < 30
end type

global procedure init_delay()
-- since time() may not have fine enough
-- resolution for small delays, we see how many for-loop iterations
-- we can complete over a small sample period

atom t

t = time() + sample_interval
for i = 1 to 999999999 do
if time() < t then
else
sample_count = i
exit
end if
end for
end procedure

global procedure delay(reasonable_delay t)
-- delay for t seconds
atom stop
if t > sample_interval then
-- time() should be precise enough
stop = time() + t
while time() < stop do
end while
else
-- loop a certain number of times
stop = time() + sample_interval
for i = 1 to floor(t / sample_interval * sample_count) do
if time() < stop then
else
end if
end for
end if
end procedure


global procedure sched(task t, positive_atom wait)
-- schedule task to be reactivated in wait seconds

if wait = 0 then
-- deactivate
tcb[t] = HUGE_TIME
else
-- activate in wait seconds from now
tcb[t] = time() + wait
end if
end procedure


global function next_task()
-- choose the next task to be executed

positive_atom mintime
task mintask

-- find task with minimum time
mintime = HUGE_TIME
for i = 1 to NTASKS do
if tcb[i] < mintime then
mintask = i
mintime = tcb[i]
end if
end for

-- subtract it's early-activation tolerance
tcb[mintask] = tcb[mintask] - eat[mintask]

-- wait until it is time to activate it
while time() < tcb[mintask] do
end while

return mintask
end function