Media Share 9/MEDIASHARE_09.ISO/progmisc/euphor10.zip/SCHED.E

Text File | 1993-01-12 | 2KB | 88 lines

-- 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