model "lift-passengers" and concurrent programming

Hi,

I'm trying to write a model of an elevator with one button. Elevator can
take passengers along the way when going down.

But in my code some error. Because passengers press a button only when
the elevator carries passengers. And no passengers push the button when
the elevator is free.

I took a producer-consumer model.


require 'semaphore'
t0 = Time.now

max=5#the maximum number of passengers
c = 10#number of iterations

tp = []#producer
tc = []#consumer


ffrom=Array.new(max)#floor, where the button is pressed
fto=Array.new(max)#floor, which requires the passenger

prod_from=[]#producer: floor where the passenger has been taken
prod_to=[]#producer:floor where the passenger has arrived
cons_from=[]#consumer: floor where the passenger has been taken
cons_to=[]#floor where the passenger has arrived

buf = Array.new(max)#buffer of lift
s1 = Semaphore.new(buf.size)#overflow protection
s2 = Semaphore.new(0)
m  = Semaphore.new(1)
first=true

producer = Thread.new do#producer
  i = 0
  j=0
  c.times do
    #sleep(rand(5)%5)
    good_pas=false
    m.P
    d = rand(8)+1
    puts "button is pressed on the #{d}th floor" unless(first)
    unless(first)then
      if((d>fto[j])and(d<=ffrom[j]))then
        good_pas=true
        puts "passenger can be allowed\n"
      else
        puts "passenger can't be allowed\n"
      end
    end
    j = ( j + 1 ) % buf.size unless(first)
    m.V unless(good_pas)
    ffrom[i]=d
    fto[i]=rand(8)+1;
    first=false
    while(fto[i]==ffrom[i])do fto[i]=rand(8)+1;  end
    prod_from<<ffrom[i]
    prod_to<<fto[i]
    tp << d
    s1.P
    m.P unless(good_pas)
    puts "\nfrom the #{ffrom[i]}th floor passenger came and asked for
#{fto[i]}th floor"
    buf[i] = d
    m.V
    s2.V
    i = ( i + 1 ) % buf.size
  end
end

consumer = Thread.new do#consumer
  i = 0
  c.times do
    s2.P
    m.P
    d = buf[i]
    puts "\npassenger arrived from the #{ffrom[i]}th floor to the
#{fto[i]}th floor"
    cons_from<<ffrom[i]
    cons_to<<fto[i]
    m.V
    s1.V
    tc << d
    i = ( i + 1 ) % buf.size
  end
end

producer.join
consumer.join

puts "\nproducer - floors where the passenger went into the
lift:\n\t["+prod_from.join(',')+"]"
puts "produser - floor where the passenger came out of the
lift:\n\t["+prod_to.join(',')+"]"
puts "consumer - floor where the passenger went into the
lift:\n\t["+cons_from.join(',')+"]"
puts "consumer - floor where the passenger came out of the
lift:\n\t["+cons_to.join(',')+"]"

puts "\n\n:prod_from==cons_from: #{prod_from==cons_from}"
puts "\nprod_to==cons_to: #{prod_to==cons_to}"
puts "time: #{Time.now - t0}"


Can someone give me some advice about rhis problem?

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