#
# The Dining Philosophers - thread example
#
require "xlib"
require "thread"

include Xlib
include Math

$dis = Display.new
$white = $dis.alloc_color 'white'
$win = $dis.root.new_window 320,320,nil,true
$win.pixel = $white
$gc = $win.new_gc
$win.title = 'The Dining Philosophers - thread example'
$win.show
$color = {
  'none'  => 'blue' ,
  'eat'   => 'red'  ,
}
$color.each { |key, value|
  $color[key] = $dis.alloc_color value
}

PHILOS_SIZE = 32

class << $gc
  def draw_philos(n, act)
    angle = 2*PI*n/N
    x = cos(angle) * $win.width  * 0.4 + $win.width  / 2
    y = sin(angle) * $win.height * 0.4 + $win.height / 2
    r = PHILOS_SIZE
    area = Rect.new((x-r/2).to_i, (y-r/2).to_i, r, r)
    $gc.fg = $color[act]
    $gc.fill_oval area, 0, 360*64
  end
end

srand
N=9				# number of philosophers
$forks = []
$eat_p = []
for i in 0..N-1
  $forks[i] = Mutex.new
  $eat_p[i] = false
end

def redraw
  for i in 0..N-1
    $gc.draw_philos i, if $eat_p[i] then 'eat' else 'none' end
  end
end

redraw
$dis.flush

def wait
  sleep rand(20)/10.0
end

def think(n)
  wait
end

def eat(n)
  $gc.draw_philos n, 'eat'
  $eat_p[n] = true
  wait
  $eat_p[n] = false
  $gc.draw_philos n, 'none'
end

def philosopher(n)
  while TRUE
    think n
    $forks[n].lock
    if not $forks[(n+1)%N].try_lock
      $forks[n].unlock		# avoid deadlock
      next
    end
    eat n
    $forks[n].unlock
    $forks[(n+1)%N].unlock
  end
end

$win.event 'exposed' do redraw; end

for i in 0..N-1
  Thread.start{philosopher(i)}
  sleep 0.1
end

while $dis.event; $dis.sync; end