resource bounded_buffer
   op deposit(item : real)
   op fetch() returns item : real
body bounded_buffer(size : int)
   var buf[0:size-1] : real
   var count : int := 0
   var take_out : int := 0
   var put_in : int := 0
   sem elements := 0
   sem spaces := size
   sem mutex := 1

   write("bounded buffer resource with", size, "slots is alive")

   proc deposit(item)
      P(spaces)
      buf[put_in] := item
      put_in := (put_in + 1) % size
      P(mutex)
      count++
      write("deposit: there are now", count, "items in the buffer")
      V(mutex)
      V(elements)
   end deposit

   proc fetch() returns item
      P(elements)
      item := buf[take_out]
      take_out := (take_out + 1) % size
      P(mutex)
      count--
      write("fetch: there are now", count, "items in the buffer")
      V(mutex)
      V(spaces)
   end fetch
end bounded_buffer

resource user()
   import bounded_buffer
   var bb : cap bounded_buffer
   var slots : int := 20, pnap : int := 3, cnap : int := 3
   var run_time : int := 60

   getarg(1, slots); getarg(2, pnap); getarg(3, cnap); getarg(4, run_time)
   writes("main user resource alive, slots = ", slots, ", pnap = ", pnap,
      ", cnap = ", cnap, ", and run_time = ", run_time, "\n")
   bb := create bounded_buffer(slots)

   process producer
      var it : real
      var napping : int
      do true ->
         it := random()
         writes("age=", age(), ", PRODUCER produced item ", it, "\n")
         bb.deposit(it)
         napping := int(random(1000*pnap))
         writes("age=", age(), ", PRODUCER deposited item ", it,
            " and napping for ", napping, "ms\n")
         nap(napping)
      od
   end producer

   process consumer
      var it : real
      var napping : int
      do true ->
         writes("age=", age(), ", consumer wants to consume ...\n")
         it := bb.fetch()
         napping := int(random(1000*cnap))
         writes("age=", age(), ", consumer fetched item ", it,
            " and napping for ", napping, "ms\n")
         nap(napping)
      od
   end consumer

   nap(1000*run_time); write("must stop now"); stop
end user

/* ............... Example compile and run(s)

% sr -o bb bb.sr
% ./bb 5 1 3 10
main user resource alive, slots = 5, pnap = 1, cnap = 3, and run_time = 10
bounded buffer resource with 5 slots is alive
age=50, consumer wants to consume ...
age=53, PRODUCER produced item 0.356596
deposit: there are now 1 items in the buffer
age=66, PRODUCER deposited item 0.356596 and napping for 364ms
fetch: there are now 0 items in the buffer
age=73, consumer fetched item 0.356596 and napping for 316ms
age=418, consumer wants to consume ...
age=449, PRODUCER produced item 0.00800780
deposit: there are now 1 items in the buffer
age=456, PRODUCER deposited item 0.00800780 and napping for 654ms
fetch: there are now 0 items in the buffer
age=464, consumer fetched item 0.00800780 and napping for 2152ms
age=1118, PRODUCER produced item 0.755083
deposit: there are now 1 items in the buffer
age=1131, PRODUCER deposited item 0.755083 and napping for 19ms
age=1158, PRODUCER produced item 0.339312
deposit: there are now 2 items in the buffer
age=1165, PRODUCER deposited item 0.339312 and napping for 138ms
age=1308, PRODUCER produced item 0.212412
deposit: there are now 3 items in the buffer
age=1316, PRODUCER deposited item 0.212412 and napping for 567ms
age=1888, PRODUCER produced item 0.00888645
deposit: there are now 4 items in the buffer
age=1894, PRODUCER deposited item 0.00888645 and napping for 324ms
age=2229, PRODUCER produced item 0.204411
deposit: there are now 5 items in the buffer
age=2253, PRODUCER deposited item 0.204411 and napping for 501ms
age=2629, consumer wants to consume ...
fetch: there are now 4 items in the buffer
age=2636, consumer fetched item 0.755083 and napping for 2215ms
age=2759, PRODUCER produced item 0.727478
deposit: there are now 5 items in the buffer
age=2818, PRODUCER deposited item 0.727478 and napping for 707ms
age=3539, PRODUCER produced item 0.569443
age=4860, consumer wants to consume ...
fetch: there are now 4 items in the buffer
age=4864, consumer fetched item 0.339312 and napping for 1523ms
deposit: there are now 5 items in the buffer
age=4868, PRODUCER deposited item 0.569443 and napping for 732ms
age=5608, PRODUCER produced item 0.989578
age=6398, consumer wants to consume ...
fetch: there are now 4 items in the buffer
age=6407, consumer fetched item 0.212412 and napping for 2838ms
deposit: there are now 5 items in the buffer
age=6411, PRODUCER deposited item 0.989578 and napping for 462ms
age=6879, PRODUCER produced item 0.996745
age=9362, consumer wants to consume ...
fetch: there are now 4 items in the buffer
age=9371, consumer fetched item 0.00888645 and napping for 1097ms
deposit: there are now 5 items in the buffer
age=9375, PRODUCER deposited item 0.996745 and napping for 68ms
age=9448, PRODUCER produced item 0.0306415
must stop now
% ./bb 5 3 1 10
main user resource alive, slots = 5, pnap = 3, cnap = 1, and run_time = 10
bounded buffer resource with 5 slots is alive
age=73, consumer wants to consume ...
age=77, PRODUCER produced item 0.382618
deposit: there are now 1 items in the buffer
age=88, PRODUCER deposited item 0.382618 and napping for 1857ms
fetch: there are now 0 items in the buffer
age=96, consumer fetched item 0.382618 and napping for 867ms
age=980, consumer wants to consume ...
age=1950, PRODUCER produced item 0.0659844
deposit: there are now 1 items in the buffer
age=1956, PRODUCER deposited item 0.0659844 and napping for 133ms
fetch: there are now 0 items in the buffer
age=1960, consumer fetched item 0.0659844 and napping for 669ms
age=2100, PRODUCER produced item 0.714716
deposit: there are now 1 items in the buffer
age=2111, PRODUCER deposited item 0.714716 and napping for 2716ms
age=2640, consumer wants to consume ...
fetch: there are now 0 items in the buffer
age=2647, consumer fetched item 0.714716 and napping for 517ms
age=3180, consumer wants to consume ...
age=4840, PRODUCER produced item 0.653636
deposit: there are now 1 items in the buffer
age=4846, PRODUCER deposited item 0.653636 and napping for 2656ms
fetch: there are now 0 items in the buffer
age=4849, consumer fetched item 0.653636 and napping for 927ms
age=5780, consumer wants to consume ...
age=7510, PRODUCER produced item 0.992305
deposit: there are now 1 items in the buffer
age=7516, PRODUCER deposited item 0.992305 and napping for 2629ms
fetch: there are now 0 items in the buffer
age=7520, consumer fetched item 0.992305 and napping for 76ms
age=7600, consumer wants to consume ...
must stop now
                                              */