resource server
   op Start_Read(i : int), End_Read(i : int)
   op Start_Write(i : int), End_Write(i : int)
body server()
   write("readers and writers server is alive")
   var Readers : int := 0
   sem mutex := 1
   sem OK := 1

   proc Start_Read(i)
      P(mutex)
      Readers++
      if Readers = 1 ->
         write("age=", age(), "reader", i, "waiting to read, Readers=",
            Readers)
         P(OK)
      fi
      write("   age=", age(), "reader", i, "has begun reading, Readers=",
         Readers)
      V(mutex)
   end Start_Read

   proc End_Read(i)
      P(mutex)
      Readers--
      write("   age=", age(), "reader", i, "finished reading, Readers=",
         Readers)
      if Readers = 0 -> V(OK) fi
      V(mutex)
   end End_Read

   proc Start_Write(i)
      P(OK)
      write("      age=", age(), "WRITER", i, "has begun Writing,")
   end Start_Write

   proc End_Write(i)
      write("   age=", age(), "WRITER", i, "has finished Writing")
      V(OK)
   end End_Write
end server

resource reader
   import server
body reader(i : int; scap : cap server; nap_time : int)
   write("reader", i, "is alive, nap_time =", nap_time)

   process reading
      var napping : int
      do true ->
         napping := int(random(1000*nap_time))
         write("age=", age(), "reader", i, "napping for", napping)
         nap(napping)
         write("age=", age(), "reader", i, "wants to read")
         scap.Start_Read(i)
         napping := int(random(1000*nap_time))
         write("age=", age(), "reader", i, "begins reading for", napping)
         nap(napping)
         scap.End_Read(i)
         write("age=", age(), "reader", i, "finished reading")
      od
   end reading
end reader

resource writer
   import server
body writer(i : int; scap : cap server; nap_time : int)
   write("WRITER", i, "is alive, nap_time =", nap_time)

   process writing
      var napping : int
      do true ->
         napping := int(random(1000*nap_time))
         write("age=", age(), "WRITER", i, "napping for", napping)
         nap(napping)
         write("age=", age(), "WRITER", i, "wants to write")
         scap.Start_Write(i)
         napping := int(random(1000*nap_time))
         write("age=", age(), "WRITER", i, "is writing for", napping)
         nap(napping)
         write("age=", age(), "WRITER", i, "is finished writing")
         scap.End_Write(i)
      od
   end writing
end writer

resource start()
   import writer, reader, server
   var readers : int := 10, writers : int := 5, nap_time : int := 3
   var run_time : int := 60
   var scap : cap server
   getarg(1, readers); getarg(2, writers); getarg(3, nap_time)
   getarg(4, run_time)
   write(readers, "readers and", writers,
      "writers starting with nap_time", nap_time, "and run_time", run_time)
   scap := create server()
   fa i := 1 to readers -> create reader(i, scap, nap_time) af
   fa i := 1 to writers -> create writer(i, scap, nap_time) af
   nap(1000*run_time); write("must stop now"); stop
end start

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

% sr -o rdwr rdwr.sr
% ./rdwr 3 2 1 10
3 readers and 2 writers starting with nap_time 1 and run_time 10
readers and writers server is alive
reader 1 is alive, nap_time = 1
age= 223 reader 1 napping for 506
reader 2 is alive, nap_time = 1
age= 233 reader 2 napping for 694
reader 3 is alive, nap_time = 1
age= 509 reader 3 napping for 27
WRITER 1 is alive, nap_time = 1
age= 641 WRITER 1 napping for 338
age= 658 reader 3 wants to read
age= 670 reader 3 waiting to read, Readers= 1
   age= 727 reader 3 has begun reading, Readers= 1
age= 732 reader 3 begins reading for 60
WRITER 2 is alive, nap_time = 1
age= 738 WRITER 2 napping for 565
age= 743 reader 1 wants to read
   age= 746 reader 1 has begun reading, Readers= 2
age= 749 reader 1 begins reading for 500
   age= 804 reader 3 finished reading, Readers= 1
age= 815 reader 3 finished reading
age= 822 reader 3 napping for 712
age= 934 reader 2 wants to read
   age= 937 reader 2 has begun reading, Readers= 2
age= 942 reader 2 begins reading for 166
age= 995 WRITER 1 wants to write
   age= 1114 reader 2 finished reading, Readers= 1
age= 1117 reader 2 finished reading
age= 1123 reader 2 napping for 514
   age= 1255 reader 1 finished reading, Readers= 0
age= 1260 reader 1 finished reading
age= 1263 reader 1 napping for 545
      age= 1266 WRITER 1 has begun Writing,
age= 1269 WRITER 1 is writing for 796
age= 1314 WRITER 2 wants to write
age= 1553 reader 3 wants to read
age= 1559 reader 3 waiting to read, Readers= 1
age= 1701 reader 2 wants to read
age= 1825 reader 1 wants to read
age= 2075 WRITER 1 is finished writing
   age= 2146 WRITER 1 has finished Writing
age= 2174 WRITER 1 napping for 555
      age= 2193 WRITER 2 has begun Writing,
age= 2207 WRITER 2 is writing for 964
age= 2754 WRITER 1 wants to write
age= 3212 WRITER 2 is finished writing
   age= 3218 WRITER 2 has finished Writing
age= 3219 WRITER 2 napping for 821
   age= 3221 reader 3 has begun reading, Readers= 1
age= 3222 reader 3 begins reading for 471
   age= 3223 reader 2 has begun reading, Readers= 2
age= 3225 reader 2 begins reading for 286
   age= 3226 reader 1 has begun reading, Readers= 3
age= 3227 reader 1 begins reading for 808
   age= 3515 reader 2 finished reading, Readers= 2
age= 3685 reader 2 finished reading
age= 3733 reader 2 napping for 739
   age= 3784 reader 3 finished reading, Readers= 1
age= 3822 reader 3 finished reading
age= 3883 reader 3 napping for 294
   age= 4044 reader 1 finished reading, Readers= 0
age= 4050 reader 1 finished reading
age= 4053 reader 1 napping for 615
age= 4056 WRITER 2 wants to write
      age= 4059 WRITER 1 has begun Writing,
age= 4062 WRITER 1 is writing for 689
age= 4285 reader 3 wants to read
age= 4289 reader 3 waiting to read, Readers= 1
age= 4523 reader 2 wants to read
age= 4673 reader 1 wants to read
age= 4763 WRITER 1 is finished writing
   age= 4766 WRITER 1 has finished Writing
age= 4768 WRITER 1 napping for 100
      age= 4769 WRITER 2 has begun Writing,
age= 4770 WRITER 2 is writing for 505
age= 4873 WRITER 1 wants to write
age= 5334 WRITER 2 is finished writing
   age= 5339 WRITER 2 has finished Writing
age= 5340 WRITER 2 napping for 704
   age= 5341 reader 3 has begun reading, Readers= 1
age= 5343 reader 3 begins reading for 575
   age= 5344 reader 2 has begun reading, Readers= 2
age= 5346 reader 2 begins reading for 673
   age= 5347 reader 1 has begun reading, Readers= 3
age= 5348 reader 1 begins reading for 941
   age= 5923 reader 3 finished reading, Readers= 2
age= 5928 reader 3 finished reading
age= 5929 reader 3 napping for 844
   age= 6023 reader 2 finished reading, Readers= 1
age= 6026 reader 2 finished reading
age= 6028 reader 2 napping for 631
age= 6053 WRITER 2 wants to write
   age= 6294 reader 1 finished reading, Readers= 0
age= 6298 reader 1 finished reading
age= 6299 reader 1 napping for 543
      age= 6300 WRITER 1 has begun Writing,
age= 6301 WRITER 1 is writing for 650
age= 6664 reader 2 wants to read
age= 6678 reader 2 waiting to read, Readers= 1
age= 6783 reader 3 wants to read
age= 6935 reader 1 wants to read
age= 6953 WRITER 1 is finished writing
   age= 6956 WRITER 1 has finished Writing
age= 6958 WRITER 1 napping for 837
      age= 6959 WRITER 2 has begun Writing,
age= 6962 WRITER 2 is writing for 12
age= 6986 WRITER 2 is finished writing
   age= 7000 WRITER 2 has finished Writing
age= 7001 WRITER 2 napping for 93
   age= 7002 reader 2 has begun reading, Readers= 1
age= 7004 reader 2 begins reading for 337
   age= 7005 reader 3 has begun reading, Readers= 2
age= 7007 reader 3 begins reading for 448
   age= 7008 reader 1 has begun reading, Readers= 3
age= 7009 reader 1 begins reading for 782
age= 7104 WRITER 2 wants to write
   age= 7344 reader 2 finished reading, Readers= 2
age= 7358 reader 2 finished reading
age= 7360 reader 2 napping for 345
   age= 7466 reader 3 finished reading, Readers= 1
age= 7470 reader 3 finished reading
age= 7471 reader 3 napping for 662
age= 7733 reader 2 wants to read
   age= 7751 reader 2 has begun reading, Readers= 2
age= 7753 reader 2 begins reading for 391
   age= 7793 reader 1 finished reading, Readers= 1
age= 7797 reader 1 finished reading
age= 7798 reader 1 napping for 660
age= 7799 WRITER 1 wants to write
age= 8143 reader 3 wants to read
   age= 8146 reader 3 has begun reading, Readers= 2
age= 8148 reader 3 begins reading for 478
   age= 8150 reader 2 finished reading, Readers= 1
age= 8151 reader 2 finished reading
age= 8152 reader 2 napping for 790
age= 8467 reader 1 wants to read
   age= 8470 reader 1 has begun reading, Readers= 2
age= 8472 reader 1 begins reading for 687
   age= 8633 reader 3 finished reading, Readers= 1
age= 8636 reader 3 finished reading
age= 8637 reader 3 napping for 812
age= 8943 reader 2 wants to read
   age= 8946 reader 2 has begun reading, Readers= 2
age= 8948 reader 2 begins reading for 458
   age= 9163 reader 1 finished reading, Readers= 1
age= 9166 reader 1 finished reading
age= 9167 reader 1 napping for 399
   age= 9413 reader 2 finished reading, Readers= 0
age= 9416 reader 2 finished reading
age= 9417 reader 2 napping for 884
      age= 9419 WRITER 2 has begun Writing,
age= 9420 WRITER 2 is writing for 737
age= 9453 reader 3 wants to read
age= 9456 reader 3 waiting to read, Readers= 1
age= 9573 reader 1 wants to read
age= 10163 WRITER 2 is finished writing
   age= 10166 WRITER 2 has finished Writing
age= 10168 WRITER 2 napping for 43
      age= 10169 WRITER 1 has begun Writing,
age= 10170 WRITER 1 is writing for 799
age= 10213 WRITER 2 wants to write
age= 10303 reader 2 wants to read
must stop now
                                              */