netcamlbox: checking the mail box without waiting

Hello,

I am trying to use netcaml3 mailbox to
allow a coordinator process to distribute
tasks among worker processes. To do this
I must check if any process's message box has
space. If so I place a request for task
execution otherwise I go on and do something
else (process worker responses).

To check the mail box free space I tried to use:
   let n = Netcamlbox.camlbox_messages wname in

and if (n - message_size) I proceed with the
blocking calls (wait and send). My problem
is that when I call this function from the
coordinator process I get:

Fatal error: exception Unix.Unix_error(20, "shm_open", "/camlbox_9838_0")
Raised by primitive operation at unknown location
Called from file "netcamlbox.ml", line 322, characters 4-21

For testing purposes I used:

   let wslots = 2 in (* maximum of two messages queued for each worker *)
   let wboxes =  Array.init n_workers
                   ( fun k ->
                     let wname = mname ^ "_" ^ string_of_int k in
                     let wbox, _, ws = prep_mbox wname wslots msg_size in
                     let n = Netcamlbox.camlbox_messages wname in
                     (wname, wbox, ws) ) in
   let coord_box = (mname, mbox, mfd, ms) in
   let worker_boxs = wboxes in
   coord_box, worker_boxs

My question is: how do I go about avoiding the block
on a mailing box?

TIA,
Hugo F.





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