[Caml-list] Client/Server socket communication

[IKEDA Katsumi <ikeda@msi.co.jp>]

Hi,

I use Ocaml 3.06 on Vine Linux 2.1.5.
Vine Linux is RedHat 5.* and 6.* based distribution and ...
  kernel: 2.2.18
  libc:   6 -> 2.1.3

I make Client/Server socket communication program.

The followings are the lists.

---------------- server.ml ----------------
(* server.ml *)

let openSock port = 
  let sock = Unix.socket Unix.PF_INET Unix.SOCK_STREAM 0 in
  begin
    Unix.bind sock (Unix.ADDR_INET(Unix.inet_addr_any,port));
    Unix.listen sock 20;
    sock
  end
;;

let waitChild s = 
  print_string "server: waitChild called\n";
  flush stdout ;
  let s =  Unix.waitpid [ Unix.WNOHANG ] 0 in ()
;;

let main() =
  Sys.set_signal Sys.sigchld (Sys.Signal_handle waitChild) ;
  print_string "server started.\n";
  flush stdout;
  let port = 999999 in
  let sock = openSock port in
  begin
    while true do
      try
        let (fd,a) = Unix.accept sock in 
        begin
          print_string "server accepted \n"; 
          flush stdout;
          let pid = Unix.fork() in
          match pid with
            0  ->
	      begin
		print_string "run a child process.\n";
		flush stdout;
		let buf = String.create 10 in
		let ret = Unix.read fd buf 0 10 in
		begin
		  print_string "ret = "; print_int ret; print_newline();
		  print_string buf; print_newline();
		  flush stdout;
		  Unix.sleep(3);
		  print_string "exit a child process.\n";
		  flush stdout;
		  exit 0
		end
              end
	  | _ -> (* parent process *)
              begin
		print_string "server parent side\n";
		flush stdout ;
              end
	end
      with
	Unix.Unix_error(err, ctx1, ctx2) ->
	  if (err = Unix.EINTR) then
	    print_string "Function interrupted by signal\n"
 	  else
	    begin
	      print_string "Unix.Unix_error in main\n";
	    end
      | _ -> print_string "Unexpected Exception\n"
    done;
  end
;;

main();;
--------------------------------

---------------- client.ml ----------------
let main() =
  let server_address =  "127.0.0.1" and port = 999999 in
  let sock = Unix.socket Unix.PF_INET Unix.SOCK_STREAM 0 in
  Unix.connect sock(Unix.ADDR_INET((Unix.inet_addr_of_string server_address),
				   port));
  let msg = "Hello!" in
  let ret = Unix.write sock msg 0 (String.length msg) in
  print_string "reg = "; print_int ret; print_newline();
  flush stdout;
  Unix.close sock;
;;

main();;
----------------

I compiled these by ocamlc.

Now, I make run_client.sh script

---------------- run_client.sh ----------------
#!/bin/sh
./client &
./client &
./client &
./client &
./client &
./client &
./client &
./client &
./client &
./client &
--------------------------------

I run "./server &".
Then I run "./run_client.sh" several times.

I found something wrong.
I run "ps" command, it displays the following:

  PID TTY          TIME CMD
 1225 pts/3    00:00:00 sh
 3156 pts/3    00:00:00 server
 3197 pts/3    00:00:00 server <defunct>
 3226 pts/3    00:00:00 ps

Why "server <defunct>" is occurred.
What do I have to do to correct <defunct> ?

thanks.

-- 
IKEDA Katsumi  <ikeda@msi.co.jp>
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