The QNX Operating System

Listing 2 (holder.c)

/**********************************************************
***
***    Program to illustrate message passing under QNX.
***    Written and tested under QNX version 2.15C atp
***    Compiler used: Quantum's C compiler
***
***    holder.c is meant to be run in the background and
***    provides the following services to the sender.c
***    (<a href="/showArticle.jhtml?documentID=cuj9109busigin&pgno=4">listing 3</A>) program:
***
***    1)  Store a text string.
***    2)  Reply with a previously stored string.
***    3)  Commit suicide.
***
***    The action carried out depends on the value of the
***    header word of the message that sender.c sends to
***    holder.c.
***
***********************************************************/

#include <stdio.h>
#include <task_msgs.h>
#include "message.h"

#define INIT_MSG       "*** No stored messages ***"

main(argc, argv)
int argc;
char **argv;
{
   unsigned stid;              /* Variable to hold
                             sender's task id.     */
   unsigned rtid;              /* Variable to hold
                             this task's task id.  */
   struct message buff, rbuff; /* Message buffers       */
   extern char Cmd_flags;      /* Magic variable        */

/*
   If any arguments have been passed to this program or if
   the program has not been run in background mode, print
   a command usage message and exit.
*/
   if (argc!= 1 || (Cmd_flags & RUN_BACKGROUND) == 0 )
   {
      printf("\nUsage:  holder &\n");
      exit(-1);
   }
/*
   Register a name with the operating system so that other
   tasks can find out its task id.
*/
   if((rtid = name_attach(HOLDER_NAME, 0)) == 0)
   {
      printf("\nholder task couldn't attach name\n");
      exit(-1);
   }
/*
   Initialize the reply buffer with an initial text
   string.
*/
   strcpy(rbuff.text, INIT_MSG);

/*
   Now wait for a message. Upon receiving a message,
   carry out the appropriate action based on the header
   word of the message. Then reply with the result to
   the sending task.
*/
   for (;;)
   {
      stid = receive(0, &buff, sizeof(buff) );
      switch (buff.mssg_type)
      {
         case STORE:
            strcpy(rbuff.text, buff.text);
            rbuff.mssg_type = STORED;
            break;
         case RETRIEVE:
            rbuff.mssg_type = RETRIEVED;
            break;
         case KILL: /* de-register name & die. */
            name_detach(HOLDER_NAME, rtid);
            exit(0);
            break;
         default:
            rbuff.mssg_type = ERROR;
            break;
      }
      reply(stid, &rbuff, sizeof(rbuff) );
   }

}

/* End of File */