[OS:N:] Multithreaded RPC Servers for Linux.Thread-safe code writing

["Boris Derzhavets" <derzhavets hotmail com>]

This article is supposed to give a positive answer for the question 23.10 
from [1] Chapter "RPC".
Actually code published in [1] utilizes static variables what causes 
question 23.10 from [1]
(about multhreaded implementation of RPC Server under Linux) to produce some 
confusion.
Originally only two files are taken from [1]: rdict.x  and rdict_srp.c. All 
business logic is implemented into rdict_client.c - file generated by 
command:
    $ rpcgen -a -M rdict.x
Files rdict.c and rdict_cif.c (see [1] , Chapter "RPC") are taken out to 
highlight the core of RPC technology either "Sun" or "DCE"
Remember -A option of rpcgen is not supported under Linux.Library calls 
providing by SunOS RPC to build Multithreaded RPC Server are unavailable 
under Linux as well.
I've never got a chance to take a look at "Sun RPC" or "DCE RPC" libraries 
code
My guess would be that code developed bellow could be very helpfull for 
Linux developers at this time.
It gives just an example how to manage under Linux.



Source of rdict.x:



const MAXWORD=50;
const DICTSIZ=100;
struct example{
	int exfield1;
	char exfield2;
};
program RDICTPROG {
	version RDICTVERS {
	int INITW(void)=1;
	int INSERTW(string)=2;
	int DELETEW(string)=3;
	int LOOKUPW(string)=4;
	} =1;
} =0x30090949;


Source of rdict_srp.c :


#include <  rpc/rpc.h>
#include <  string.h>
#include "rdict.h"
char dict[DICTSIZ][MAXWORD+1];
static char snd[50];
static int lns;
int nwords=0;
int
initw()
{
	nwords=0;
	return 1;
}
int
insertw(char *word)
{
	strcpy(dict[nwords],word);
	nwords++;
	return nwords;
}
int
deletew(char *word)
{
	int i;
	for(i=0;i <  nwords;i++)
	if(strcmp(word,dict[i])==0)
	 {
		nwords--;
		strcpy(dict[i],dict[nwords]);
		return 1;
	 }
	return 0;
}
int
lookupw(char *word)
{
	int i;
       for(i=0;i  <   nwords;i++)
       if(strcmp(word,dict[i])==0)
            return 1;
	return 0;
}
rdictprog_1_freeresult(SVCXPRT *transp,xdrproc_t xdr_result,
caddr_t result)
{
xdr_free(xdr_result,result);
return(1);
}


Call rpcgen to generate stubs ,header file rdict.h and rdict_xdr:


        $rpcgen -a -M rdict.x


Modified files on server's side follows bellow:
File rdict_sif.c contains thread-safe code instead of utilizing static 
variables
for to return results to client.


/*
*    rdict_sif.c (compare with file rdict_sif.c in [1] chapter "RPC")
*/
#include <  rpc/rpc.h>
#define RPC_SVC
#include "rdict.h"

int initw(void),insertw(char *),deletew(char *),lookupw(char *);
bool_t
insertw_1_svc(char **w,int *ptr_retcode,struct svc_req *rqstp)
{
	*ptr_retcode=insertw(*(char **)w);
         return(TRUE);
}
bool_t
initw_1_svc(void *w,int *ptr_retcode,struct svc_req *rqstp)
{
       *ptr_retcode=initw();
         return(TRUE);
}
bool_t
deletew_1_svc(char **w,int *ptr_retcode,struct svc_req *rqstp)
{
       *ptr_retcode=deletew(*(char **)w);
         return(TRUE);
}
bool_t
lookupw_1_svc(char **w,int *ptr_retcode,struct svc_req *rqstp)
{
       *ptr_retcode=lookupw(*(char **)w);
         return(TRUE);
}


Modified server's stub is file rdict_svc.c .
Multithreaded version


/*                       Modified rdict_svc.c
*
* Please do not edit this file.
* It was generated using rpcgen.
*/

#include "rdict.h"
#include  <  stdio.h>
#include  <  stdlib.h>
#include  <  rpc/pmap_clnt.h>
#include  <  string.h>
#include  <  memory.h>
#include  <  sys/socket.h>
#include  <  netinet/in.h>

#ifndef SIG_PF
#define SIG_PF void(*)(int)
#endif
pthread_t p_thread;
pthread_attr_t attr;

/* Procedure to be run by thread */

void *
serv_request(void *data)
{
struct thr_data
{
struct svc_req *rqstp;
SVCXPRT *transp;
} *ptr_data;
	union {
		char *insertw_1_arg;
		char *deletew_1_arg;
		char *lookupw_1_arg;
		char *showupw_1_arg;
		char *getlenw_1_arg;
	} argument;
	union {
		int initw_1_res;
		int insertw_1_res;
		int deletew_1_res;
		int lookupw_1_res;
		char showupw_1_res;
		int getlenw_1_res;
	} result;
	bool_t retval;
	xdrproc_t _xdr_argument, _xdr_result;
	bool_t (*local)(char *, void *, struct svc_req *);

ptr_data = (struct thr_data  *)data;
struct svc_req *rqstp = ptr_data-> rqstp;
register SVCXPRT *transp = ptr_data-> transp;

switch (rqstp-> rq_proc) {
	case NULLPROC:
		(void) svc_sendreply (transp, (xdrproc_t) xdr_void, (char *)NULL);
		return;

	case INITW:
		_xdr_argument = (xdrproc_t) xdr_void;
		_xdr_result = (xdrproc_t) xdr_int;
		local = (bool_t (*) (char *, void *,  struct svc_req *))initw_1_svc;
		break;

	case INSERTW:
		_xdr_argument = (xdrproc_t) xdr_wrapstring;
		_xdr_result = (xdrproc_t) xdr_int;
		local = (bool_t (*) (char *, void *,  struct svc_req *))insertw_1_svc;
		break;

	case DELETEW:
		_xdr_argument = (xdrproc_t) xdr_wrapstring;
		_xdr_result = (xdrproc_t) xdr_int;
		local = (bool_t (*) (char *, void *,  struct svc_req *))deletew_1_svc;
		break;

	case LOOKUPW:
		_xdr_argument = (xdrproc_t) xdr_wrapstring;
		_xdr_result = (xdrproc_t) xdr_int;
		local = (bool_t (*) (char *, void *,  struct svc_req *))lookupw_1_svc;
		break;
	default:
		svcerr_noproc (transp);
		return;
	}
	memset ((char *)&argument, 0, sizeof (argument));
	if (!svc_getargs (transp, (xdrproc_t) _xdr_argument, (caddr_t) &argument)) 
{
		svcerr_decode (transp);
		return;
	}
	retval = (bool_t) (*local)((char *)&argument, (void *)&result, rqstp);
	if (retval >  0 && !svc_sendreply(transp, (xdrproc_t) _xdr_result, (char 
*)&result)) {
		svcerr_systemerr (transp);
	}
	if (!svc_freeargs (transp, (xdrproc_t) _xdr_argument, (caddr_t) &argument)) 
{
		fprintf (stderr, "%s", "unable to free arguments");
		exit (1);
	}
	if (!rdictprog_1_freeresult (transp, _xdr_result, (caddr_t) &result))
		fprintf (stderr, "%s", "unable to free results");

	return;
}

/*
  New code for procedure rdictprog_1 , starting thread
  in response for each clients request to invoke remote
  procedure
*/


static void
rdictprog_1(struct svc_req *rqstp, register SVCXPRT *transp)
{
struct data_str
{
struct svc_req *rqstp;
SVCXPRT *transp;
} *data_ptr=(struct data_str*)malloc(sizeof(struct data_str));
data_ptr-> rqstp = rqstp;
data_ptr-> transp = transp;
pthread_attr_setdetachstate(&attr,PTHREAD_CREATE_DETACHED);
pthread_create(&p_thread,&attr,serv_request,(void *)data_ptr);
}

int
main (int argc, char **argv)
{
	register SVCXPRT *transp;

	pmap_unset (RDICTPROG, RDICTVERS);

	transp = svcudp_create(RPC_ANYSOCK);
	if (transp == NULL) {
		fprintf (stderr, "%s", "cannot create udp service.");
		exit(1);
	}
	if (!svc_register(transp, RDICTPROG, RDICTVERS, rdictprog_1, IPPROTO_UDP)) 
{
		fprintf (stderr, "%s", "unable to register (RDICTPROG, RDICTVERS, udp).");
		exit(1);
	}

	transp = svctcp_create(RPC_ANYSOCK, 0, 0);
	if (transp == NULL) {
		fprintf (stderr, "%s", "cannot create tcp service.");
		exit(1);
	}
	if (!svc_register(transp, RDICTPROG, RDICTVERS, rdictprog_1, IPPROTO_TCP)) 
{
		fprintf (stderr, "%s", "unable to register (RDICTPROG, RDICTVERS, tcp).");
		exit(1);
	}

	svc_run ();
	fprintf (stderr, "%s", "svc_run returned");
	exit (1);
	/* NOTREACHED */
}



 Compile server:


   $ gcc -o  ServerDT rdict_svc.c rdict_sif.c rdict_srp.c rdict_xdr.c 
-lpthread -lnsl


Modified code of rdict_client.c  with implemented business logic.
Template has been already generated by "rpcgen -a -M rdict.x"


/*    File  rdict_client.c  versus  rdict.c&rdict_cif from [1] chapter "RPC"
*
* This is sample code generated by rpcgen.
* These are only templates and you can use them
* as a guideline for developing your own functions.
*/

#include "rdict.h"
#define MAXWORD 50

char buf[80];
void
rdictprog_1(char *host)
{
	CLIENT *clnt;
	enum clnt_stat retval_1;
	int result_1;
	char *initw_1_arg="0";
	enum clnt_stat retval_2;
	int result_2;
	char * insertw_1_arg;
	enum clnt_stat retval_3;
	int result_3;
	char * deletew_1_arg;
	enum clnt_stat retval_4;
	int result_4;
	char * lookupw_1_arg;
int ch;
char cmd;
char word[MAXWORD+1];
int wrdlen;

#ifndef	DEBUG
	clnt = clnt_create (host, RDICTPROG, RDICTVERS, "udp");
	if (clnt == NULL) {
		clnt_pcreateerror (host);
		exit (1);
	}
#endif	/* DEBUG */
while(1)
{
wrdlen=nextin(&cmd,word);
if(wrdlen  <   0)
exit(0);
word[wrdlen]='\0';
switch(buf[0])
{
case 'I':
	retval_1 = initw_1((void*)&initw_1_arg, &result_1, clnt);
	if (retval_1 != RPC_SUCCESS) {
		clnt_perror (clnt, "call failed");
	}
      if (result_1 == 1)
       printf("Dictionary was initialized \n");
      else
       printf("Dictionary failed to initialize \n");
      break;
case 'i':
       insertw_1_arg=word;
	retval_2 = insertw_1(&insertw_1_arg, &result_2, clnt);
	if (retval_2 != RPC_SUCCESS) {
		clnt_perror (clnt, "call failed");
	}
   if (result_2 > 0 )
     printf("Insert was done\n");
   else
     printf("Insert failed\n");
       break;
case 'd':
       deletew_1_arg=word;
	retval_3 = deletew_1(&deletew_1_arg, &result_3, clnt);
	if (retval_3 != RPC_SUCCESS) {
		clnt_perror (clnt, "call failed");
	}
    if (result_3 == 1 )
       printf("Delete was done\n");
    else
      printf("Delete failed\n");
       break;
case 'l':
       lookupw_1_arg=word;
	retval_4 = lookupw_1(&lookupw_1_arg, &result_4, clnt);
	if (retval_4 != RPC_SUCCESS) {
		clnt_perror (clnt, "call failed");
	}
       if (result_4 == 1)
         printf("Word '%s' was found\n",word);
       else
         printf("Word '%s' was not found\n",word);
       break;
case 'q':
       printf("Programm quits \n");
       exit(0);
default:
      printf("Command invalid\n");
      break;
}
}
#ifndef	DEBUG
	clnt_destroy (clnt);
#endif	 /* DEBUG */
}
int
nextin(char *cmd,char *word)
{
       int i,ch;
       printf("\n");
       printf("***** Make a choice ******\n");
       printf("1. I(initialize dictionary)\n");
       printf("2. i(inserting word) \n");
       printf("3. l(looking for word)\n");
       printf("4. d(deleting word)\n");
       printf("5. q(quit)\n");
       printf("***************************\n");
       printf("Command prompt => \t");
       ch=getc(stdin);
       while(isspace(ch))
               ch=getc(stdin);
       if(ch==EOF)
               return -1;
       *cmd=(char)ch;
       sprintf(buf,"%s",cmd);
       if(buf[0] == 'q' || buf[0] == 'I')
                return 0;
        printf("*****************\n");
        printf("Analysing Command\n");
        printf("*****************\n");
        if(buf[0]=='i' || buf[0]=='l'|| buf[0]=='d')
         {
           printf("Input word  => \t");
         }
         else
         {
             return 0;
         }
        ch=getc(stdin);
       while(isspace(ch))
              ch=getc(stdin);
       if(ch==EOF)
               return -1;
       if(ch=='\n')
               return 0;
       i=0;
       while(!isspace(ch))
       {
               if(++i> MAXWORD)
               {
                       printf("Error word to long.\n");
                       exit(1);
               }
               *word++=ch;
               ch=getc(stdin);
       }
       return i;
}
int
main (int argc, char *argv[])
{
	char *host;

	if (argc  <   2) {
		printf ("usage: %s server_host\n", argv[0]);
		exit (1);
	}
	host = argv[1];
	rdictprog_1 (host);
exit (0);
}


Compile client:



    $ gcc -o CientDT rdict_client.c rdict_clnt.c rdict_xdr.c -lnsl


Now we are ready for testing



                        References.

1.Douglas E. Comer,David L. Stevens Internet Working with TCP/IP ,vol 3
  Client-Server Programming and application Linux/Posix Socket Version,
  Prentice Hall,Inc. 2001

_________________________________________________________________
Stop worrying about overloading your inbox - get MSN Hotmail Extra Storage! 
http://join.msn.click-url.com/go/onm00200362ave/direct/01/