_DISTRIBUTED COMPUTING NOW: DEVELOPMENT ENVIRONMENTS_
by Lowell Schneider

[LISTING ONE]
 
typedef struct {
        binding,                 /* the binding property */
        princ_name,              /* the rpi's principal name */
        secpac,                  /* the rpi's security package */
        ns_auth,                 /* the rpi's privileges in the NSI */
        struct {
                 name,           /* property name */
                 argc,           /* number of values */
                 argv[16]        /* array of values */
        } prop[24],              /* property list */
        propc,                   /* number of properties */
} INQUIRE;
auto INQUIRE inq[ 24 ];
auto cexp = "(('student' in TABLES) or ('enroll' in TABLES ))", i = 0;
*inq[ 0 ] = servers(
                 "",             /* subnet - "" means local subnet */
                 "/.:/",         /* context - in this case every host */
                 cexp,           /* constraint expression */
                 000,            /* secpac - in this case none */
                 ""              /* CDS group -- "" means default
                                    which is  /.:/eos */
);
while( inq[ i ]->binding )
        *inq[ ++i ] = servers();
 


[LISTING TWO]
 
/* Implements a C wrapper around an executable we have no source 
for that turns it into a server. */
#include <stdio.h>
#define MAXBUF  65536
char    stdinb[ MAXBUF ];
int     prlen = 10;
char    prompt[] = "\nbroker=> ";
char    buf[ 3 ][] = { "set stock ", "set shares ", "execute\n" };
char    *arg[ 3 ] = { NULL, NULL, NULL };
char    nul[] = "";
main( argc, argv )
int     argc; 
char    *argv[];
{
        char             *c, *d, tmp[ 255 ];
        int              i, pid, j;
        FILE             *fp[ 2 ];
        int              fdin[ 2 ], fdout[ 2 ];
 
        /* create output pipe to server body */
        if ( pipe( fdout ) == -1 ) exit( 1 );
        if (!( fp[ 1 ] = fdopen( fdout[ 1 ], "w" ))) exit( 2 );
        /* create input pipe from server body */
        if ( pipe( fdin ) == -1 ) exit( 3 );
        if (!( fp[ 0 ] = fdopen( fdin[ 0 ], "r" ))) exit ( 4 );
        /* name of server body to exec */
        strcpy( tmp, "/usr/bin/sbroker" );
        argv[0] = tmp;
        /* start the a new process, which runs on its own. */
        if ((pid = fork()) == -1) exit( 5 );
        /* if in the server body */
        if( pid == 0 ) {
                /* dup our output pipe to servers stdin */
                close( 0 ); 
                dup( fdout[ 0 ] ); 
                /* dup our input pipe to servers stdout */
                close( 1 ); 
                dup( fdin[ 1 ] ); 
                /* execute sbroker program. */
                execlp( tmp, tmp, NULL );
                exit( -1 );

        }
        /* swallow the first prompt */
        for( i = 0; i < prlen; i++ )
                getc( fp[ 0 ] );
        /* forever or until we're told to quit */
        while( 1 ) {
                /* wait for sms to call us */
                if ( !fgets( stdinb, MAXBUF, stdin ))
                         break;
                /* if caller wants us to quit */
                if ( !strcmp( stdinb, "quit\n" ) ) {
                         fputs( stdinb, fp[ 1 ] );
                         fflush( fp[ 0 ] );
                         break;
                }
                /* parse arguments:  should be stock, shares */
                arg[ 0 ] = ( char * )strtok( stdinb, "," );
                arg[ 1 ] = ( char * ) strtok( NULL, "," );
                arg[ 2 ] = null;
                /* begin the "trick" code which turns our single input */
                /* line into three outputs to the server after each of */
                /* which we discard the prompt */
                for ( i = 0; i < 3; i++ ) {
                         fprintf( stdout, "%s %s\n", buf[ i ], arg[ i ] );
                         fflush( stdout );
                         d = c;
                         for( j = 0; j < prlen; j++ ) {
                                 *c = getc( fp[ 0 ] );
                                 if ( *c != prompt[ j ] ) {
                                         c++;
                                         break;
                                 }
                                 if ( *c == '\n' ) *c = '\0';
                                 else 
                                         c++;
                         }
                         *c = '\0';
                         if ( !strcmp( d, ( char *) prompt + 1 )) 
                                 continue;
 
                         fgets( stdinb, MAXBUF, fp[ 0 ] );
                }
                /* this server is implemented as a void function */
                fputs( "\n", stdout );
                fflush( stdout );
                
        }
        exit( 0 );
}


[LISTING THREE]
 
function "clientCB"
{
        auto dir = "/users/me/stock", table = "portfolio", shares, row;
        stable current_portfolio_value; 
        static SERVER model;
        static SERVER broker;
 
        /* import the model server */
        model->TYPE = 112000;
        model->CONTEXT = "/.:/hosts/ferrari/ /.:/";
        model->PROPC = 1;
        model->PROPV[ 0 ] = "'finsim' in sblist";
        *model = rpi( *model );
        (model->INITIALIZE)( "model", "finsim", "quit" );
        /* import the broker server */
        broker->TYPE = 112000;
        broker->CONTEXT = "/.:/";
        broker->PROPC = 1;
        broker->PROPV[ 0 ] = "'sbroker' in sblist";
        *broker = rpi( *broker );
        (model->INITIALIZE)( "trade", "sbroker", "quit" );
        /* open the portfolio table */
        chdir( dir );
        wattach( table );
        for ( row = 1 ;( row ); row = nextrow() ) {
                shares = model( current_portfolio_value, table.* );
                if ( !shares ) continue;
                trade( sprintf( "%s,%s", table.stock, shares ));

        }
        (model->DISCARD)();
        (broker->DISCARD)();
        wdetach();
        return();
}


Example 1: (a) sample .proplist file; (b) RPI-generated additions 
to the .proplist file 

(a)
 
TABLE {'student' 'enroll' 'professors' 'course' 'dept'}
STUDENT {'stu_id' 'lastname' 'major' 'stu_desc'}
SERVERS {'sql_app' 'filexfer' 'syb2eos' 'eos2syb'}
MIPS 144
DISK 1000000000
AUTH {'Pete' 'Lowell' 'Geoff' 'Andrew' 'Kyle' 'Clark'}

(b)
 
HOST 'ferrari'
hostname 'ferrari.lri.com'
binding '187.95.103.78[1234]'
SECPAC '211'


Example 2: Client initialization 
 
foo->PROPV[ 0 ] = "(student in TABLES) or (enroll in TABLES)";
foo->PROPV[ 1 ] = "sql_app in sblist";
foo->PROPV[ 2 ] = "MIPS > 50";
foo->PROPC = 3;
 


Example 3: Command-line prompt
 
% sbroker
broker=> set stock IBM

stock set to IBM
broker=> set shares +20
order set to buy 20
broker=> execute
placing order to buy 20 shares IBM
broker=> quit