/* -------------------------------------------------------------------------  * This program is a next-event simulation of a multi-server, single-queue  * service node.  The service node is assumed to be initially idle, no  * arrivals are permitted after the terminal time STOP and the node is then  * purged by processing any remaining jobs.  *  * Name              : msq.c (Multi-Server Queue) * Author            : Steve Park & Dave Geyer  * Language          : ANSI C  * Latest Revision   : 10-19-98  * -------------------------------------------------------------------------  */#include <stdio.h>#include <math.h>#include "rngs.h"#define START    0.0                    /* initial (open the door)        */#define STOP     20000.0                /* terminal (close the door) time */#define SERVERS  4                      /* number of servers              */typedef struct {                        /* the next-event list    */  double t;                             /*   next event time      */  int    x;                             /*   event status, 0 or 1 */} event_list[SERVERS + 1];                 double Exponential(double m)/* --------------------------------------------------- * generate an Exponential random variate, use m > 0.0  * --------------------------------------------------- */{  return (-m * log(1.0 - Random()));}   double Uniform(double a, double b)/* -------------------------------------------- * generate a Uniform random variate, use a < b  * -------------------------------------------- */{  return (a + (b - a) * Random());}   double GetArrival(void)/* --------------------------------------------- * generate the next arrival time, with rate 1/2 * --------------------------------------------- */ {       static double arrival = START;  SelectStream(0);  arrival += Exponential(2.0);  return (arrival);}      double GetService(void)/* --------------------------------------------- * generate the next service time, with rate 1/6 * --------------------------------------------- */ {                   SelectStream(1);                              return (Uniform(2.0, 10.0));    }   int NextEvent(event_list event)/* --------------------------------------- * return the index of the next event type * --------------------------------------- */{  int e;                                        int i = 0;  while (event[i].x == 0)       /* find the index of the first 'active' */    i++;                        /* element in the event list            */   e = i;                          while (i < SERVERS) {         /* now, check the others to find which  */    i++;                        /* event type is most imminent          */    if ((event[i].x == 1) && (event[i].t < event[e].t))      e = i;  }  return (e);}   int FindOne(event_list event)/* ----------------------------------------------------- * return the index of the available server idle longest * ----------------------------------------------------- */{  int s;  int i = 1;  while (event[i].x == 1)       /* find the index of the first available */    i++;                        /* (idle) server                         */  s = i;  while (i < SERVERS) {         /* now, check the others to find which   */     i++;                        /* has been idle longest                 */    if ((event[i].x == 0) && (event[i].t < event[s].t))      s = i;  }  return (s);}  int main(void){  struct {    double current;                  /* current time                       */    double next;                     /* next (most imminent) event time    */  } t;  event_list event;  long       number = 0;             /* number in the node                 */  int        e;                      /* next event index                   */  int        s;                      /* server index                       */  long       index  = 0;             /* used to count processed jobs       */  double     area   = 0.0;           /* time integrated number in the node */  struct {                           /* accumulated sums of                */    double service;                  /*   service times                    */    long   served;                   /*   number served                    */  } sum[SERVERS + 1];  PlantSeeds(0);  t.current    = START;  event[0].t   = GetArrival();  event[0].x   = 1;  for (s = 1; s <= SERVERS; s++) {    event[s].t     = START;          /* this value is arbitrary because */    event[s].x     = 0;              /* all servers are initially idle  */    sum[s].service = 0.0;    sum[s].served  = 0;  }  while ((event[0].x != 0) || (number != 0)) {    e         = NextEvent(event);                  /* next event index */    t.next    = event[e].t;                        /* next event time  */    area     += (t.next - t.current) * number;     /* update integral  */    t.current = t.next;                            /* advance the clock*/    if (e == 0) {                                  /* process an arrival*/      number++;      event[0].t        = GetArrival();      if (event[0].t > STOP)        event[0].x      = 0;      if (number <= SERVERS) {        double service  = GetService();        s               = FindOne(event);        sum[s].service += service;        sum[s].served++;        event[s].t      = t.current + service;        event[s].x      = 1;      }    }    else {                                         /* process a departure */      index++;                                     /* from server s       */        number--;      s                 = e;                             if (number >= SERVERS) {        double service   = GetService();        sum[s].service += service;        sum[s].served++;        event[s].t      = t.current + service;      }      else        event[s].x      = 0;    }  }  printf("\nfor %ld jobs the service node statistics are:\n\n", index);  printf("  avg interarrivals .. = %6.2f\n", event[0].t / index);  printf("  avg wait ........... = %6.2f\n", area / index);  printf("  avg # in node ...... = %6.2f\n", area / t.current);  for (s = 1; s <= SERVERS; s++)            /* adjust area to calculate */        area -= sum[s].service;              /* averages for the queue   */      printf("  avg delay .......... = %6.2f\n", area / index);  printf("  avg # in queue ..... = %6.2f\n", area / t.current);  printf("\nthe server statistics are:\n\n");  printf("    server     utilization     avg service        share\n");  for (s = 1; s <= SERVERS; s++)    printf("%8d %14.3f %15.2f %15.3f\n", s, sum[s].service / t.current,            sum[s].service / sum[s].served,            (double) sum[s].served / index);  printf("\n");  return (0);}