Mesquite Software : Documentation : C++ Guide : Sample Program

A sample CSIM program follows. This program is a model of an M/M/1 queueing system. The process sim includes a for loop, which generates, at appropriate intervals (exponentially distributed with mean IATM) arriving customers. These customers contend for the facility on a first-come-first-served basis. As each customer gains exclusive use of the facility, they delay for a service period (again exponentially distributed, but with mean SVTM) and then depart. The individual response times (time of arrival to time of departure) are collected in a table. The program also makes use of the histogram feature to collect the frequency distribution of the queue length.

Sample Program to Simulate Single Server Facility

// C++/CSIM Model of M/M/1 queue

#include "cpp.h" // class definitions
#include <stdio.h>

#define NARS 5000#define IAR_TM 2.0#define SRV_TM 1.0

event *done; // pointer to event done
facility *f; // pointer to facility f
table *tbl; // pointer to table of response times
qtable *qtbl; // pointer to qtable of number in system
int cnt; // count of remaining processes
FILE *fp;

void init();
void generateCustomers();
void customer();

extern "C" void sim(int argc, char *argv[]) { init(); create("sim"); generateCustomers(); done->wait(); // wait for last customer to depart report(); // model report mdlstat(); // model statistics }

void generateCustomers()
{ create("gen"); for(int i = 1; i <= NARS; i++) { hold(exponential(IAR_TM)); // interarrival intervalcustomer();// generate next customer } }

void customer() // arriving customer { double t1; create("cust");t1 = clock; // record start timeqtbl->note_entry(); // note arrivalf->reserve(); // reserve facilityhold(exponential(SRV_TM)); // service intervalf->release(); // release facilitytbl->record(clock - t1); // record response timeqtbl->note_exit(); // note departure if(--cnt == 0) done->set(); // if last customer, set event done }

void init() { fp = fopen("csim.out", "w"); set_output_file(fp);set_model_name("M/M/1 Queue"); done = new event("done"); // instantiate event done f = new facility("facility"); // instantiate facility f tbl = new table("resp tms"); // instantiate table qtbl = new qtable("num in sys") ; // instantiate qtable qtbl->add_histogram(10, 0, 10); // add histogram to qtable cnt = NARS; // initialize counter }