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
/* simulate an M/M/1 queue
(an open queue with exponential service
times and interarrival intervals)
*/
#include csim.h
#include <stdio.h>
#define SVTM 1.0 /*
mean of service time distribution */
#define IATM 2.0 /* mean of inter-arrival
time distribution */
#define NARS 5000 /* number of arrivals
to be simulated*/
FACILITY f; /* pointer
for facility */
EVENT done; /* pointer for counter */
TABLE tbl; /* pointer for table */
QTABLE qtbl; /* pointer for qhistogram
*/
int cnt; /* number of active tasks*/
FILE *fp;
void init();
void generateCustomers();
void cust();
void sim() /* 1st process
- named sim */
{
init(); /* initialize
file, model */
create(sim); /* required create statement
*/
generateCustomers(); /* invoke process
to generate customers */
wait(done); /* wait until all done */
report(); /* print report */
mdlstat(); /* print operational statistics
*/
}
void generateCustomers()
{
int i;
create(gen); /* create
statement */
for(i = 1; i <= NARS; i++) {
hold(exponential(IATM));
/* hold interarrival */
cust(); /* initiate process cust */
}
}
void cust() /* process
customer */
{
TIME t1;
create(cust); /* create statement */
t1 = clock; /* time
of arrival */
note_entry(qtbl); /* note arrival */
reserve(f); /* reserve facility f */
hold(exponential(SVTM));/* hold service
time */
release(f); /* release facility f */
record(clock-t1, tbl); /* record response
time */
note_exit(qtbl); /* note departure */
cnt--; /* decrement cnt */
if(cnt == 0)
set(done); /*if last arrival, signal
done*/
}
void init()
{
fp = fopen(csim.out,
w);
set_output_file(fp);
set_trace_file(fp);
set_error_file(fp);
set_model_name(M/M/1 Queue);
f = facility(facility);
/* initialize facility */
done = event(done); /* initialize event
*/
tbl = table(resp tms); /* initialize
table */
qtbl = qhistogram(num in sys, 10l);
/* initialize qhistogram */
cnt = NARS; /* initialize cnt */
}
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