对于我的作业，我们给了一个程序，该程序可以在C语言中模拟FCFS调度算法，我们将对其进行两次修改以模拟SJF和RR（Quantum 4），并比较每个算法的平均响应时间。我已经完成了SJF版本，但是RR版本存在问题。当我使用输入4-> 1-> 10000000-> 5（这是我们要做的分配）运行时，RR的平均响应时间明显比其他输入响应时间大得多（这显然是不正确的）。有人可以帮我找出如何在我的程序中准确计算RR模拟的平均响应时间吗？我已经包括了整个程序，因此可以运行。
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <values.h>
/* simulation events */
#define ARRIVAL 0 /* arrival to queue */
#define COMPLETE 1 /* completion of service */
#define EOS 2 /* end of simulation */
/* programming constants */
#define FALSE 0
#define TRUE 1
#define DEBUG 0 /* set to 1 to turn debugging output on */
/* event list - which is a doubly linked list */
struct event_node{
int ev_type; /* event type */
long int ev_time; /* time for event to occur */
struct Custs *cust_index; /* customer responsible for this event */
struct event_node *forward; /* forward link */
struct event_node *backward; /* backward link */
} ;
struct event_node *top_event; /* points to head of event list */
struct event_node *last_event; /* points to end of event list */
/* customer nodes */
struct Custs{
long int arrive_time; /* arrival time of customer */
long int CPU_time; /* CPU burst time of customer */
long int OG_CPU_time; /* the original CPU burst time of customer (before decrease due to ) */
long int start; /* the beginning time of the first burst for each customer */
};
/* queue - simple linked list */
struct Queue {
struct Custs *cust_index; /* index of customer in the queue */
struct Queue *next; /* points to the next node in the queue */
};
struct Queue_struct {
struct Queue *q_head; /* points to top of queue */
struct Queue *q_last; /* points to bottom of queue */
};
struct Queue_struct rr;
/* statistics gathering variables */
float accum_resp_time; /* accumulate customer response time */
float num_resp_time; /* total number of custs in system */
/* input parameters */
float iarrive_time; /* mean interarrival time */
float service_time; /* mean service time */
long int sim_length; /* length of simulation */
/* system variables */
long int clock; /* simulation clock */
int busy; /* flag indicating if server is busy */
unsigned seed; /* seed for random num generator */
/* function declarations */
void arrive(struct event_node *ev_num);
void depart(struct event_node *ev_num);
void start_service(void);
void Gen_arrival(void);
void Gen_departure(struct Custs *index);
void Read_parms(void);
void Process_statistics(void);
void Initialize(void);
void Insert_event(int etype, long int etime, struct Custs *custind);
struct event_node *Remove_event(void);
void Puton_queue(struct Queue_struct *pqueue, struct Custs *pcust);
struct Custs *Takoff_queue(struct Queue_struct *pqueue);
long int expon(float time);
/*********************************************************************/
/* Name: main */
/* Description */
/* This function performs the main control loop of the simulation.*/
/* It performs the following steps: */
/* 1 - call routines to initialize global variables. */
/* 2 - schedules an end of simulation. */
/* 3 - generates the first arrival. */
/* 4 - processes the events on the event list until the end of */
/* simulation event i reached. */
/* 5 - frees event node after it has been processed. */
/* 6 - prints out the statistics when the simulation is finished. */
/*********************************************************************/
void main()
{
int not_done;
struct event_node *event;
/* initialization */
Initialize();
Read_parms();
/* schedule an end of simulation */
Insert_event(EOS, sim_length, NULL);
/* generate first arrival */
Gen_arrival();
/* main loop to process the event list */
not_done = TRUE;
while(not_done)
{
/* get next event */
event = Remove_event();
/* update clock */
clock = event->ev_time;
/* process event type */
switch (event->ev_type)
{
case ARRIVAL : arrive(event);
break;
case COMPLETE : depart(event);
break;
case EOS : Process_statistics();
not_done = FALSE;
break;
default : printf("***Error - invalid event type\n");
}
/* free event node by marking it unused */
free(event);
}
}
/*********************************************************************/
/* Name: arrive */
/* Description */
/* This function processes an arrival to the system. */
/* It performs */
/* the followiong steps: */
/* 1 - generates the next arrival. */
/* 2 - sets the system statistics. */
/* 3 - puts the customer into the queue. */
/* 4 - if the server is not busy then calls start_service. */
/**********************************************************************/
void arrive(struct event_node *ev_num)
{
struct Custs *index;
/* generate the next arrival */
Gen_arrival();
/* set statistics gathering variable */
index = ev_num->cust_index;
index->arrive_time = clock;
/* generate "random" CPU burst time for customer */
index->CPU_time = expon(service_time);
index->OG_CPU_time = index->CPU_time;
/* put the customer n the queue */
Puton_queue(&rr, index);
/* if server is not busy then start service */
if(!busy)
start_service();
return;
}
/**************************************************************/
/* Name: start_service */
/* Description */
/* This function performs the following steps: */
/* 1 - removes the first customer from the queue. */
/* 2 - sets the server to busy. */
/* 3 - schedules a departure event. */
/**************************************************************/
void start_service(void)
{
struct Custs *index;
/* remove the first customer from the queue */
index = Takoff_queue(&rr);
/* if it is the first burst for the customer... */
if(index->CPU_time == index->OG_CPU_time){
index->start = clock; // store initial service start time
}
/* set server to busy */
busy = TRUE;
/* if the CPU burst time is still greater than or equal to the Quantum 4... */
if(index->CPU_time >= 4){
index->CPU_time = index->CPU_time - 4; // subtract quantum to simulate a single burst
}
/* if the CPU burst time is less than the Quantum 4... */
if(index->CPU_time < 4){
index->CPU_time = 0; // subtract remaining CPU burst time to represent final burst
}
/* if the customer still has remaining CPU burst after previous burst... */
if(index->CPU_time >= 4){
busy = FALSE; // end burst
Puton_queue(&rr, index); // put back on the queue
return;
}
/* schedule a departure event */
Gen_departure(index);
return;
}
/********************************************************************/
/* Name: depart */
/* Description */
/* This function processes a departure from the server event. It */
/* performs the following steps: */
/* 1 - sets the server to idle. */
/* 2 - accumulate response time statistics. */
/* 3 - remove the customer from the system. */
/* 4 - if the queue is not empty, then start service. */
/********************************************************************/
void depart(struct event_node *ev_num)
{
struct Custs *index;
long int temp;
/* set server to idle */
busy = FALSE;
/* accumulate response time */
index = ev_num->cust_index;
temp = index->start - index->arrive_time;
#if DEBUG
printf(" Response time for customer is %d\n", temp);
#endif
accum_resp_time += temp; num_resp_time++;
/* remove customer from the system */
free(index);
/* if queue is non-empty, start service */
if(rr.q_head != NULL)
start_service();
return;
}
/*********************************************************************/
/* Name: Gen_arrival */
/* Description */
/* This function will generate a new arrival. It has one parameter, */
/* stream, which is the random number generator stream to be used.It */
/* performs the following steps: */
/* 1 - gets a new customer. */
/* 2 - generates an exponential arrival time. */
/* 3 - inserts arrival event into the event list. */
/*********************************************************************/
void Gen_arrival(void)
{
long int time;
struct Custs *index;
/* get new customer */
index = (struct Custs *) malloc(sizeof(struct Custs));
/* generate exponential interarrival time */
time = expon(iarrive_time);
#if DEBUG
printf(" Interarrival time for customer is %d\n", time);
printf(" Arrival time for customer is %d\n", clock + time);
#endif
/* add the event to the list */
Insert_event(ARRIVAL, clock+time, index);
return;
}
/*********************************************************************/
/* Name: Gen_departure */
/* Description */
/* This function generates a departure event from the server. It */
/* has two parameters: 1) stream - random number generator stream, */
/* and 2) index - index of customer departing. The following */
/* steps are performed: */
/* 1 - generate the service time. */
/* 2 - insert the departure event into the event list. */
/*********************************************************************/
void Gen_departure(struct Custs *index)
{
long int time;
/* generate exponential service time */
time = expon(service_time);
#if DEBUG
printf(" Service time for customer is %d\n", time);
printf(" Departure time for customer is %d\n", clock + time);
#endif
/* add departure event to the event list */
Insert_event(COMPLETE, time+clock, index);
return;
}
/**************************************************************/
/* Name: Read_parms */
/* Description */
/* This function inputs the required simulation parameters.*/
/**************************************************************/
void Read_parms(void)
{
printf(" SIMULATION -- M/M/1 Queueing System\n");
printf(" Input the following parameters:\n");
printf(" mean interarrival time => ");
scanf("%e", &iarrive_time);
printf(" mean service time => ");
scanf("%e", &service_time);
printf(" length of simulation => ");
scanf("%ld", &sim_length);
printf(" seed for the random number generator => ");
scanf("%d", &seed);
/* initialize random number generator */
srand(seed);
printf(" Simulation time = %ld units\n", sim_length);
printf(" Simulation begins...\n");
}
/*********************************************************************/
/* Name: Process_statistics */
/* Description */
/* This function computes and prints the mean response time for the */
/* customers in an M/M/1 system. */
/*********************************************************************/
void Process_statistics(void)
{
printf("accum_resp_time = %-6.3f\n", accum_resp_time);
printf("num_resp_time = %-6.3f\n", num_resp_time);
float mean_resp_time;
/* compute mean response time */
mean_resp_time = accum_resp_time / (float) (100.0 * num_resp_time);
/* print out results */
printf("...Simulation ends\n");
printf(" Simulation results\n");
printf(" mean response time ---------> %-6.3f\n", mean_resp_time);
}
/*********************************************************************/
/* Name: Initialize */
/* Description */
/* This function initializes the event list, queue, customer list, */
/* and global variables. */
/*********************************************************************/
void Initialize(void)
{
/* initialize the event list */
top_event = NULL;
last_event = NULL;
/* initialize the queue */
rr.q_head = NULL;
rr.q_last = NULL;
/* initialize the global variables */
clock = 0;
busy = FALSE;
accum_resp_time = 0;
num_resp_time = 0;
}
/*********************************************************************/
/* Name: Insert_event */
/* Description */
/* This procedure will insert the simulation event into a doubly */
/* linked queue. The parameters are as follows: */
/* etype - type of event to be inserted. */
/* etime - the time the event will occur. */
/* custind - index of the customer associated with this event. */
/* The following steps are performed: */
/* 1 - get a free node and add the event information. */
/* 2 - insert node into the proper place in the queue. */
/* 2a - into an empty queue. */
/* 2b - at the top of the queue. */
/* 2c - at the bottom of the queue. */
/* 2d - regular insertion (someplace in the middle). */
/*********************************************************************/
void Insert_event(int etype, long int etime,struct Custs *custind)
{
int not_found;
struct event_node *loc, *pos;
loc = (struct event_node *) malloc(sizeof (struct event_node));
/* add the information to the structure */
loc->ev_type = etype;
loc->ev_time = etime;
loc->cust_index = custind;
loc->forward = NULL;
loc->backward = NULL;
/* determine if the list is empty */
if(top_event == NULL)
{
top_event = loc;
last_event = loc;
return;
}
/* see if it belongs on top */
if(top_event->ev_time > etime)
{
top_event->backward = loc;
loc->forward = top_event;
top_event = loc;
return;
}
/* see if it belongs at the bottom */
if(last_event->ev_time <= etime)
{
last_event->forward = loc;
loc->backward = last_event;
last_event = loc;
return;
}
/* it belongs somewhere in the middle so find its place */
not_found = TRUE;
pos = top_event;
while(pos != NULL && not_found)
{
if(pos->ev_time > etime)
not_found = FALSE;
else
pos = pos->forward;
}
/* check to see if we found something as we should have */
if(not_found)
{
printf(" ***Error - problems in insert event routine***\n");
return;
}
/* add node to appropriate place */
loc->forward = pos;
loc->backward = pos->backward;
(pos->backward)->forward = loc;
pos->backward = loc;
return;
}
/*********************************************************************/
/* Name: Remove_event */
/* Description */
/* This function returns the next event from the head of the */
/* event list. It checks for a special case where there is only */
/* one event so the event list can be marked empty. */
/*********************************************************************/
struct event_node *Remove_event(void)
{
struct event_node *ev_ptr;
/* check to see if event list is empty */
if(last_event == NULL)
{
printf(" ***Error - Event list underflow***\n");
return(NULL);
}
/* remove top element */
ev_ptr = top_event;
/* see if it was the only event - special case to mark empty */
if(top_event == last_event)
{
top_event = NULL;
last_event = NULL;
return(ev_ptr);
}
/* event list has more than one element so just relink */
top_event = top_event->forward;
top_event->backward = NULL;
ev_ptr->forward = NULL;
return(ev_ptr);
}
/*********************************************************************/
/* Name: Puton_queue */
/* Description */
/* This procedure inserts a customer at the end of the given */
/* queue. The parameters are as follows: */
/* pqueue - pointer to the queue. */
/* pcust - index of the customer to be inserted. */
/* The procedure performs the following steps: */
/* 1 - get a free node for the customer. */
/* 2 - inset the node ar the end of the queue. */
/* 2a - into an empty queue */
/* 2b - normal insertion */
/*********************************************************************/
void Puton_queue(struct Queue_struct *pqueue, struct Custs *pcust)
{
struct Queue *newnode;
/* get an new node */
newnode = (struct Queue *) malloc(sizeof(struct Queue));
/* now loc is the index of a free node in queue */
/* put information in the node */
newnode->cust_index = pcust;
newnode->next = NULL;
/* check to see if the queue is initially empty */
if(pqueue->q_last == NULL)
{
pqueue->q_head = newnode;
pqueue->q_last = newnode;
return;
}
/* otherwise add it to the end of the queue and relink */
pqueue->q_last->next = newnode;
pqueue->q_last = newnode;
return;
}
/*********************************************************************/
/* Name: Takoff_queue */
/* Description */
/* This function returns the index into the customer array of */
/* the head element of the given queue. The parameters are: */
/* pqueue - pointer to the given queue. */
/* If the customer removed is the last remaining customer, the */
/* queue is marked empty. */
/*********************************************************************/
struct Custs *Takoff_queue(struct Queue_struct *pqueue)
{
struct Queue *loc;
struct Custs *index;
/* check if the queue is empty */
if(pqueue->q_head == NULL)
{
printf(" ***Error - queue underflow***\n");
return(NULL);
}
/* remove top element from queue */
loc = pqueue->q_head;
/* get customer index */
index = loc->cust_index;
/* check if queue now empty and relink */
if(pqueue->q_head == pqueue->q_last)
{
pqueue->q_last = NULL;
pqueue->q_head = NULL;
return(index);
}
/* otherwise just relink */
pqueue->q_head = loc->next;
free(loc);
return(index);
}
/*********************************************************************/
/* Name: expon */
/* Description */
/* This function is used to generate an exponential variate given */
/* the mean time. */
/*********************************************************************/
long int expon(float time)
{
long int val;
double temp;
time = time * 100;
temp = 1.0 - (rand()/ (float) RAND_MAX);
val = ceil(-time * log((double) temp));
return(val);
}
转换问题导致不确定的行为。
注意：这可能会解决OP的问题，也可能无法解决，但肯定是需要解决的问题。
下面可能会导致log((double) 0.0)，并尝试将无穷大转换为long。
temp = 1.0 - (rand()/ (float) RAND_MAX);
val = ceil(-time * log((double) temp));
在RAND_MAX = 32767的系统上，这很可能。
备用代码
#include <limits.h>
long int expon(float time) {
time = time * 100;
// temp = 1.0 - (rand()/ (float) RAND_MAX);
double temp = 1.0 - (rand()/ (RAND_MAX + 1.0));
assert(temp > 0);
double dval = ceil(-time * log(temp));
assert(dval >= LONG_MIN && dval < (LONG_MAX/2 + 1)*2.0);
return (long) dval;
}
我的结果是
Simulation time = 10000000 units
Simulation begins...
accum_resp_time = 2582940416.000
num_resp_time = 1443.000
...Simulation ends
Simulation results
mean response time ---------> 17899.795
代码在float与double混合数学中起着很大的作用。我建议将所有float对象移到double。