Question

modify the code for timer_test_02.c to allow the time delay between events to be pseudo-

random exponential, with a mean time between arrivals of 0.1 second. Change the limit in the time_stamps() function from 5 time-stamps to 10, so that the mean run-time will be about 10*0.1 = 1.0 seconds. Once this is working, you should be able to generate 10 events with a pseudo-random exponential arrival process.

The code is:

#include <stdio.h>

#include <stdint.h>

#include <time.h>

#include <unistd.h>

#include <sys/types.h>

#include <unistd.h>

struct timespec start, end;

/* A user function to extract the number of nanoseconds that have elapsed*/

int64_t timespecDiff(struct timespec*, struct timespec*);

/* The time_stamps() process is encapsulated into a function */

int time_stamps(pid_t);

int main(void)

{

int r_val;

pid_t PID ;

PID = getpid();

r_val = time_stamps(PID);

return r_val;

}

int64_t timespecDiff(struct timespec *timeA_p, struct timespec *timeB_p)

{

return ((timeA_p->tv_sec * 1000000000) + timeA_p->tv_nsec) -

((timeB_p->tv_sec * 1000000000) + timeB_p->tv_nsec);

}

int time_stamps(pid_t PID){

/* A process that prints out a process ID, and time-stamps */

int k = 0 ;

double e_time_sec ;

/* start the clock*/

clock_gettime(CLOCK_MONOTONIC, &start);

/* Some code we are interested to measure time elapsed*/

for (k=0;k<5;k++)

{

usleep(100000);

clock_gettime(CLOCK_MONOTONIC, &end);

uint64_t timeElapsed = timespecDiff(&end, &start);

e_time_sec = ((double) timeElapsed) * 1.0E-9;

printf("PID: %d \t e_time: %E\n", PID, e_time_sec);

}

return 0;

}

Answer 1

#include <stdio.h>

#include <stdlib.h>

#include <stdint.h>

#include <time.h>

#include <unistd.h>

#include <sys/types.h>

#include <unistd.h>

#include <math.h>

struct timespec start, end;

/* A user function to extract the number of nanoseconds that have elapsed*/

int64_t timespecDiff(struct timespec*, struct timespec*);

/* The time_stamps() process is encapsulated into a function */

int time_stamps(pid_t);

double ran_expo(double lambda){

double u;

u = rand() / (RAND_MAX + 1.0);

return -log(1- u) / lambda;

}

int main(void)

{

int r_val;

pid_t PID ;

PID = getpid();

time_t t;

srand((unsigned) time(&t));

r_val = time_stamps(PID);

return r_val;

}

int64_t timespecDiff(struct timespec *timeA_p, struct timespec *timeB_p)

{

return ((timeA_p->tv_sec * 1000000000) + timeA_p->tv_nsec) -

((timeB_p->tv_sec * 1000000000) + timeB_p->tv_nsec);

}

int time_stamps(pid_t PID){

/* A process that prints out a process ID, and time-stamps */

int k = 0 ;

double e_time_sec ;

/* start the clock*/

clock_gettime(CLOCK_MONOTONIC, &start);

/* Some code we are interested to measure time elapsed*/

for (k=0;k<10;k++)

{

double r = ran_expo(0.1);

// printf("%lf\n", r);

usleep(10000 * r);

clock_gettime(CLOCK_MONOTONIC, &end);

uint64_t timeElapsed = timespecDiff(&end, &start);

e_time_sec = ((double)timeElapsed) * 1.0E-9;

printf("PID: %d \t e_time: %E\n", PID, e_time_sec);

}

return 0;

}