Code samples & Admin examples – Darius Bufnea, PhD, Assoc. Prof.

Accesarea unor servicii din Campus (rețeaua privată a Departamentului de Informatică) folosind SSH tunneling

February 20, 2021Darius Bufnea

Folosind un mecanism numit SSH tunneling este posibila accesarea unor servicii, procese server, aplicatii web, etc. de oriunde din Internet si gazduite pe adrese IP private (false) din cadrul retelei Departamentului de Informatica (Campus, cladirea FSEGA). Mecanismul de SSH tunneling… Continue Reading →

Accesarea unor resurse din campus/prin intermediul rețelei din campus pe perioada pandemiei

April 14, 2020Darius Bufnea

Studenții care în această perioadă doresc să acceseze serverul linux al studenților (linux.scs.ubbcluj.ro) o pot face prin intermediul numelui www.scs.ubbcluj.ro (sau a adresei sale IP reale: 193.226.40.130), port 8937, protocol SSH, cu aplicații care suportă acest protocol (Putty, WinSCP). Use… Continue Reading →

User authentication in Java using the IMAP or SMTP protocols

March 3, 2018Darius Bufnea

Recently, a couple of students have asked me the same question: “I need to authenticate users (other students) in my diploma thesis application with their faculty credentials. Is there a way to do this?” The faculty student server (i.e. www.scs.ubbcluj.ro)… Continue Reading →

Matrix multiplication using threads

March 13, 2015Darius Bufnea

Save the following lines of code in a file called matrix_multiplication.c, then compile and run it:

$ gcc -o matrix_multiplication matrix_multiplication.c -lpthread
$ ./matrix_multiplication

1 2	$ gcc -o matrix_multiplication matrix_multiplication.c -lpthread $ ./matrix_multiplication

I would recommend running in parallel the top command in another shell window to observe the system/processors load.

#include <pthread.h>
#include <stdio.h>
#include <time.h>

// use 4 for a quad processor, but try also with 1 and 2 threads
// to check the running time and the system load
#define thread_count 4

// matrix dimension
#define dim 1500

struct param {
  int start_line, end_line;
};

int a[dim][dim], b[dim][dim], c[dim][dim];

void init_matrix(int m[dim][dim]) {
   int i, j;
   for (i = 0; i < dim; i++)
     for (j = 0; j < dim; j++)
       m[i][j] = random() % 100;
}

void* thread_function(void *v) {
  struct param *p = (struct param *) v;
  
  int i, j, k;
  for (i = p->start_line; i < p->end_line; i++)
    for (j = 0; j < dim; j++) {
      int s = 0;
      for (k = 0; k < dim; k++)
        s += a[i][k] * b[k][j];
      c[i][j] = s;
    }
}

int main() {
  int i;
  struct param params[thread_count];
  pthread_t t[thread_count];
  
  srand(getpid());
  int start_time, end_time;
  
  init_matrix(a);
  init_matrix(b);
  
  start_time = time(NULL);

  for (i = 0; i < thread_count; i++) {
    int code;
    params[i].start_line = i * (dim / thread_count);
    params[i].end_line = (i + 1) * (dim / thread_count);
    
    code = pthread_create(&t[i], NULL, thread_function, &params[i]);
    if (code != 0)
      printf("Error starting thread %d\n", i);
  }
  
  for (i = 0; i < thread_count; i++) 
    pthread_join(t[i], NULL);
  
  end_time = time(NULL);
  
  printf("Running time: %d\n", end_time - start_time);
}

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#include <pthread.h>

#include <stdio.h>

#include <time.h>

// use 4 for a quad processor, but try also with 1 and 2 threads

// to check the running time and the system load

#define thread_count 4

// matrix dimension

#define dim 1500

struct param {

int start_line, end_line;

};

int a[dim][dim], b[dim][dim], c[dim][dim];

void init_matrix(int m[dim][dim]) {

int i, j;

for (i = 0; i < dim; i++)

for (j = 0; j < dim; j++)

m[i][j] = random() % 100;

}

void* thread_function(void *v) {

struct param *p = (struct param *) v;

int i, j, k;

for (i = p->start_line; i < p->end_line; i++)

for (j = 0; j < dim; j++) {

int s = 0;

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

s += a[i][k] * b[k][j];

c[i][j] = s;

}

int main() {

int i;

struct param params[thread_count];

pthread_t t[thread_count];

srand(getpid());

int start_time, end_time;

init_matrix(a);

init_matrix(b);

start_time = time(NULL);

for (i = 0; i < thread_count; i++) {

int code;

params[i].start_line = i * (dim / thread_count);

params[i].end_line = (i + 1) * (dim / thread_count);

code = pthread_create(&t[i], NULL, thread_function, &params[i]);

if (code != 0)

printf("Error starting thread %d\n", i);

}

for (i = 0; i < thread_count; i++)

pthread_join(t[i], NULL);

end_time = time(NULL);

printf("Running time: %d\n", end_time - start_time);

}