#include <stdio.h>

#include <stdlib.h>

#include <pthread.h>

#define N 4

int A[N][N];



int total = 0;          // global total

pthread_mutex_t *m;     // mutex pointer

void *func(void *arg)   // working thread function

{

    int i, row, sum = 0;

    pthread_t tid = pthread_self();     // get thread ID number

    row = (int)arg;                     // get row number from arg

    printf ("Thread %d [%lu] computes sum of row %d\n", row, tid, row);

    for (i=0; i<N; i++)                 //compute partial sum of A[ row ]in

        sum += A[row][i];

    printf("Thread %d [%lu] update total with %d : ", row, tid, sum);

    pthread_t mutx_lock(m);

        total += sum;                   // update global total inside a CR

    pthread_mutex_unlock(m);

    printf("total = %d\n", total);

}



int main (int argc, char *argv[])

{

    pthread_t thread[N];

    int i, j, r, sum[10];

    void *status;

    printf("Main: initialize A matrix\n");

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

        sum[i] = 0;

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

            A[i][j] = i*N + j + 1;

            printf("%4d ", A[i][j]);

        }

        printf("\n");

    }

    // create a mutex m

    m = (pthread_mutex_t *)malloc(sizeof(pthread_mutex_t));

    pthread_mutex_init(m, NULL);    // initialize mutex m

    printf("Main: create %d threads\n", N);

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

        pthread_create(&thread[i], NULL, func, (void *)i);

    }

    printf("Main: try to join with threads\n");

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

        pthread_join(thread[i], &status);

        printf("Main: joined with %d [%lu]: status=%d\n",

                i, thread[i], (int)status);

    }

    printf("Main: tatal = %d\n", total);

    pthread_mutex_destroy(m);       // destroy mutex m

    pthread_exit(NULL);

}