Hello all,
I have a program in which 2 threads write data to a pvfs2 fs using the
writev function. I am seeing an incorrect file size after the writes are
done.
This is what the program does:
- Spawn 2 threads using OpenMP. Thread0 will write to file test1.out,
thread1 will write to file test2.out
- In a single writev call, each thread writes an iovec array of 512
elements, each element of size 1M. So a single writev call writes 512M
data. This cycle is performed twice in total, so each thread writes a
file of size 1G.
Once the program finishes, I see that the two files created are of size
512M each, instead of 1G. I ran this program on a local hard drive, and
it works fine.
I have attached the program here. Any help is appreciated.
Regards,
Kshitij Mehta
PhD candidate
Parallel Software Technologies Lab
Dept. of Computer Science
University of Houston
Houston, Texas, USA
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <sys/time.h>
#include <sys/uio.h>
#include <unistd.h>
#include <errno.h>
#include <omp.h>
int seg_rows, DEBUG, num_threads; //num_threads to be ignored for this program
double total_size, t1, t2;
long seg_size;
char* filename;
void omp_write_sep();
typedef struct _LL
{
char *str;
struct _LL* next;
} LL;
void create_ll(LL** head)
{
int i;
LL* prev = NULL;
for (i=0; i<seg_rows; i++)
{
LL *tmpll = (LL *) malloc (sizeof(LL));
tmpll->str = (char*) malloc (seg_size * sizeof(char));
tmpll->next = NULL;
if(i==0)
*head = tmpll;
else
prev->next = tmpll;
prev = tmpll;
}
}
void create_iovec(struct iovec ** iovarr, LL* head)
{
*iovarr = (struct iovec *) malloc (seg_rows * sizeof(struct iovec));
int i;
LL* iterator = head;
for (i=0; i<seg_rows; i++)
{
(*iovarr)[i].iov_base = iterator->str;
(*iovarr)[i].iov_len = seg_size;
iterator = iterator->next;
}
}
int main(int argc, char** argv)
{
//initialize some variables
DEBUG = 1; //enable printing
num_threads = 2;
total_size = 2147483648; //2GB
seg_size = 1048576; //1MB
seg_rows = 512;
omp_write_sep();
return 0;
}
void omp_write_sep()
{
int iter, i;
iter = total_size/(num_threads*seg_rows*seg_size);
#pragma omp parallel default(shared) private(i)
{
int fd;
LL* my_ll;
create_ll (&my_ll);
struct iovec* iovarr;
create_iovec (&iovarr, my_ll);
if(omp_get_thread_num() == 0)
filename="/pvfs2/test1.out";
else
filename="/pvfs2/test2.out";
if(-1 == (fd = open(filename, O_RDWR|O_CREAT, 0644)))
{
fprintf(stderr, "Error opening file. Exiting..\n");
exit(-1);
}
for(i=0; i<iter; i++)
{
if(DEBUG)
{
printf("T%d iter %d\n", omp_get_thread_num(),
i);
printf("T%d wrote %ld bytes\n",
omp_get_thread_num(), writev(fd, iovarr, seg_rows));
}
else
writev(fd, iovarr, seg_rows);
} //omp for
fsync(fd);
close(fd);
} //omp parallel
}
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