MESSAGE
| DATE | 2015-04-01 |
| FROM | Ruben Safir
|
| SUBJECT | Subject: [NYLXS - HANGOUT] omp pthread madness
|
[This mail was also posted to comp.unix.programmer.]
I'm doing this test program with OMP threads and I'm getting a very odd
result which I have no idea where this is happening.
i set up a shared workspace for the threads called wordspace[MAX_SPACE]
and what should happen is that it gets filled with coordinate points. PI
can be estimated by a formula based on how many at random as they are
picked, end up within a circle.
When I construct it without threads, it does a decent job of predicting
about 3.14 etc.
With OMP, it is giving numbers in the 6 zone. I don't see anything that
would make my random selection change, nor do I see anything else, so I'm
at a loss, and admittedly can use some mentoring here, not only to
understand my mistake, but to understand the theory so I don't repeat it.
pi_lib.h
#ifndef MONTI_PI
#define MONTI_PI
#define MEMORY_SPACE 10000
struct point{
double x;
double y;
};
struct point * random_point(void);
double calc_pi(void);
int count_inside(void);
#endif
pid_lib.c
/* Question 4.18 from the operating systems HW from Text
* OS Ed 9
* Class Operating SYstems at LIU
* Prog M Ghriger
*
* Ruben Safir - Student
* ********************************************************/
#include
#include
#include "pi_lib.h"
#include
#include
struct point workspace[MEMORY_SPACE];
long seed = 0;
long inside_the_circle = 0;
struct timespec ts;
struct point sample;
struct point * random_point(void)
{
int i;
double x,y;
if(seed == 0){
clock_gettime(CLOCK_REALTIME, &ts);
seed = ts.tv_nsec;
srand(seed);
}
for (i = 0; i < MEMORY_SPACE; i++){
//fprintf( stderr, "Error %d\n", __LINE__);
//x = ((double)rand()) % (double)1000000 ;
x = rand() % 1000000 ;
x = x / (double)1000000;
// printf ("x==> %F", x);
//y = ((double)rand())% (double)1000000 ;
y = rand()% 10000000 ;
y = y / (double)10000000;
// printf(" y==> %F\n", y);
workspace[i].x = x;
workspace[i].y = y;
}
return &workspace[0];
}
int count_inside(void)
{
int i = 0;
double d;
for(i = 0; i < MEMORY_SPACE; i++){
d = sqrt(pow(workspace[i].x, 2.0) + pow(workspace[i].y,
2.0));
// printf ("distance => %f\n", d);
if (d <= 1.0)
inside_the_circle++;
}
return inside_the_circle;
}
double calc_pi(){
return 4.0 * (( double)inside_the_circle/ (double)MEMORY_SPACE) ;
}
monty_pi_omp.c
#include
#include
#include "pi_lib.h"
#include
#include
void * wrapper(void*);
double pi;
int main(int argc, char * argv[]){
double pi;
#pragma omp parallel
{
random_point();
count_inside();
}
pi = calc_pi();
printf("Pi is estimated at ==> %f\n\n", pi);
return 1;
}
and just for comparison
this is monty_pi.c
#include
#include
#include "pi_lib.h"
#include
void * wrapper(void*);
int main(int argc, char * argv[]){
double pi;
pthread_attr_t attr;
pthread_attr_init(&attr);
pthread_t tid;
void * arg = NULL;
pthread_create(&tid, &attr, wrapper, arg);
pthread_join(tid, NULL);
pi = calc_pi();
printf("Pi is estimated at ==> %f\n\n", pi);
return 1;
}
void * wrapper(void * arg){
random_point();
count_inside();
pthread_exit(arg);
}
and this was the makefile
XX:=gcc
CXXFLAGS:=-Wall -g -pg
LDFLAGS:= -pg -pthread -fopenmp
monty_pi_omp : monty_pi_omp.o pi_lib.o
$(CXX) $(CXXFLAGS) $(LDFLAGS) -o monty_pi_omp.exe monty_pi_omp.o
pi_lib.o
monty_pi : monty_pi.o pi_lib.o
$(CXX) $(CXXFLAGS) $(LDFLAGS) -o monty_pi.exe monty_pi.o pi_lib.o
monty_pi_omp.o : monty_pi_omp.c pi_lib.h
$(CXX) $(CXXFLAGS) $(LDFLAGS) -c monty_pi_omp.c
monty_pi.o : monty_pi.c pi_lib.h
$(CXX) $(CXXFLAGS) $(LDFLAGS) -c monty_pi.c
pi_lib.o : pi_lib.h pi_lib.c
$(CXX) $(CXXFLAGS) $(LDFLAGS) -c pi_lib.c
include make.deps
make.deps: *.c; ${CXX} ${CXXFLAGS} -M *.c >$-at-
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