pthread_spin_lock not working - c++

Question

I have following piece of code :
// temp.h
#include <iostream>
#include <pthread.h>
static pthread_spinlock_t mylock;
__attribute__((constructor))
void init_lock() {
if(pthread_spin_init(&my_lock,0) != 0) {
// hard exit !!
exit(1);
}
}
__attribute__((destructor))
void uninit_lock() {
if(pthread_spin_destroy(&my_lock) != 0) {
// hard exit !!
exit(1);
}
}
#define EXPAND_VAR(ARG1, ARG2) \
do {\
assert(pthread_spin_lock(&my_lock) == 0);
/// do something
assert(pthread_spin_unlock(&my_lock) == 0);\
}while(0)
// main.cpp
#include "temp.h"
#define NUM_THREADS 5
void *logs(void *i){
int j;
for(j = 0 ; j < 10000 ; j++){
EXPAND_VAR(j, j+1);
}
std::cout << "returning from thread func" << std::endl;
pthread_exit(NULL);
}
int main(int argc, char* argv[]) {
int i;
pthread_t threads[NUM_THREADS];
for( i = 0; i < NUM_THREADS; i++) {
std::cout << " creating threads" << std::endl;
rc = pthread_create(&threads[i],NULL,logs,(void *)i);
}
std::cout << "returning from main" << std::endl;
pthread_exit(NULL);
return 0;
}
When executing the above code 'pthread_spin_lock' always gets blocked. I tried 'pthread_spin_trylock' and it passes with return value 0.
Anything i am missing that 'pthread_spin_lock' not working ?
I am using gcc version 4.1.2 :(