data race check with valgrind

http://valgrind.org/docs/manual/hg-manual.html

/* * gcc t.c -o t -g -lpthread * valgrind --tool=helgrind ./t */#include <pthread.h>int var = 0;void* child_fn ( void* arg ) {   var++; /* Unprotected relative to parent */ /* this is line 6 */   return NULL;}int main ( void ) {   pthread_t child;   pthread_create(&child, NULL, child_fn, NULL);   var++; /* Unprotected relative to child */ /* this is line 13 */   pthread_join(child, NULL);   return 0;}