helgrind/tests/hg03_inherit.c

   1
   2 /* I don't think this is a very good test .. all this
   3    sleepery is highly confusing. */
   4
   5 /* test child thread inheriting data */
   6
   7 #include <stdio.h>
   8 #include <pthread.h>
   9 #include <unistd.h>
  10
  11 static volatile int shared[2];
  12
  13 static void *t1(void *v)
  14 {
  15         volatile int *ip = (int *)v;
  16         if (0) printf("ta W\n");
  17         *ip += 44;
  18         *ip *= 2;
  19         sleep(1);
  20         return 0;
  21 }
  22
  23 static void *t2(void *v)
  24 {
  25         volatile int *ip = (int *)v;
  26         sleep(2);
  27         if (0) printf("tb W\n");
  28         *ip += 88;
  29         *ip *= 3;
  30         sleep(1);
  31         return 0;
  32 }
  33
  34 int main(void)
  35 {
  36         pthread_t a, b;
  37         volatile int ret = 0;
  38
  39         sleep(0);
  40
  41         shared[0] = 22;
  42         shared[1] = 77;
  43
  44         pthread_create(&a, NULL, t1, (void *)&shared[0]);
  45         // a steals shared[0] from root thread, so is excl(a)
  46         pthread_create(&b, NULL, t2, (void *)&shared[1]);
  47         // b steals shared[1] from root thread, so is excl(b)
  48
  49         pthread_join(a, NULL);
  50         // b's stuff (shared[1]) still belongs to b, so is excl(b)
  51
  52         // ret is excl(root), and shared[0] is re-acquired as excl(root)
  53         // since a joined to root
  54         if (0) printf("r R1\n");
  55         ret += shared[0];       /* no error - a is finished */
  56
  57         // but shared[1] is excl(b); hence we're reading excl(b)
  58         // without a lock and without a dependency edge
  59         if (0) printf("r R2\n");
  60         ret += shared[1];       /* expect error - b has not finished,
  61                                    so we can't touch shared[1] yet */
  62
  63         pthread_join(b, NULL);
  64
  65
  66         return ret;
  67 }