pthread_test/insanesync.cc

   1 #include <stdlib.h>
   2 #include <stdio.h>
   3 #include <pthread.h>
   4 #include <atomic>
   5
   6 #include "librace.h"
   7 #include "model-assert.h"
   8
   9 using namespace std;
  10
  11 atomic_int x, y;
  12 atomic_intptr_t z, z2;
  13
  14 int r1, r2, r3; /* "local" variables */
  15
  16 /**
  17                 This example illustrates a self-satisfying cycle involving
  18                 synchronization.  A failed synchronization creates the store that
  19                 causes the synchronization to fail.
  20
  21                 The C++11 memory model nominally allows r1=0, r2=1, r3=5.
  22
  23                 This example is insane, we don't support that behavior.
  24 */
  25
  26
  27 static void *a(void *obj)
  28 {
  29         z.store((intptr_t)&y, memory_order_relaxed);
  30         r1 = y.fetch_add(1, memory_order_release);
  31         z.store((intptr_t)&x, memory_order_relaxed);
  32         r2 = y.fetch_add(1, memory_order_release);
  33         return NULL;
  34 }
  35
  36
  37 static void *b(void *obj)
  38 {
  39         r3 = y.fetch_add(1, memory_order_acquire);
  40         intptr_t ptr = z.load(memory_order_relaxed);
  41         z2.store(ptr, memory_order_relaxed);
  42         return NULL;
  43 }
  44
  45 static void *c(void *obj)
  46 {
  47         atomic_int *ptr2 = (atomic_int *)z2.load(memory_order_relaxed);
  48         (*ptr2).store(5, memory_order_relaxed);
  49         return NULL;
  50 }
  51
  52 int user_main(int argc, char **argv)
  53 {
  54         pthread_t t1, t2, t3;
  55
  56         atomic_init(&x, 0);
  57         atomic_init(&y, 0);
  58         atomic_init(&z, (intptr_t) &x);
  59         atomic_init(&z2, (intptr_t) &x);
  60
  61         pthread_create(&t1,NULL, &a, NULL);
  62         pthread_create(&t2,NULL, &b, NULL);
  63         pthread_create(&t3,NULL, &c, NULL);
  64
  65         pthread_join(t1,NULL);
  66         pthread_join(t2,NULL);
  67         pthread_join(t3,NULL);
  68
  69         printf("r1=%d, r2=%d, r3=%d\n", r1, r2, r3);
  70
  71         return 0;
  72 }