third_party/llvm-project/compiler-rt/test/tsan/annotate_happens_before.cc

// RUN: %clangxx_tsan -O1 %s -o %t && %run %t 2>&1 | FileCheck %s
#include "test.h"

/*
Annotations usage example.

Tsan does not see synchronization in barrier_wait.
ANNOTATE_HAPPENS_BEFORE/AFTER communicate the synchronization to tsan
and prevent the race report.

If the compiler does not support __has_feature macro, then you can build with
CFLAGS="-fsanitize=thread -DTHREAD_SANITIZER" and then use
#ifdef THREAD_SANITIZER to enabled annotations.
*/

#if defined(__has_feature) && __has_feature(thread_sanitizer)
# define ANNOTATE_HAPPENS_BEFORE(addr) \
    AnnotateHappensBefore(__FILE__, __LINE__, (void*)(addr))
# define ANNOTATE_HAPPENS_AFTER(addr) \
    AnnotateHappensAfter(__FILE__, __LINE__, (void*)(addr))
extern "C" void AnnotateHappensBefore(const char *f, int l, void *addr);
extern "C" void AnnotateHappensAfter(const char *f, int l, void *addr);
#else
# define ANNOTATE_HAPPENS_BEFORE(addr)
# define ANNOTATE_HAPPENS_AFTER(addr)
#endif

int Global;

void *Thread1(void *x) {
  barrier_wait(&barrier);
  ANNOTATE_HAPPENS_AFTER(&barrier);
  Global++;
  return NULL;
}

void *Thread2(void *x) {
  Global--;
  ANNOTATE_HAPPENS_BEFORE(&barrier);
  barrier_wait(&barrier);
  return NULL;
}

int main() {
  barrier_init(&barrier, 2);
  pthread_t t[2];
  pthread_create(&t[0], NULL, Thread1, NULL);
  pthread_create(&t[1], NULL, Thread2, NULL);
  pthread_join(t[0], NULL);
  pthread_join(t[1], NULL);
  fprintf(stderr, "DONE\n");
  return 0;
}

// CHECK-NOT: WARNING: ThreadSanitizer: data race
// CHECK: DONE