tests/pthread/test_pthread_volatile.cpp

// Copyright 2015 The Emscripten Authors.  All rights reserved.
// Emscripten is available under two separate licenses, the MIT license and the
// University of Illinois/NCSA Open Source License.  Both these licenses can be
// found in the LICENSE file.

#include <pthread.h>
#include <errno.h>
#include <emscripten.h>
#include <emscripten/threading.h>

// Toggle to use two different methods for updating shared data (C++03 volatile vs explicit atomic ops).
// Note that using a volatile variable explicitly depends on x86 strong memory model semantics.
//#define USE_C_VOLATILE

volatile int sharedVar = 0;

static void *thread_start(void *arg) // thread: just flip the shared flag and quit.
{
#ifdef USE_C_VOLATILE
  sharedVar = 1;
#else
  emscripten_atomic_store_u32((void*)&sharedVar, 1);
#endif
  pthread_exit(0);
}

int main()
{
  int result;
  if (!emscripten_has_threading_support())
  {
#ifdef REPORT_RESULT
    REPORT_RESULT(1);
#endif
    printf("Skipped: Threading is not supported.\n");
    return 0;
  }

  pthread_t thr;
  int rc = pthread_create(&thr, NULL, thread_start, (void*)0);
  if (rc != 0)
  {
#ifdef REPORT_RESULT
    int result = (rc != EAGAIN);
    REPORT_RESULT(result);
    return 0;
#endif
  }

#ifdef USE_C_VOLATILE
  while(sharedVar == 0)
    ;
#else
  while(emscripten_atomic_load_u32((void*)&sharedVar) == 0) {}
#endif

#ifdef REPORT_RESULT
  REPORT_RESULT(sharedVar);
#endif
}