test/pthread/test_pthread_gcc_atomics.c

// 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 <assert.h>
#include <stdio.h>
#include <pthread.h>
#include <emscripten.h>
#include <emscripten/threading.h>

// This file tests the old GCC built-in atomic operations.
// See https://gcc.gnu.org/onlinedocs/gcc-4.6.4/gcc/Atomic-Builtins.html

#define NUM_THREADS 8

#define T int

// TEMP: Fastcomp backend doesn't implement these as atomic, so #define these to library
//       implementations that are properly atomic. TODO: Implement these in fastcomp.
#define __sync_lock_test_and_set(...) emscripten_atomic_fence()
#define __sync_lock_release(...) emscripten_atomic_fence()

#define Bool int

Bool atomic_bool_cas_u32(T *ptr, T oldVal, T newVal) {
  T old = emscripten_atomic_cas_u32(ptr, oldVal, newVal);
  return old == oldVal;
}

// Test __sync_val_compare_and_swap.
T nand_and_fetch(T *ptr, T x) {
  for (;;) {
    T old = emscripten_atomic_load_u32(ptr);
    T newVal = ~(old & x);
    T old2 = __sync_val_compare_and_swap(ptr, old, newVal);
    if (old2 == old) return newVal;
  }
}

// Test __sync_bool_compare_and_swap.
T nand_and_fetch_bool(T *ptr, T x) {
  for (;;) {
    T old = emscripten_atomic_load_u32(ptr);
    T newVal = ~(old & x);
    Bool success = __sync_bool_compare_and_swap(ptr, old, newVal);
    if (success) return newVal;
  }
}

volatile int nand_and_fetch_data = 0;
void *thread_nand_and_fetch(void *arg) {
  for (int i = 0; i < 999; ++i) { // Odd number of times so that the operation doesn't cancel itself out.
    nand_and_fetch((int*)&nand_and_fetch_data, (int)(long)arg);
  }
  pthread_exit(0);
}

void *thread_nand_and_fetch_bool(void *arg) {
  for (int i = 0; i < 999; ++i) { // Odd number of times so that the operation doesn't cancel itself out.
    nand_and_fetch_bool((int*)&nand_and_fetch_data, (int)(long)arg);
  }
  pthread_exit(0);
}

int main() {
  pthread_t thread[NUM_THREADS];

  {
    T x = 5;
    T y = nand_and_fetch(&x, 9);
    assert(y == -2);
    assert(x == -2);
    const int oddNThreads = NUM_THREADS-1;
    for (int x = 0; x < 100; ++x) { // Test a few times for robustness, since this test is so short-lived.
      nand_and_fetch_data = 0;
      __sync_synchronize(); // This has no effect in this code, but called in here just to test that the compiler generates a valid expression for this.
      if (emscripten_has_threading_support()) {
        for (int i = 0; i < oddNThreads; ++i) pthread_create(&thread[i], NULL, thread_nand_and_fetch, (void*)-1);
        for (int i = 0; i < oddNThreads; ++i) pthread_join(thread[i], NULL);
        assert(nand_and_fetch_data == -1);
      }
    }
  }
  {
    T x = 5;
    T y = nand_and_fetch_bool(&x, 9);
    assert(y == -2);
    assert(x == -2);
    const int oddNThreads = NUM_THREADS-1;
    for (int x = 0; x < 100; ++x) { // Test a few times for robustness, since this test is so short-lived.
      nand_and_fetch_data = 0;
      if (emscripten_has_threading_support()) {
        for (int i = 0; i < oddNThreads; ++i) pthread_create(&thread[i], NULL, thread_nand_and_fetch_bool, (void*)-1);
        for (int i = 0; i < oddNThreads; ++i) pthread_join(thread[i], NULL);
        assert(nand_and_fetch_data == -1);
      }
    }
  }

  return 0;
}