operator.minus_equals.pass.cpp

//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
// UNSUPPORTED: c++03, c++11, c++14, c++17
// UNSUPPORTED: target={{.+}}-windows-gnu
// XFAIL: LIBCXX-AIX-FIXME
// ADDITIONAL_COMPILE_FLAGS(has-latomic): -latomic
// XFAIL: !has-64-bit-atomics
// Hangs with msan.
// UNSUPPORTED: msan

// floating-point-type operator-=(floating-point-type) volatile noexcept;
// floating-point-type operator-=(floating-point-type) noexcept;

#include <atomic>
#include <cassert>
#include <concepts>
#include <type_traits>
#include <vector>

#include "test_helper.h"
#include "test_macros.h"

#ifndef TEST_HAS_NO_THREADS
#  include "make_test_thread.h"
#  include <thread>
#endif

template <class T>
concept HasVolatileMinusEquals = requires(volatile std::atomic<T>& a, T t) { a -= t; };

template <class T, template <class> class MaybeVolatile = std::type_identity_t>
void test_impl() {
  static_assert(HasVolatileMinusEquals<T> == std::atomic<T>::is_always_lock_free);
  static_assert(noexcept(std::declval<MaybeVolatile<std::atomic<T>>&>() -= T(0)));

  // -=
  {
    MaybeVolatile<std::atomic<T>> a(3.1);
    std::same_as<T> decltype(auto) r = a -= T(1.2);
    assert(r == T(3.1) - T(1.2));
    assert(a.load() == T(3.1) - T(1.2));
  }

#ifndef TEST_HAS_NO_THREADS
  // -= concurrent
  {
    constexpr auto number_of_threads = 4;
    constexpr auto loop              = 1000;

    MaybeVolatile<std::atomic<T>> at;

    std::vector<std::thread> threads;
    threads.reserve(number_of_threads);
    for (auto i = 0; i < number_of_threads; ++i) {
      threads.push_back(support::make_test_thread([&at]() {
        for (auto j = 0; j < loop; ++j) {
          at -= T(1.234);
        }
      }));
    }

    for (auto& thread : threads) {
      thread.join();
    }

    const auto accu_neg = [](T t, int n) {
      T res(0);
      for (auto i = 0; i < n; ++i) {
        res -= t;
      }
      return res;
    };

    assert(at.load() == accu_neg(1.234, number_of_threads * loop));
  }
#endif

  // memory_order::seq_cst
  {
    auto minus_equals = [](MaybeVolatile<std::atomic<T>>& x, T old_value, T new_val) { x -= (old_value - new_val); };
    auto load         = [](MaybeVolatile<std::atomic<T>>& x) { return x.load(); };
    test_seq_cst<T, MaybeVolatile>(minus_equals, load);
  }
}

template <class T>
void test() {
  test_impl<T>();
  if constexpr (std::atomic<T>::is_always_lock_free) {
    test_impl<T, std::add_volatile_t>();
  }
}

int main(int, char**) {
  test<float>();
  test<double>();
  test<long double>();

  return 0;
}