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// Copyright 2018 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "platform/api/time.h"
#include <chrono>
#include <ctime>
#include <ratio>
#include "util/chrono_helpers.h"
#include "util/osp_logging.h"
using std::chrono::high_resolution_clock;
using std::chrono::steady_clock;
using std::chrono::system_clock;
namespace openscreen {
Clock::time_point Clock::now() noexcept {
constexpr bool can_use_steady_clock =
std::ratio_less_equal<steady_clock::period,
Clock::kRequiredResolution>::value;
constexpr bool can_use_high_resolution_clock =
std::ratio_less_equal<high_resolution_clock::period,
Clock::kRequiredResolution>::value &&
high_resolution_clock::is_steady;
static_assert(can_use_steady_clock || can_use_high_resolution_clock,
"no suitable default clock on this platform");
// Choose whether to use the steady_clock or the high_resolution_clock. The
// general assumption here is that steady_clock will be the lesser expensive
// to use. Only fall-back to high_resolution_clock if steady_clock does not
// meet the resolution requirement.
//
// Note: Most of the expression below should be reduced at compile-time (by
// any half-decent optimizing compiler), and so there won't be any branching
// or significant math actually taking place here.
if (can_use_steady_clock) {
return Clock::time_point(
Clock::to_duration(steady_clock::now().time_since_epoch()));
}
return Clock::time_point(
Clock::to_duration(high_resolution_clock::now().time_since_epoch()));
}
std::chrono::seconds GetWallTimeSinceUnixEpoch() noexcept {
// Note: Even though std::time_t is not necessarily "seconds since UNIX epoch"
// before C++20, it is almost universally implemented that way on all
// platforms. There is a unit test to confirm this behavior, so don't worry
// about it here.
const std::time_t since_epoch = system_clock::to_time_t(system_clock::now());
// std::time_t is unspecified by the spec. If it's only a 32-bit integer, it's
// possible that values will overflow in early 2038. Warn future developers a
// year ahead of time.
if (sizeof(std::time_t) <= 4) {
constexpr std::time_t a_year_before_overflow =
std::numeric_limits<std::time_t>::max() -
to_seconds(365 * hours(24)).count();
OSP_DCHECK_LE(since_epoch, a_year_before_overflow);
}
return std::chrono::seconds(since_epoch);
}
} // namespace openscreen
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