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// Copyright 2023 The Abseil Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "absl/synchronization/internal/kernel_timeout.h"
#include <algorithm>
#include <chrono> // NOLINT(build/c++11)
#include <cstdint>
#include <ctime>
#include <limits>
#include "absl/base/config.h"
#include "absl/time/time.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace synchronization_internal {
#ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
constexpr uint64_t KernelTimeout::kNoTimeout;
constexpr int64_t KernelTimeout::kMaxNanos;
#endif
int64_t KernelTimeout::SteadyClockNow() {
#ifdef __GOOGLE_GRTE_VERSION__
// go/btm requires synchronized clocks, so we have to use the system
// clock.
return absl::GetCurrentTimeNanos();
#else
return std::chrono::duration_cast<std::chrono::nanoseconds>(
std::chrono::steady_clock::now().time_since_epoch())
.count();
#endif
}
KernelTimeout::KernelTimeout(absl::Time t) {
// `absl::InfiniteFuture()` is a common "no timeout" value and cheaper to
// compare than convert.
if (t == absl::InfiniteFuture()) {
rep_ = kNoTimeout;
return;
}
int64_t unix_nanos = absl::ToUnixNanos(t);
// A timeout that lands before the unix epoch is converted to 0.
// In theory implementations should expire these timeouts immediately.
if (unix_nanos < 0) {
unix_nanos = 0;
}
// Values greater than or equal to kMaxNanos are converted to infinite.
if (unix_nanos >= kMaxNanos) {
rep_ = kNoTimeout;
return;
}
rep_ = static_cast<uint64_t>(unix_nanos) << 1;
}
KernelTimeout::KernelTimeout(absl::Duration d) {
// `absl::InfiniteDuration()` is a common "no timeout" value and cheaper to
// compare than convert.
if (d == absl::InfiniteDuration()) {
rep_ = kNoTimeout;
return;
}
int64_t nanos = absl::ToInt64Nanoseconds(d);
// Negative durations are normalized to 0.
// In theory implementations should expire these timeouts immediately.
if (nanos < 0) {
nanos = 0;
}
int64_t now = SteadyClockNow();
if (nanos > kMaxNanos - now) {
// Durations that would be greater than kMaxNanos are converted to infinite.
rep_ = kNoTimeout;
return;
}
nanos += now;
rep_ = (static_cast<uint64_t>(nanos) << 1) | uint64_t{1};
}
int64_t KernelTimeout::MakeAbsNanos() const {
if (!has_timeout()) {
return kMaxNanos;
}
int64_t nanos = RawNanos();
if (is_relative_timeout()) {
// We need to change epochs, because the relative timeout might be
// represented by an absolute timestamp from another clock.
nanos = std::max<int64_t>(nanos - SteadyClockNow(), 0);
int64_t now = absl::GetCurrentTimeNanos();
if (nanos > kMaxNanos - now) {
// Overflow.
nanos = kMaxNanos;
} else {
nanos += now;
}
} else if (nanos == 0) {
// Some callers have assumed that 0 means no timeout, so instead we return a
// time of 1 nanosecond after the epoch.
nanos = 1;
}
return nanos;
}
int64_t KernelTimeout::InNanosecondsFromNow() const {
if (!has_timeout()) {
return kMaxNanos;
}
int64_t nanos = RawNanos();
if (is_absolute_timeout()) {
return std::max<int64_t>(nanos - absl::GetCurrentTimeNanos(), 0);
}
return std::max<int64_t>(nanos - SteadyClockNow(), 0);
}
struct timespec KernelTimeout::MakeAbsTimespec() const {
return absl::ToTimespec(absl::Nanoseconds(MakeAbsNanos()));
}
struct timespec KernelTimeout::MakeRelativeTimespec() const {
return absl::ToTimespec(absl::Nanoseconds(InNanosecondsFromNow()));
}
KernelTimeout::DWord KernelTimeout::InMillisecondsFromNow() const {
constexpr DWord kInfinite = std::numeric_limits<DWord>::max();
if (!has_timeout()) {
return kInfinite;
}
constexpr uint64_t kNanosInMillis = uint64_t{1'000'000};
constexpr uint64_t kMaxValueNanos =
std::numeric_limits<int64_t>::max() - kNanosInMillis + 1;
uint64_t ns_from_now = static_cast<uint64_t>(InNanosecondsFromNow());
if (ns_from_now >= kMaxValueNanos) {
// Rounding up would overflow.
return kInfinite;
}
// Convert to milliseconds, always rounding up.
uint64_t ms_from_now = (ns_from_now + kNanosInMillis - 1) / kNanosInMillis;
if (ms_from_now > kInfinite) {
return kInfinite;
}
return static_cast<DWord>(ms_from_now);
}
std::chrono::time_point<std::chrono::system_clock>
KernelTimeout::ToChronoTimePoint() const {
if (!has_timeout()) {
return std::chrono::time_point<std::chrono::system_clock>::max();
}
// The cast to std::microseconds is because (on some platforms) the
// std::ratio used by std::chrono::steady_clock doesn't convert to
// std::nanoseconds, so it doesn't compile.
auto micros = std::chrono::duration_cast<std::chrono::microseconds>(
std::chrono::nanoseconds(MakeAbsNanos()));
return std::chrono::system_clock::from_time_t(0) + micros;
}
std::chrono::nanoseconds KernelTimeout::ToChronoDuration() const {
if (!has_timeout()) {
return std::chrono::nanoseconds::max();
}
return std::chrono::nanoseconds(InNanosecondsFromNow());
}
} // namespace synchronization_internal
ABSL_NAMESPACE_END
} // namespace absl
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