// 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"

#ifndef _WIN32

#include <sys/types.h>

#endif

#include <algorithm>

#include <chrono>  // NOLINT(build/c++11)

#include <cstdint>

#include <cstdlib>

#include <cstring>

#include <ctime>

#include <limits>

#include "absl/base/attributes.h"

#include "absl/base/call_once.h"

#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() {

  if (!SupportsSteadyClock()) {

    return absl::GetCurrentTimeNanos();

  }

  return std::chrono::duration_cast<std::chrono::nanoseconds>(

             std::chrono::steady_clock::now().time_since_epoch())

      .count();

}

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 = RawAbsNanos();

  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 = RawAbsNanos();

  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()));

}

#ifndef _WIN32

struct timespec KernelTimeout::MakeClockAbsoluteTimespec(clockid_t c) const {

  if (!has_timeout()) {

    return absl::ToTimespec(absl::Nanoseconds(kMaxNanos));

  }

  int64_t nanos = RawAbsNanos();

  if (is_absolute_timeout()) {

    nanos -= absl::GetCurrentTimeNanos();

  } else {

    nanos -= SteadyClockNow();

  }

  struct timespec now;

  ABSL_RAW_CHECK(clock_gettime(c, &now) == 0, "clock_gettime() failed");

  absl::Duration from_clock_epoch =

      absl::DurationFromTimespec(now) + absl::Nanoseconds(nanos);

  if (from_clock_epoch <= absl::ZeroDuration()) {

    // Some callers have assumed that 0 means no timeout, so instead we return a

    // time of 1 nanosecond after the epoch. For safety we also do not return

    // negative values.

    return absl::ToTimespec(absl::Nanoseconds(1));

  }

  return absl::ToTimespec(from_clock_epoch);

}

#endif

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