1 files changed, 225 insertions, 0 deletions
diff --git a/absl/synchronization/internal/kernel_timeout.cc b/absl/synchronization/internal/kernel_timeout.cc
new file mode 100644
index 00000000..48ea6287
--- /dev/null
+++ b/absl/synchronization/internal/kernel_timeout.cc
@@ -0,0 +1,225 @@
+// 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