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TMessagesProj/jni/voip/webrtc/absl/synchronization/internal/kernel_timeout.h

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+// Copyright 2017 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.
+
+#ifndef ABSL_SYNCHRONIZATION_INTERNAL_KERNEL_TIMEOUT_H_
+#define ABSL_SYNCHRONIZATION_INTERNAL_KERNEL_TIMEOUT_H_
+
+#ifndef _WIN32
+#include <sys/types.h>
+#endif
+
+#include <algorithm>
+#include <chrono>  // NOLINT(build/c++11)
+#include <cstdint>
+#include <ctime>
+#include <limits>
+
+#include "absl/base/config.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/time/clock.h"
+#include "absl/time/time.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace synchronization_internal {
+
+// An optional timeout, with nanosecond granularity.
+//
+// This is a private low-level API for use by a handful of low-level
+// components. Higher-level components should build APIs based on
+// absl::Time and absl::Duration.
+class KernelTimeout {
+ public:
+  // Construct an absolute timeout that should expire at `t`.
+  explicit KernelTimeout(absl::Time t);
+
+  // Construct a relative timeout that should expire after `d`.
+  explicit KernelTimeout(absl::Duration d);
+
+  // Infinite timeout.
+  constexpr KernelTimeout() : rep_(kNoTimeout) {}
+
+  // A more explicit factory for those who prefer it.
+  // Equivalent to `KernelTimeout()`.
+  static constexpr KernelTimeout Never() { return KernelTimeout(); }
+
+  // Returns true if there is a timeout that will eventually expire.
+  // Returns false if the timeout is infinite.
+  bool has_timeout() const { return rep_ != kNoTimeout; }
+
+  // If `has_timeout()` is true, returns true if the timeout was provided as an
+  // `absl::Time`. The return value is undefined if `has_timeout()` is false
+  // because all indefinite timeouts are equivalent.
+  bool is_absolute_timeout() const { return (rep_ & 1) == 0; }
+
+  // If `has_timeout()` is true, returns true if the timeout was provided as an
+  // `absl::Duration`. The return value is undefined if `has_timeout()` is false
+  // because all indefinite timeouts are equivalent.
+  bool is_relative_timeout() const { return (rep_ & 1) == 1; }
+
+  // Convert to `struct timespec` for interfaces that expect an absolute
+  // timeout. If !has_timeout() or is_relative_timeout(), attempts to convert to
+  // a reasonable absolute timeout, but callers should to test has_timeout() and
+  // is_relative_timeout() and prefer to use a more appropriate interface.
+  struct timespec MakeAbsTimespec() const;
+
+  // Convert to `struct timespec` for interfaces that expect a relative
+  // timeout. If !has_timeout() or is_absolute_timeout(), attempts to convert to
+  // a reasonable relative timeout, but callers should to test has_timeout() and
+  // is_absolute_timeout() and prefer to use a more appropriate interface. Since
+  // the return value is a relative duration, it should be recomputed by calling
+  // this method in the case of a spurious wakeup.
+  struct timespec MakeRelativeTimespec() const;
+
+#ifndef _WIN32
+  // Convert to `struct timespec` for interfaces that expect an absolute timeout
+  // on a specific clock `c`. This is similar to `MakeAbsTimespec()`, but
+  // callers usually want to use this method with `CLOCK_MONOTONIC` when
+  // relative timeouts are requested, and when the appropriate interface expects
+  // an absolute timeout relative to a specific clock (for example,
+  // pthread_cond_clockwait() or sem_clockwait()). If !has_timeout(), attempts
+  // to convert to a reasonable absolute timeout, but callers should to test
+  // has_timeout() prefer to use a more appropriate interface.
+  struct timespec MakeClockAbsoluteTimespec(clockid_t c) const;
+#endif
+
+  // Convert to unix epoch nanos for interfaces that expect an absolute timeout
+  // in nanoseconds. If !has_timeout() or is_relative_timeout(), attempts to
+  // convert to a reasonable absolute timeout, but callers should to test
+  // has_timeout() and is_relative_timeout() and prefer to use a more
+  // appropriate interface.
+  int64_t MakeAbsNanos() const;
+
+  // Converts to milliseconds from now, or INFINITE when
+  // !has_timeout(). For use by SleepConditionVariableSRW on
+  // Windows. Callers should recognize that the return value is a
+  // relative duration (it should be recomputed by calling this method
+  // in the case of a spurious wakeup).
+  // This header file may be included transitively by public header files,
+  // so we define our own DWORD and INFINITE instead of getting them from
+  // <intsafe.h> and <WinBase.h>.
+  typedef unsigned long DWord;  // NOLINT
+  DWord InMillisecondsFromNow() const;
+
+  // Convert to std::chrono::time_point for interfaces that expect an absolute
+  // timeout, like std::condition_variable::wait_until(). If !has_timeout() or
+  // is_relative_timeout(), attempts to convert to a reasonable absolute
+  // timeout, but callers should test has_timeout() and is_relative_timeout()
+  // and prefer to use a more appropriate interface.
+  std::chrono::time_point<std::chrono::system_clock> ToChronoTimePoint() const;
+
+  // Convert to std::chrono::time_point for interfaces that expect a relative
+  // timeout, like std::condition_variable::wait_for(). If !has_timeout() or
+  // is_absolute_timeout(), attempts to convert to a reasonable relative
+  // timeout, but callers should test has_timeout() and is_absolute_timeout()
+  // and prefer to use a more appropriate interface. Since the return value is a
+  // relative duration, it should be recomputed by calling this method in the
+  // case of a spurious wakeup.
+  std::chrono::nanoseconds ToChronoDuration() const;
+
+  // Returns true if steady (aka monotonic) clocks are supported by the system.
+  // This method exists because go/btm requires synchronized clocks, and
+  // thus requires we use the system (aka walltime) clock.
+  static constexpr bool SupportsSteadyClock() { return true; }
+
+ private:
+  // Returns the current time, expressed as a count of nanoseconds since the
+  // epoch used by an arbitrary clock. The implementation tries to use a steady
+  // (monotonic) clock if one is available.
+  static int64_t SteadyClockNow();
+
+  // Internal representation.
+  //   - If the value is kNoTimeout, then the timeout is infinite, and
+  //     has_timeout() will return true.
+  //   - If the low bit is 0, then the high 63 bits is the number of nanoseconds
+  //     after the unix epoch.
+  //   - If the low bit is 1, then the high 63 bits is the number of nanoseconds
+  //     after the epoch used by SteadyClockNow().
+  //
+  // In all cases the time is stored as an absolute time, the only difference is
+  // the clock epoch. The use of absolute times is important since in the case
+  // of a relative timeout with a spurious wakeup, the program would have to
+  // restart the wait, and thus needs a way of recomputing the remaining time.
+  uint64_t rep_;
+
+  // Returns the number of nanoseconds stored in the internal representation.
+  // When combined with the clock epoch indicated by the low bit (which is
+  // accessed through is_absolute_timeout() and is_relative_timeout()), the
+  // return value is used to compute when the timeout should occur.
+  int64_t RawAbsNanos() const { return static_cast<int64_t>(rep_ >> 1); }
+
+  // Converts to nanoseconds from now. Since the return value is a relative
+  // duration, it should be recomputed by calling this method in the case of a
+  // spurious wakeup.
+  int64_t InNanosecondsFromNow() const;
+
+  // A value that represents no timeout (or an infinite timeout).
+  static constexpr uint64_t kNoTimeout = (std::numeric_limits<uint64_t>::max)();
+
+  // The maximum value that can be stored in the high 63 bits.
+  static constexpr int64_t kMaxNanos = (std::numeric_limits<int64_t>::max)();
+};
+
+}  // namespace synchronization_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_SYNCHRONIZATION_INTERNAL_KERNEL_TIMEOUT_H_