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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.
+//
+
+// An optional absolute timeout, with nanosecond granularity,
+// compatible with absl::Time. Suitable for in-register
+// parameter-passing (e.g. syscalls.)
+// Constructible from a absl::Time (for a timeout to be respected) or {}
+// (for "no timeout".)
+// This is a private low-level API for use by a handful of low-level
+// components that are friends of this class. Higher-level components
+// should build APIs based on absl::Time and absl::Duration.
+
+#ifndef ABSL_SYNCHRONIZATION_INTERNAL_KERNEL_TIMEOUT_H_
+#define ABSL_SYNCHRONIZATION_INTERNAL_KERNEL_TIMEOUT_H_
+
+#include <time.h>
+#include <algorithm>
+#include <limits>
+
+#include "absl/base/internal/raw_logging.h"
+#include "absl/time/clock.h"
+#include "absl/time/time.h"
+
+namespace absl {
+namespace synchronization_internal {
+
+class Futex;
+class Waiter;
+
+class KernelTimeout {
+ public:
+ // A timeout that should expire at <t>. Any value, in the full
+ // InfinitePast() to InfiniteFuture() range, is valid here and will be
+ // respected.
+ explicit KernelTimeout(absl::Time t) : ns_(MakeNs(t)) {}
+ // No timeout.
+ KernelTimeout() : ns_(0) {}
+
+ // A more explicit factory for those who prefer it. Equivalent to {}.
+ static KernelTimeout Never() { return {}; }
+
+ // We explicitly do not support other custom formats: timespec, int64_t nanos.
+ // Unify on this and absl::Time, please.
+
+ bool has_timeout() const { return ns_ != 0; }
+
+ private:
+ // internal rep, not user visible: ns after unix epoch.
+ // zero = no timeout.
+ // Negative we treat as an unlikely (and certainly expired!) but valid
+ // timeout.
+ int64_t ns_;
+
+ static int64_t MakeNs(absl::Time t) {
+ // optimization--InfiniteFuture is common "no timeout" value
+ // and cheaper to compare than convert.
+ if (t == absl::InfiniteFuture()) return 0;
+ int64_t x = ToUnixNanos(t);
+
+ // A timeout that lands exactly on the epoch (x=0) needs to be respected,
+ // so we alter it unnoticably to 1. Negative timeouts are in
+ // theory supported, but handled poorly by the kernel (long
+ // delays) so push them forward too; since all such times have
+ // already passed, it's indistinguishable.
+ if (x <= 0) x = 1;
+ // A time larger than what can be represented to the kernel is treated
+ // as no timeout.
+ if (x == (std::numeric_limits<int64_t>::max)()) x = 0;
+ return x;
+ }
+
+ // Convert to parameter for sem_timedwait/futex/similar. Only for approved
+ // users. Do not call if !has_timeout.
+ struct timespec MakeAbsTimespec() {
+ int64_t n = ns_;
+ static const int64_t kNanosPerSecond = 1000 * 1000 * 1000;
+ if (n == 0) {
+ ABSL_RAW_LOG(
+ ERROR,
+ "Tried to create a timespec from a non-timeout; never do this.");
+ // But we'll try to continue sanely. no-timeout ~= saturated timeout.
+ n = (std::numeric_limits<int64_t>::max)();
+ }
+
+ // Kernel APIs validate timespecs as being at or after the epoch,
+ // despite the kernel time type being signed. However, no one can
+ // tell the difference between a timeout at or before the epoch (since
+ // all such timeouts have expired!)
+ if (n < 0) n = 0;
+
+ struct timespec abstime;
+ int64_t seconds = (std::min)(n / kNanosPerSecond,
+ int64_t{(std::numeric_limits<time_t>::max)()});
+ abstime.tv_sec = static_cast<time_t>(seconds);
+ abstime.tv_nsec =
+ static_cast<decltype(abstime.tv_nsec)>(n % kNanosPerSecond);
+ return abstime;
+ }
+
+#ifdef _WIN32
+ // 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 {
+ constexpr DWord kInfinite = (std::numeric_limits<DWord>::max)();
+ if (!has_timeout()) {
+ return kInfinite;
+ }
+ // The use of absl::Now() to convert from absolute time to
+ // relative time means that absl::Now() cannot use anything that
+ // depends on KernelTimeout (for example, Mutex) on Windows.
+ int64_t now = ToUnixNanos(absl::Now());
+ if (ns_ >= now) {
+ // Round up so that Now() + ms_from_now >= ns_.
+ constexpr uint64_t max_nanos =
+ (std::numeric_limits<int64_t>::max)() - 999999u;
+ uint64_t ms_from_now =
+ (std::min<uint64_t>(max_nanos, ns_ - now) + 999999u) / 1000000u;
+ if (ms_from_now > kInfinite) {
+ return kInfinite;
+ }
+ return static_cast<DWord>(ms_from_now);
+ }
+ return 0;
+ }
+#endif
+
+ friend class Futex;
+ friend class Waiter;
+};
+
+} // namespace synchronization_internal
+} // namespace absl
+
+#endif // ABSL_SYNCHRONIZATION_INTERNAL_KERNEL_TIMEOUT_H_
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