082c006c04
... notably, this includes Abseil's own StatusOr type, which conflicted with our implementation (that was taken from TensorFlow). Change-Id: Ie7d6764b64055caaeb8dc7b6b9d066291e6b538f
124 lines
4.4 KiB
C++
124 lines
4.4 KiB
C++
// Copyright 2017 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// UnscaledCycleClock
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// An UnscaledCycleClock yields the value and frequency of a cycle counter
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// that increments at a rate that is approximately constant.
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// This class is for internal use only, you should consider using CycleClock
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// instead.
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//
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// Notes:
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// The cycle counter frequency is not necessarily the core clock frequency.
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// That is, CycleCounter cycles are not necessarily "CPU cycles".
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//
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// An arbitrary offset may have been added to the counter at power on.
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//
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// On some platforms, the rate and offset of the counter may differ
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// slightly when read from different CPUs of a multiprocessor. Usually,
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// we try to ensure that the operating system adjusts values periodically
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// so that values agree approximately. If you need stronger guarantees,
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// consider using alternate interfaces.
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//
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// The CPU is not required to maintain the ordering of a cycle counter read
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// with respect to surrounding instructions.
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#ifndef ABSL_BASE_INTERNAL_UNSCALEDCYCLECLOCK_H_
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#define ABSL_BASE_INTERNAL_UNSCALEDCYCLECLOCK_H_
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#include <cstdint>
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#if defined(__APPLE__)
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#include <TargetConditionals.h>
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#endif
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#include "absl/base/port.h"
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// The following platforms have an implementation of a hardware counter.
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#if defined(__i386__) || defined(__x86_64__) || defined(__aarch64__) || \
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defined(__powerpc__) || defined(__ppc__) || \
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defined(_M_IX86) || defined(_M_X64)
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#define ABSL_HAVE_UNSCALED_CYCLECLOCK_IMPLEMENTATION 1
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#else
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#define ABSL_HAVE_UNSCALED_CYCLECLOCK_IMPLEMENTATION 0
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#endif
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// The following platforms often disable access to the hardware
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// counter (through a sandbox) even if the underlying hardware has a
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// usable counter. The CycleTimer interface also requires a *scaled*
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// CycleClock that runs at atleast 1 MHz. We've found some Android
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// ARM64 devices where this is not the case, so we disable it by
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// default on Android ARM64.
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#if defined(__native_client__) || \
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(defined(TARGET_OS_IPHONE) && TARGET_OS_IPHONE) || \
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(defined(__ANDROID__) && defined(__aarch64__))
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#define ABSL_USE_UNSCALED_CYCLECLOCK_DEFAULT 0
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#else
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#define ABSL_USE_UNSCALED_CYCLECLOCK_DEFAULT 1
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#endif
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// UnscaledCycleClock is an optional internal feature.
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// Use "#if ABSL_USE_UNSCALED_CYCLECLOCK" to test for its presence.
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// Can be overridden at compile-time via -DABSL_USE_UNSCALED_CYCLECLOCK=0|1
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#if !defined(ABSL_USE_UNSCALED_CYCLECLOCK)
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#define ABSL_USE_UNSCALED_CYCLECLOCK \
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(ABSL_HAVE_UNSCALED_CYCLECLOCK_IMPLEMENTATION && \
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ABSL_USE_UNSCALED_CYCLECLOCK_DEFAULT)
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#endif
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#if ABSL_USE_UNSCALED_CYCLECLOCK
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// This macro can be used to test if UnscaledCycleClock::Frequency()
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// is NominalCPUFrequency() on a particular platform.
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#if (defined(__i386__) || defined(__x86_64__) || \
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defined(_M_IX86) || defined(_M_X64))
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#define ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY
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#endif
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace time_internal {
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class UnscaledCycleClockWrapperForGetCurrentTime;
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} // namespace time_internal
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namespace base_internal {
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class CycleClock;
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class UnscaledCycleClockWrapperForInitializeFrequency;
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class UnscaledCycleClock {
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private:
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UnscaledCycleClock() = delete;
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// Return the value of a cycle counter that counts at a rate that is
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// approximately constant.
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static int64_t Now();
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// Return the how much UnscaledCycleClock::Now() increases per second.
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// This is not necessarily the core CPU clock frequency.
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// It may be the nominal value report by the kernel, rather than a measured
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// value.
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static double Frequency();
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// Allowed users
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friend class base_internal::CycleClock;
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friend class time_internal::UnscaledCycleClockWrapperForGetCurrentTime;
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friend class base_internal::UnscaledCycleClockWrapperForInitializeFrequency;
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};
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} // namespace base_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_USE_UNSCALED_CYCLECLOCK
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#endif // ABSL_BASE_INTERNAL_UNSCALEDCYCLECLOCK_H_
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