diff options
Diffstat (limited to 'absl/base/internal/cycleclock.cc')
-rw-r--r-- | absl/base/internal/cycleclock.cc | 32 |
1 files changed, 28 insertions, 4 deletions
diff --git a/absl/base/internal/cycleclock.cc b/absl/base/internal/cycleclock.cc index d99b63d3..9868e549 100644 --- a/absl/base/internal/cycleclock.cc +++ b/absl/base/internal/cycleclock.cc @@ -4,7 +4,7 @@ // you may not use this file except in compliance with the License. // You may obtain a copy of the License at // -// http://www.apache.org/licenses/LICENSE-2.0 +// 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, @@ -22,12 +22,13 @@ #include "absl/base/internal/cycleclock.h" +#include <atomic> #include <chrono> // NOLINT(build/c++11) #include "absl/base/internal/unscaledcycleclock.h" namespace absl { -inline namespace lts_2018_12_18 { +inline namespace lts_2019_08_08 { namespace base_internal { #if ABSL_USE_UNSCALED_CYCLECLOCK @@ -53,17 +54,40 @@ static constexpr int32_t kShift = 2; #endif static constexpr double kFrequencyScale = 1.0 / (1 << kShift); +static std::atomic<CycleClockSourceFunc> cycle_clock_source; + +CycleClockSourceFunc LoadCycleClockSource() { + // Optimize for the common case (no callback) by first doing a relaxed load; + // this is significantly faster on non-x86 platforms. + if (cycle_clock_source.load(std::memory_order_relaxed) == nullptr) { + return nullptr; + } + // This corresponds to the store(std::memory_order_release) in + // CycleClockSource::Register, and makes sure that any updates made prior to + // registering the callback are visible to this thread before the callback is + // invoked. + return cycle_clock_source.load(std::memory_order_acquire); +} } // namespace int64_t CycleClock::Now() { - return base_internal::UnscaledCycleClock::Now() >> kShift; + auto fn = LoadCycleClockSource(); + if (fn == nullptr) { + return base_internal::UnscaledCycleClock::Now() >> kShift; + } + return fn() >> kShift; } double CycleClock::Frequency() { return kFrequencyScale * base_internal::UnscaledCycleClock::Frequency(); } +void CycleClockSource::Register(CycleClockSourceFunc source) { + // Corresponds to the load(std::memory_order_acquire) in LoadCycleClockSource. + cycle_clock_source.store(source, std::memory_order_release); +} + #else int64_t CycleClock::Now() { @@ -79,5 +103,5 @@ double CycleClock::Frequency() { #endif } // namespace base_internal -} // inline namespace lts_2018_12_18 +} // inline namespace lts_2019_08_08 } // namespace absl |