1 // Copyright 2018 The Chromium Authors 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef BASE_TASK_COMMON_LAZY_NOW_H_ 6 #define BASE_TASK_COMMON_LAZY_NOW_H_ 7 8 #include "base/base_export.h" 9 #include "base/memory/raw_ptr_exclusion.h" 10 #include "base/time/time.h" 11 #include "third_party/abseil-cpp/absl/types/optional.h" 12 13 namespace base { 14 15 class TickClock; 16 17 // Now() is somewhat expensive so it makes sense not to call Now() unless we 18 // really need to and to avoid subsequent calls if already called once. 19 // LazyNow objects are expected to be short-living to represent accurate time. 20 class BASE_EXPORT LazyNow { 21 public: 22 explicit LazyNow(TimeTicks now); 23 explicit LazyNow(absl::optional<TimeTicks> now, const TickClock* tick_clock); 24 explicit LazyNow(const TickClock* tick_clock); 25 LazyNow(const LazyNow&) = delete; 26 LazyNow& operator=(const LazyNow&) = delete; 27 28 LazyNow(LazyNow&& move_from) noexcept; 29 30 // Result will not be updated on any subsesequent calls. 31 TimeTicks Now(); 32 has_value()33 bool has_value() const { return !!now_; } 34 35 private: 36 absl::optional<TimeTicks> now_; 37 // `tick_clock_` is not a raw_ptr<TickClock> as a performance optimization: 38 // The pointee doesn't need UaF protection (it has the same lifetime as the 39 // theead/sequence). 40 RAW_PTR_EXCLUSION const TickClock* tick_clock_; // Not owned. 41 }; 42 43 } // namespace base 44 45 #endif // BASE_TASK_COMMON_LAZY_NOW_H_ 46