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_TIME_TIME_OVERRIDE_H_ 6 #define BASE_TIME_TIME_OVERRIDE_H_ 7 8 #include <atomic> 9 10 #include "base/base_export.h" 11 #include "base/time/time.h" 12 #include "build/build_config.h" 13 #include "third_party/abseil-cpp/absl/types/optional.h" 14 15 namespace base { 16 17 using TimeNowFunction = decltype(&Time::Now); 18 using TimeTicksNowFunction = decltype(&TimeTicks::Now); 19 using ThreadTicksNowFunction = decltype(&ThreadTicks::Now); 20 21 // Time overrides should be used with extreme caution. Discuss with //base/time 22 // OWNERS before adding a new one. 23 namespace subtle { 24 25 // Override the return value of Time::Now and Time::NowFromSystemTime / 26 // TimeTicks::Now / ThreadTicks::Now to emulate time, e.g. for tests or to 27 // modify progression of time. It is recommended that the override be set while 28 // single-threaded and before the first call to Now() to avoid threading issues 29 // and inconsistencies in returned values. Overriding time while other threads 30 // are running is very subtle and should be reserved for developer only use 31 // cases (e.g. virtual time in devtools) where any flakiness caused by a racy 32 // time update isn't surprising. Instantiating a ScopedTimeClockOverrides while 33 // other threads are running might break their expectation that TimeTicks and 34 // ThreadTicks increase monotonically. Nested overrides are not allowed. 35 class BASE_EXPORT ScopedTimeClockOverrides { 36 public: 37 // Pass |nullptr| for any override if it shouldn't be overriden. 38 ScopedTimeClockOverrides(TimeNowFunction time_override, 39 TimeTicksNowFunction time_ticks_override, 40 ThreadTicksNowFunction thread_ticks_override); 41 42 ScopedTimeClockOverrides(const ScopedTimeClockOverrides&) = delete; 43 ScopedTimeClockOverrides& operator=(const ScopedTimeClockOverrides&) = delete; 44 45 // Restores the platform default Now() functions. 46 ~ScopedTimeClockOverrides(); 47 overrides_active()48 static bool overrides_active() { return overrides_active_; } 49 50 private: 51 static bool overrides_active_; 52 }; 53 54 // These methods return the platform default Time::Now / TimeTicks::Now / 55 // ThreadTicks::Now values even while an override is in place. These methods 56 // should only be used in places where emulated time should be disregarded. For 57 // example, they can be used to implement test timeouts for tests that may 58 // override time. 59 BASE_EXPORT Time TimeNowIgnoringOverride(); 60 BASE_EXPORT Time TimeNowFromSystemTimeIgnoringOverride(); 61 BASE_EXPORT TimeTicks TimeTicksNowIgnoringOverride(); 62 BASE_EXPORT ThreadTicks ThreadTicksNowIgnoringOverride(); 63 64 #if BUILDFLAG(IS_POSIX) 65 // Equivalent to TimeTicksNowIgnoringOverride(), but is allowed to fail and 66 // return absl::nullopt. This may safely be used in a signal handler. 67 BASE_EXPORT absl::optional<TimeTicks> MaybeTimeTicksNowIgnoringOverride(); 68 #endif 69 70 } // namespace subtle 71 72 namespace internal { 73 74 // These function pointers are used by platform-independent implementations of 75 // the Now() methods and ScopedTimeClockOverrides. They are set to point to the 76 // respective NowIgnoringOverride functions by default, but can also be set by 77 // platform-specific code to select a default implementation at runtime, thereby 78 // avoiding the indirection via the NowIgnoringOverride functions. Note that the 79 // pointers can be overridden and later reset to the NowIgnoringOverride 80 // functions by ScopedTimeClockOverrides. 81 extern std::atomic<TimeNowFunction> g_time_now_function; 82 extern std::atomic<TimeNowFunction> g_time_now_from_system_time_function; 83 extern std::atomic<TimeTicksNowFunction> g_time_ticks_now_function; 84 extern std::atomic<ThreadTicksNowFunction> g_thread_ticks_now_function; 85 86 } // namespace internal 87 88 } // namespace base 89 90 #endif // BASE_TIME_TIME_OVERRIDE_H_ 91