base/time/README.md - chromium/src.git - Git at Google

 # //base: Time-Related Functionality

 This directory contains the portions of //base that deal with time-related
 concepts. Most critical are the classes in [time.h](time.h).
  - `Time` represents a specific wall-clock time. It is computed from the system
 clock, meaning successive requests for the current time might not always
 monotonically increase (e.g. across automatic or manual clock adjustments).
 Generally it is appropriate for anything human-visible, e.g. the last modified
 date/time of a file or a future time when Chrome will be automatically
 restarted, but users must safely handle negative durations and other effects of
 the non-monotonic clock.
  - `TimeTicks` is computed from an incrementing counter. It thus increases
 monotonically, meaning it's usually appropriate for determining how much time
 elapses between two nearby events, e.g. for function timing for profiling, or to
 schedule a task "100 milliseconds from now", regardless of what the clock reads
 at that point. However, its behavior across power-saving mode changes is
 platform-dependent, meaning it may not increment during times when the system
 clock continues to run, and the precise conditions under which it does increment
 vary by platform. This usually makes it inappropriate for long durations,
 especially in cross-platform code; for example, a histogram that uses
 `TimeTicks` to count events in a thirty-day window will show very different
 results on a platform that pauses the counter during sleep compared to one where
 it continues to run. It is also non-sensical to try and convert a `TimeTicks` to
 a `Time` and then use that as a reference point for any other `TimeTicks` value,
 since even within the same process, both intervening sleeps and intervening
 clock adjustments may mean the values should have had different reference points.
  - `TimeDelta` represents a duration between two Times or TimeTicks.

 There are also various files dealing with clocks, which are primarily useful
 when tests need to modify how the program tracks the passage of time. See
 [/base/test/task_environment.h](/base/test/task_environment.h)'s `MOCK_TIME`
 ability for
 [testing components which post tasks](/docs/threading_and_tasks_testing.md).
	# //base: Time-Related Functionality

	This directory contains the portions of //base that deal with time-related
	concepts. Most critical are the classes in [time.h](time.h).
	- `Time` represents a specific wall-clock time. It is computed from the system
	clock, meaning successive requests for the current time might not always
	monotonically increase (e.g. across automatic or manual clock adjustments).
	Generally it is appropriate for anything human-visible, e.g. the last modified
	date/time of a file or a future time when Chrome will be automatically
	restarted, but users must safely handle negative durations and other effects of
	the non-monotonic clock.
	- `TimeTicks` is computed from an incrementing counter. It thus increases
	monotonically, meaning it's usually appropriate for determining how much time
	elapses between two nearby events, e.g. for function timing for profiling, or to
	schedule a task "100 milliseconds from now", regardless of what the clock reads
	at that point. However, its behavior across power-saving mode changes is
	platform-dependent, meaning it may not increment during times when the system
	clock continues to run, and the precise conditions under which it does increment
	vary by platform. This usually makes it inappropriate for long durations,
	especially in cross-platform code; for example, a histogram that uses
	`TimeTicks` to count events in a thirty-day window will show very different
	results on a platform that pauses the counter during sleep compared to one where
	it continues to run. It is also non-sensical to try and convert a `TimeTicks` to
	a `Time` and then use that as a reference point for any other `TimeTicks` value,
	since even within the same process, both intervening sleeps and intervening
	clock adjustments may mean the values should have had different reference points.
	- `TimeDelta` represents a duration between two Times or TimeTicks.

	There are also various files dealing with clocks, which are primarily useful
	when tests need to modify how the program tracks the passage of time. See
	[/base/test/task_environment.h](/base/test/task_environment.h)'s `MOCK_TIME`
	ability for
	[testing components which post tasks](/docs/threading_and_tasks_testing.md).