clocks

README

go-clocks provides a modern context-aware clock interface

When writing code that involves time, it is not uncommon to want control over the flow of that resource (particularly for tests). Many applications end up storing a field called now and of type func() time.Time, to mock out time.Now(), but that only covers a fraction of the time package's interface, and only covers the most trivial cases.

The Clock interface in go-clocks covers both querying and waiting for time. Querying is handled via Clock.Now() and Clock.Until() while waiting is handled by Clock.SleepFor() and Clock.SleepUntil().

Using Clock

Generally, it is recommended store a field of type Clock in struct-types that might need to interact with time. In production, one should use DefaultClock(), while in tests, one will generally want some combination of fake.Clock and offset.Clock.

fake.Clock and tests

While Clock is a nice interface with both context-aware Clock.SleepFor() and Clock.SleepUntil(), it really shines when combined with the fake.Clock in this repository's fake subpackage.

fake.Clock has a number of methods for doing implicit synchronization based on the number of instances of SleepFor/SleepUntil waiting on a particular fake.Clock instance.

offset.Clock and tests

A significantly simpler Clock implementation lives in the offset subpackage in the form of the offset.Clock type, which adds a constant offset to a wrapped Clock. This is useful for simulating clock-skew between different components within a test without having to do extra bookkeeping associated with multiple fake.Clocks.

Dependencies

go-clocks very deliberately has zero dependencies aside from the Go standard library.

Test coverage

As of the v1.0.0 release of go-clocks, the package has 100% test statement-based coverage as measured by go test -cover in all three packages. We endeavor to keep it that way.

Documentation

Overview

Package clocks provides the Clock interface and a default implementations: the defaultClock implementation (returned by DefaultClock())

defaultClock should always be used within production, as it is a trivial wrapper around the real clock-derived functions in the time package of the Go standard library.

In the fake subpackage there is a fake.Clock (created by fake.NewClock()) fake.Clock is present for use in tests, with some helpers for useful synchronization, such as AwaitSleepers() which lets a test goroutine block until some number of other goroutines are sleeping. See the documentation on the individual methods of fake.Clock for more specific documentation.

The offset subpackage contains an offset.Clock type which simply adds a constant offset to any interactions with an absolute time. This type is most useful for simulating clock-skew/unsynchronization in combination with the fake-clock.

Index

• type Clock
  • func DefaultClock() Clock
• type StopTimer
• type Timer

Types

type Clock

type Clock interface {
	Now() time.Time
	Until(time.Time) time.Duration
	// SleepUntil blocks until either ctx expires or until arrives.
	// Return value is false if context-cancellation/expiry prompted an
	// early return.
	SleepUntil(ctx context.Context, until time.Time) bool
	// SleepFor is the relative-time equivalent of SleepUntil. In the
	// default implementation, this is the lower-level method, but other
	// implementations may disagree.
	SleepFor(ctx context.Context, dur time.Duration) bool

	// AfterFunc is a time-relative primitive, equivalent to time.AfterFunc.
	// (in the default clock, it *is* delegated directly to time.AfterFunc)
	// The callback function f will be executed after the interval d has
	// elapsed, unless the returned timer's Stop() method is called first.
	AfterFunc(d time.Duration, f func()) StopTimer

	// ContextWithDeadline behaves like context.WithDeadline, but it uses the
	// clock to determine the when the deadline has expired.
	ContextWithDeadline(ctx context.Context, t time.Time) (context.Context, context.CancelFunc)
	// ContextWithDeadlineCause behaves like context.WithDeadlineCause, but it
	// uses the clock to determine the when the deadline has expired. Cause is
	// ignored in Go 1.20 and earlier.
	ContextWithDeadlineCause(ctx context.Context, t time.Time, cause error) (context.Context, context.CancelFunc)
	// ContextWithTimeout behaves like context.WithTimeout, but it uses the
	// clock to determine the when the timeout has elapsed.
	ContextWithTimeout(ctx context.Context, d time.Duration) (context.Context, context.CancelFunc)
	// ContextWithTimeoutCause behaves like context.WithTimeoutCause, but it
	// uses the clock to determine the when the timeout has elapsed. Cause is
	// ignored in Go 1.20 and earlier.
	ContextWithTimeoutCause(ctx context.Context, d time.Duration, cause error) (context.Context, context.CancelFunc)

	// NewTimer returns a Timer implementation which will fire after at
	// least the specified duration [d]. The Ch() method returns a channel,
	// and should be called inline with the receive or select case.
	//
	// Timers are most useful in select/case blocks. For simple cases,
	// SleepFor should be preferred.
	//
	// Stop() is inherently racy. Be wary of the return value.
	NewTimer(d time.Duration) Timer
}

Clock is generally only used for testing, but could be used for userspace clock-synchronization as well.

func DefaultClock

func DefaultClock() Clock

DefaultClock returns a clock that minimally wraps the `time` package

type StopTimer

type StopTimer interface {
	// Stop attempts to prevent a timer from firing, returning true if it
	// succeeds in preventing the timer from firing, and false if it
	// already fired.
	Stop() bool
}

StopTimer exposes a `Stop()` method for an equivalent object to time.Timer (in the defaultClock case, it may be an actual time.Timer).

type Timer

type Timer interface {
	StopTimer
	// Ch returns the channel for the timer
	// For the fake clock's tracking to work, one must always dereference
	// the channel returned by this method directly, as it relies on a
	// finalizer to figure out when a listening goroutine woke up.
	Ch() *<-chan time.Time
}

Timer exposes methods for an equivalent object to time.Timer (in the defaultClock case, it may be an actual time.Timer)