wait

Documentation

Overview

Package wait provides tools for polling or listening for changes to a condition.

Index

• Variables
• func ExponentialBackoff(backoff Backoff, condition ConditionFunc) error
• func Forever(f func(), period time.Duration)
• func Jitter(duration time.Duration, maxFactor float64) time.Duration
• func JitterUntil(f func(), period time.Duration, jitterFactor float64, sliding bool, ...)
• func NonSlidingUntil(f func(), period time.Duration, stopCh <-chan struct{})
• func Poll(interval, timeout time.Duration, condition ConditionFunc) error
• func PollImmediate(interval, timeout time.Duration, condition ConditionFunc) error
• func PollImmediateInfinite(interval time.Duration, condition ConditionFunc) error
• func PollInfinite(interval time.Duration, condition ConditionFunc) error
• func PollUntil(interval time.Duration, condition ConditionFunc, stopCh <-chan struct{}) error
• func Until(f func(), period time.Duration, stopCh <-chan struct{})
• func WaitFor(wait WaitFunc, fn ConditionFunc, done <-chan struct{}) error
• type Backoff
• type ConditionFunc
• type WaitFunc

Variables

var ErrWaitTimeout = errors.New("timed out waiting for the condition")

ErrWaitTimeout is returned when the condition exited without success.

var ForeverTestTimeout = time.Second * 30

For any test of the style:

...
<- time.After(timeout):
   t.Errorf("Timed out")

The value for timeout should effectively be "forever." Obviously we don't want our tests to truly lock up forever, but 30s is long enough that it is effectively forever for the things that can slow down a run on a heavily contended machine (GC, seeks, etc), but not so long as to make a developer ctrl-c a test run if they do happen to break that test.

var NeverStop <-chan struct{} = make(chan struct{})

NeverStop may be passed to Until to make it never stop.

Functions

func ExponentialBackoff

func ExponentialBackoff(backoff Backoff, condition ConditionFunc) error

ExponentialBackoff repeats a condition check with exponential backoff.

It checks the condition up to Steps times, increasing the wait by multipling the previous duration by Factor.

If Jitter is greater than zero, a random amount of each duration is added (between duration and duration*(1+jitter)).

If the condition never returns true, ErrWaitTimeout is returned. All other errors terminate immediately.

func Forever

func Forever(f func(), period time.Duration)

Forever calls f every period for ever.

Forever is syntactic sugar on top of Until.

func Jitter

func Jitter(duration time.Duration, maxFactor float64) time.Duration

Jitter returns a time.Duration between duration and duration + maxFactor * duration.

This allows clients to avoid converging on periodic behavior. If maxFactor is 0.0, a suggested default value will be chosen.

func JitterUntil

func JitterUntil(f func(), period time.Duration, jitterFactor float64, sliding bool, stopCh <-chan struct{})

JitterUntil loops until stop channel is closed, running f every period.

If jitterFactor is positive, the period is jittered before every run of f. If jitterFactor is not positive, the period is unchanged and not jitterd.

If slidingis true, the period is computed after f runs. If it is false then period includes the runtime for f.

Close stopCh to stop. f may not be invoked if stop channel is already closed. Pass NeverStop to if you don't want it stop.

func NonSlidingUntil

func NonSlidingUntil(f func(), period time.Duration, stopCh <-chan struct{})

NonSlidingUntil loops until stop channel is closed, running f every period.

NonSlidingUntil is syntactic sugar on top of JitterUntil with zero jitter factor, with sliding = false (meaning the timer for period starts at the same time as the function starts).

func Poll

func Poll(interval, timeout time.Duration, condition ConditionFunc) error

Poll tries a condition func until it returns true, an error, or the timeout is reached.

Poll always waits the interval before the run of 'condition'. 'condition' will always be invoked at least once.

Some intervals may be missed if the condition takes too long or the time window is too short.

If you want to Poll something forever, see PollInfinite.

func PollImmediate

func PollImmediate(interval, timeout time.Duration, condition ConditionFunc) error

PollImmediate tries a condition func until it returns true, an error, or the timeout is reached.

Poll always checks 'condition' before waiting for the interval. 'condition' will always be invoked at least once.

Some intervals may be missed if the condition takes too long or the time window is too short.

If you want to Poll something forever, see PollInfinite.

func PollImmediateInfinite

func PollImmediateInfinite(interval time.Duration, condition ConditionFunc) error

PollImmediateInfinite tries a condition func until it returns true or an error

PollImmediateInfinite runs the 'condition' before waiting for the interval.

Some intervals may be missed if the condition takes too long or the time window is too short.

func PollInfinite

func PollInfinite(interval time.Duration, condition ConditionFunc) error

PollInfinite tries a condition func until it returns true or an error

PollInfinite always waits the interval before the run of 'condition'.

Some intervals may be missed if the condition takes too long or the time window is too short.

func PollUntil

func PollUntil(interval time.Duration, condition ConditionFunc, stopCh <-chan struct{}) error

PollUntil tries a condition func until it returns true, an error or stopCh is closed.

PolUntil always waits interval before the first run of 'condition'. 'condition' will always be invoked at least once.

func Until

func Until(f func(), period time.Duration, stopCh <-chan struct{})

Until loops until stop channel is closed, running f every period.

Until is syntactic sugar on top of JitterUntil with zero jitter factor and with sliding = true (which means the timer for period starts after the f completes).

func WaitFor

func WaitFor(wait WaitFunc, fn ConditionFunc, done <-chan struct{}) error

WaitFor continually checks 'fn' as driven by 'wait'.

WaitFor gets a channel from 'wait()”, and then invokes 'fn' once for every value placed on the channel and once more when the channel is closed.

If 'fn' returns an error the loop ends and that error is returned, and if 'fn' returns true the loop ends and nil is returned.

ErrWaitTimeout will be returned if the channel is closed without fn ever returning true.

Types

type Backoff

type Backoff struct {
	Duration time.Duration // the base duration
	Factor   float64       // Duration is multipled by factor each iteration
	Jitter   float64       // The amount of jitter applied each iteration
	Steps    int           // Exit with error after this many steps
}

Backoff holds parameters applied to a Backoff function.

type ConditionFunc

type ConditionFunc func() (done bool, err error)

ConditionFunc returns true if the condition is satisfied, or an error if the loop should be aborted.

type WaitFunc

type WaitFunc func(done <-chan struct{}) <-chan struct{}

WaitFunc creates a channel that receives an item every time a test should be executed and is closed when the last test should be invoked.