blob: 42b654c60f6ca536e61131ffeafb806f27853a00 [file] [log] [blame]
// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package poller supports periodic polling to load a value.
package poller
import (
// A Getter returns a value.
type Getter func(context.Context) (any, error)
// A Poller maintains a current value, and refreshes it by periodically
// polling for a new value.
type Poller struct {
getter Getter
onError func(error)
mu sync.Mutex
current any
// New creates a new poller with an initial value. The getter is invoked
// to obtain updated values. Errors returned from the getter are passed
// to onError.
func New(initial any, getter Getter, onError func(error)) *Poller {
return &Poller{
getter: getter,
onError: onError,
current: initial,
// Start begins polling in a separate goroutine, at the given period. To stop
// the goroutine, cancel the context passed to Start.
func (p *Poller) Start(ctx context.Context, period time.Duration) {
ticker := time.NewTicker(period)
go func() {
for {
select {
case <-ctx.Done():
case <-ticker.C:
ctx2, cancel := context.WithTimeout(ctx, period)
// Poll calls p's getter immediately and synchronously.
func (p *Poller) Poll(ctx context.Context) {
next, err := p.getter(ctx)
if err != nil {
} else {
p.current = next
// Current returns the current value. Initially, this is the value passed to New.
// After each successful poll, the value is updated.
// If a poll fails, the value remains unchanged.
func (p *Poller) Current() any {
return p.current