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idle.go
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idle.go
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// Package idle helps to gracefully shutdown idle (typically http) servers
package idle
import (
"fmt"
"net/http"
"sync/atomic"
"time"
)
var (
// For simple servers without backgroud jobs, global singleton for simpler API
// Enter/Exit worn't work for global idler as Enter may be called before Wait, use CreateIdler in those cases
gIdler atomic.Pointer[idler]
)
// Wait waits till the server is idle and returns. i.e. no Ticks in last <timeout> duration
func Wait(timeout time.Duration) error {
i := CreateIdler(timeout).(*idler)
ok := gIdler.CompareAndSwap(nil, i)
if !ok {
return fmt.Errorf("idler already waiting")
}
i.Wait()
return nil
}
// Tick records the current time. This will make the server not idle until next Tick or timeout
func Tick() {
i := gIdler.Load()
if i != nil {
i.Tick()
}
}
// WrapHandler calls Tick() before processing passing request to http.Handler
func WrapHandler(h http.Handler) http.Handler {
if h == nil {
h = http.DefaultServeMux
}
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
Tick()
h.ServeHTTP(w, r)
})
}
// WrapIdlerHandler calls idler.Tick() before processing passing request to http.Handler
func WrapIdlerHandler(i Idler, h http.Handler) http.Handler {
if h == nil {
h = http.DefaultServeMux
}
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
i.Tick()
h.ServeHTTP(w, r)
})
}
// Idler helps manage idle servers
type Idler interface {
// Tick records the current time. This will make the server not idle until next Tick or timeout
Tick()
// Wait waits till the server is idle and returns. i.e. no Ticks in last <timeout> duration
Wait()
// For long running background jobs, use Enter to record start time. Wait will not return while there are active jobs running
Enter()
// Exit records end of a background job
Exit()
// Get the channel to wait yourself
Chan() <-chan struct{}
}
type idler struct {
lastTick atomic.Pointer[time.Time]
c chan struct{}
active atomic.Int64
}
func (i *idler) Enter() {
i.active.Add(1)
}
func (i *idler) Exit() {
i.Tick()
i.active.Add(-1)
}
// CreateIdler creates an Idler with given timeout
func CreateIdler(timeout time.Duration) Idler {
i := &idler{}
i.c = make(chan struct{})
i.Tick()
go func() {
for {
if i.active.Load() != 0 {
time.Sleep(timeout)
continue
}
t := *i.lastTick.Load()
now := time.Now()
dur := t.Add(timeout).Sub(now)
if dur == dur.Abs() {
time.Sleep(dur)
continue
}
break
}
close(i.c)
}()
return i
}
func (i *idler) Tick() {
now := time.Now()
i.lastTick.Store(&now)
}
func (i *idler) Wait() {
<-i.c
}
func (i *idler) Chan() <-chan struct{} {
return i.c
}