A data item that automatically saves data at a maximum rate of once every second, even if the data is changing much faster than that.

gistfile1.go

// A data item that automatically saves data at a maximum rate of once every second, 
// even if the data is changing much faster than that.

// I didn't write this code. It was created by Roger Peppe and sent to the 
// go-nuts mailing list. The original version is at http://play.golang.org/p/1LCxri0EXz

package main

import (
  "io/ioutil"
  "log"
  "sync"
  "time"
)

func main() {
  d := NewData()
  d.Set("a")
  d.Set("b")
  time.Sleep(250 * time.Millisecond)
  d.Set("c")
  time.Sleep(1000 * time.Millisecond)
  d.Set("d")
  time.Sleep(1100 * time.Millisecond)
}

type Data struct {
  mu  sync.Mutex
  changed  chan struct{}
  s  string
}
  
func NewData() *Data {
  d := &Data{
    changed: make(chan struct{}, 1),
  }
  go d.saver()
  return d
}

func (d *Data) Set(s string) {
  d.mu.Lock()
  defer d.mu.Unlock()
  d.s = s
  select {
  case d.changed <- struct{}{}:
  default:
  }
}

func (d *Data) Get() string {
  d.mu.Lock()
  defer d.mu.Unlock()
  return d.s
}

func (d *Data) saver() {
  for {
    <-d.changed
    timeout := time.After(1 * time.Second)
  wait:
    for {
      select {
      case <-d.changed:
      case <-timeout:
        s := d.Get()
        if err := ioutil.WriteFile("/tmp/saved_data", []byte(s), 0666); err != nil {
          log.Printf("failed to saved data: %v", err)
        } else {
          log.Printf("saved %q", s)
        }
        break wait
      }
    }
  }
}