optimestamp.go

package main

import (
	"expvar"
	"github.com/duego/cryriver/mongodb"
	"log"
	"os"
	"time"
)

var (
	lastEsSeen     *mongodb.Timestamp
	lastEsSeenC    = make(chan *mongodb.Timestamp, 1)
	lastEsSeenStat = expvar.NewString("Last optime seen")
)

func init() {
	// Restore any previously saved timestamp
	lastEsSeen = new(mongodb.Timestamp)
	if f, err := os.Open(*optimeStore); err != nil {
		log.Println("Failed to load previous lastEsSeen timestamp:", err)
	} else {
		lastEsSeen.Load(f)
		f.Close()
	}
	go saveLastEsSeen()
}

// saveLastEsSeen loops the channel to save our progress on what timestamp we have seen so far.
// It will be flushed to disk when our timer ticks.
func saveLastEsSeen() {
	lastEsSeenTimer := time.NewTicker(time.Second)
	for {
		select {
		case <-lastEsSeenTimer.C:
			if lastEsSeen == nil {
				continue
			}
			if f, err := os.Create(*optimeStore); err != nil {
				log.Println("Error saving oplog timestamp:", err)
			} else {
				if err := lastEsSeen.Save(f); err != nil {
					log.Println("Error saving oplog timestamp:", err)
				}
				f.Close()
				lastEsSeenStat.Set(lastEsSeen.String())
				lastEsSeen = nil
			}
		case lastEsSeen = <-lastEsSeenC:
		}
	}
}