how to repeat shutting down and establish go routine? - go

Question

every one,I am new to golang.I wanna get the data from log file generated by my application.cuz roll-back mechanism, I met some problem.For instance,my target log file is chats.log,it will be renamed to chats.log.2018xxx and a new chats.log will be created.so my go routine that read log file will fail to work.
so I need detect the change and shutdown the previous go routine and then establish the new go routine.
I looked for modules that can help me,and I found
func ExampleNewWatcher(fn string, createnoti chan string, wg sync.WaitGroup) {
wg.Add(1)
defer wg.Done()
watcher, err := fsnotify.NewWatcher()
if err != nil {
log.Fatal(err)
}
defer watcher.Close()
done := make(chan bool)
go func() {
for {
select {
case event := <-watcher.Events:
if event.Op == fsnotify.Create && event.Name==fn{
createnoti <- "has been created"
}
case err := <-watcher.Errors:
log.Println("error:", err)
}
}
}()
err = watcher.Add("./")
if err != nil {
log.Fatal(err)
}
<-done
}
I use fsnotify to detech the change,and make sure the event of file is my log file,and then send some message to a channel.
this is my worker go routine:
func tailer(fn string,isfollow bool, outchan chan string, done <-chan interface{},wg sync.WaitGroup) error {
wg.Add(1)
defer wg.Done()
_, err := os.Stat(fn)
if err != nil{
panic(err)
}
t, err := tail.TailFile(fn, tail.Config{Follow:isfollow})
if err != nil{
panic(err)
}
defer t.Stop()
for line := range t.Lines{
select{
case outchan <- line.Text:
case <- done:
return nil
}
}
return nil
}
I using tail module to read the log file,and I add a done channel to it to shutdown the cycle(I don't know whether I put it in the right way)
And I will send every log content to a channel to consuming it.
So here is the question:how should I put it together?
ps: Actually,I can use some tool to do this job.like apache-flume,but all of those tools need dependency.
Thank you a lot!

Answer 1

Here is a complete example that reloads and rereads the file as it changes or gets deleted and recreated:
package main
import (
"github.com/fsnotify/fsnotify"
"io/ioutil"
"log"
)
const filename = "myfile.txt"
func ReadFile(filename string) string {
data, err := ioutil.ReadFile(filename)
if err != nil {
log.Println(err)
}
return string(data)
}
func main() {
watcher, err := fsnotify.NewWatcher()
if err != nil {
log.Fatal(err)
}
defer watcher.Close()
err = watcher.Add("./")
if err != nil {
log.Fatal(err)
}
for {
select {
case event := <-watcher.Events:
if event.Op == fsnotify.Create && event.Name == filename {
log.Println(ReadFile(filename))
}
case err := <-watcher.Errors:
log.Println("error:", err)
}
}
}
Note this doesn't require goroutines, channels or a WaitGroup. Better to keep things simple and reserve those for when they're actually needed.