Hello stackoverflow community, I am using github.com/fsnotify/fsnotify to set watchers to a file in Go. My function looks like
func SetWatcher(filename string) {
fmt.Println("Setting watcher to file ", filename)
Watcher, err = fsnotify.NewWatcher()
if err != nil {
fmt.Println("inotify errored. Other methods needs to be implemented.")
panic(err)
}
if err != nil {
log.Fatal(err)
}
done := make(chan bool)
go func() {
for {
select {
case event := <-Watcher.Events:
if event.Op == fsnotify.Remove {
fmt.Println("File removed, needs to kill the process.")
} else if event.Op == fsnotify.Rename {
fmt.Println("File renamed, need to restart seeking.")
}
case err := <-Watcher.Errors:
log.Println("error:", err)
}
}
}()
err = Watcher.Add(filename)
if err != nil {
log.Fatal(err)
}
<-done
}
which works so far and I get outputs as
Setting watcher to file /var/log/syslog
File renamed, need to restart seeking.
However, if I try to remove the closure running in the goroutine and run it as
func SetWatcher(filename string) {
fmt.Println("Setting watcher to file ", filename)
Watcher, err = fsnotify.NewWatcher()
if err != nil {
fmt.Println("inotify errored. Other methods needs to be implemented.")
panic(err)
}
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.Remove {
fmt.Println("File removed, needs to kill the process.")
} else if event.Op == fsnotify.Rename {
fmt.Println("File renamed, need to restart seeking.")
}
case err := <-Watcher.Errors:
log.Println("error:", err)
}
//}
//}()
err = Watcher.Add(filename)
if err != nil {
log.Fatal(err)
}
//<-done
}
the program never outputs anything. I ran it with strace
and the program is seen stuck at
[pid 5773] pselect6(0, NULL, NULL, NULL, {tv_sec=0, tv_nsec=20000}, NULL <unfinished ...>
[pid 5772] epoll_wait(4, [], 128, 0) = 0
[pid 5772] futex(0x598bf8, FUTEX_WAIT, 0, NULL <unfinished ...>
[pid 5773] <... pselect6 resumed> ) = 0 (Timeout)
[pid 5740] <... pselect6 resumed> ) = 0 (Timeout)
[pid 5773] futex(0x598578, FUTEX_WAIT, 0, {tv_sec=60, tv_nsec=0}
<unfinished ...>
[pid 5740] futex(0xae1f58, FUTEX_WAIT, 0, {tv_sec=60, tv_nsec=0}
and not receiving from the channel and keeps on waiting.
I've read that this could be caused because of non-buffered channel. So to validate that, I modified the library to use a buffered channel and the part of the function that generates the new watcher looks like
w := &Watcher{
fd: fd,
poller: poller,
watches: make(map[string]*watch),
paths: make(map[int]string),
Events: make(chan Event, 10), // Made it buffered here
Errors: make(chan error),
done: make(chan struct{}),
doneResp: make(chan struct{}),
}
But the behavior is the same. Can someone please help me understand why the reading from channel worked when it was in a goroutine, and didn't work without a goroutine?
Thank you.