fsevents can't watch more than 4096 files (repro)

main.go

package main

import (
	"log"
	"os"
	"os/signal"
	"syscall"
	"time"

	"github.com/tilt-dev/fsevents"
)

func main() {
	args := os.Args[1:]
	if len(args) == 0 {
		log.Fatal("Pass at least one filepath to watch")
	}

	stop := make(chan bool)
	watchForExit(stop)

	stream := newStream(args)
	log.Printf("Watching %d paths", len(stream.Paths))
	stream.Start()

	for {
		select {
		case <-stop:
			stream.Stop()
			return
		case events, ok := <-stream.Events:
			if !ok {
				return
			}
			for _, e := range events {
				log.Printf("- %s", e.Path)
			}
		}

	}
}

func newStream(paths []string) *fsevents.EventStream {
	stream := &fsevents.EventStream{
		Latency: 1 * time.Millisecond,
		Flags:   fsevents.FileEvents,
		EventID: fsevents.LatestEventID(),
	}
	for _, p := range paths {
		stream.Paths = append(stream.Paths, p)
	}

	return stream
}

func watchForExit(stopChan chan bool) {
	sigs := make(chan os.Signal, 1)
	signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM)
	go func() {
		<-sigs
		stopChan <- true // send stop signal

		// If we get another SIGINT/SIGTERM, OR it takes too long to exit
		// after sending signal, just quit
		select {
		case <-sigs:
			log.Println("force quitting...")
			os.Exit(1)
		case <-time.After(2 * time.Second):
			log.Println("Stop signal sent but app still running; forcibly exiting.")
			os.Exit(1)
		}
	}()
}

repro.md

1. Copy main.go above
2. create directory with a bunch of files:

   mkdir files
   for i in {1..4095}; do touch files/$i; done
   

3. Confirm that you can successfully watch this many files:
   • go run main.go $(find ./files)
   • See log message "Watching 4096 paths"
   • Change a file (e.g. touch files/123) and see the Go util report the change
4. Add another file:

   touch files/one-too-many
   

5. Observe that filewatching is now broken??
   • go run main.go $(find ./files)
   • See log message "Watching 4097 paths"
   • Change a file (e.g. touch files/456); this change is NOT reported by the Go util