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fswatch.go
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fswatch.go
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package main
import (
"context"
"sync/atomic"
"time"
"github.com/fsnotify/fsnotify"
"github.com/rsms/memex/extension"
)
// event op (bitmask)
const (
FSEventCreate = extension.FSEventCreate
FSEventWrite = extension.FSEventWrite
FSEventRemove = extension.FSEventRemove
FSEventRename = extension.FSEventRename
FSEventChmod = extension.FSEventChmod
)
type FSEvent = extension.FSEvent
type FSEventFlags = extension.FSEventFlags
// FSWatcher observes file system for changes.
// A new FSWatcher starts in Resumed mode.
type FSWatcher struct {
Latency time.Duration // Time window for bundling changes together. Default: 100ms
Events chan []FSEvent // Channel on which event batches are delivered
Error error // After Events channel is closed, this indicates the reason
w *fsnotify.Watcher
start uint32
ctx context.Context
}
func NewFSWatcher(ctx context.Context) (*FSWatcher, error) {
w2, err := fsnotify.NewWatcher()
if err != nil {
// fails only when the underlying OS extension fails.
// E.g. golang.org/x/sys/unix.{Kqueue,InotifyInit1} or syscall.CreateIoCompletionPort
return nil, err
}
w := &FSWatcher{
Latency: 100 * time.Millisecond,
Events: make(chan []FSEvent),
w: w2,
ctx: ctx,
}
return w, nil
}
// Add file or directory (non-recursively) to be watched.
// If path is already watched nil is returned (duplicates ignored.)
func (w *FSWatcher) Add(path string) error {
err := w.w.Add(path)
if err == nil && atomic.CompareAndSwapUint32(&w.start, 0, 1) {
go w.runLoop()
}
return err
}
// Remove unregisters a file or directory that was previously registered with Add.
// If path is not being watched an error is returned.
func (w *FSWatcher) Remove(path string) error {
return w.w.Remove(path)
}
// Stop begins the shutdown process of the watcher. Causes Run() to return.
func (w *FSWatcher) Close() error {
if atomic.CompareAndSwapUint32(&w.start, 0, 1) {
// never started so w.Events would not close from runLoop exiting
close(w.Events)
}
err := w.w.Close()
if err == nil {
err = w.Error
}
return err
}
func (w *FSWatcher) runLoop() {
changeq := make(map[string]FSEventFlags)
foreverDuration := time.Duration(0x7fffffffffffffff)
flushTimer := time.NewTimer(foreverDuration)
flushTimerActive := false
var errCounter int
defer close(w.Events)
for {
select {
case <-w.ctx.Done():
w.Error = w.ctx.Err()
return
case <-flushTimer.C:
if len(changeq) > 0 {
// logd("[fswatcher] flush %+v", changeq)
events := make([]FSEvent, 0, len(changeq))
for name, flags := range changeq {
events = append(events, FSEvent{
Flags: flags,
Name: name,
})
}
for _, ev := range events {
delete(changeq, ev.Name)
}
w.Events <- events
}
flushTimer.Reset(foreverDuration)
flushTimerActive = false
case event, more := <-w.w.Events:
if !more {
// closed
return
}
// logd("[fswatcher] event: %v %q", event.Op, event.Name)
// reset error counter
errCounter = 0
// update event mask
prev := changeq[event.Name]
next := FSEventFlags(event.Op)
if prev&FSEventCreate != 0 && next&FSEventRemove != 0 && next&FSEventCreate == 0 {
// was created and is now removed
next = ((prev | next) &^ FSEventCreate) &^ FSEventWrite
} else if prev&FSEventRemove != 0 && next&FSEventCreate != 0 && next&FSEventRemove == 0 {
// was removed and is now created -> modified
next = (prev | FSEventWrite) &^ FSEventRemove
} else {
next = prev | next
}
changeq[event.Name] = next
if !flushTimerActive {
flushTimerActive = true
flushTimer.Reset(w.Latency)
}
case err := <-w.w.Errors:
w.Error = err
errCounter++
if errCounter > 10 {
// There were many errors without any file events.
// Close the watcher and return as there may be unrecoverable
w.Close()
return
}
} // select
}
}