kqueue: wait without timeout

As noted in #24, reading from the kqueue won't unblock when
it is closed on all platforms. This commit solves the issue by
additionally watching on a pipe which is closed when Watcher
is closed. The read timeout is no longer necessary.

kqueue.go

@@ -14,16 +14,15 @@ import (
 	"path/filepath"
 	"sync"
 	"syscall"
-	"time"
 )
 
 // Watcher watches a set of files, delivering events to a channel.
 type Watcher struct {
 	Events chan Event
 	Errors chan error
-	done   chan bool // Channel for sending a "quit message" to the reader goroutine
 
-	kq int // File descriptor (as returned by the kqueue() syscall).
+	kq        int    // File descriptor (as returned by the kqueue() syscall).
+	closepipe [2]int // Pipe used for closing.
 
 	mu              sync.Mutex        // Protects access to watcher data
 	watches         map[string]int    // Map of watched file descriptors (key: path).
@@ -41,21 +40,21 @@ type pathInfo struct {
 
 // NewWatcher establishes a new watcher with the underlying OS and begins waiting for events.
 func NewWatcher() (*Watcher, error) {
-	kq, err := kqueue()
+	kq, closepipe, err := kqueue()
 	if err != nil {
 		return nil, err
 	}
 
 	w := &Watcher{
 		kq:              kq,
+		closepipe:       closepipe,
 		watches:         make(map[string]int),
 		dirFlags:        make(map[string]uint32),
 		paths:           make(map[int]pathInfo),
 		fileExists:      make(map[string]bool),
 		externalWatches: make(map[string]bool),
 		Events:          make(chan Event),
 		Errors:          make(chan error),
-		done:            make(chan bool),
 	}
 
 	go w.readEvents()
@@ -88,8 +87,8 @@ func (w *Watcher) Close() error {
 		}
 	}
 
-	// Send "quit" message to the reader goroutine:
-	w.done <- true
+	// Send "quit" message to the reader goroutine.
+	syscall.Close(w.closepipe[1])
 
 	return nil
 }
@@ -154,9 +153,6 @@ func (w *Watcher) Remove(name string) error {
 // Watch all events (except NOTE_EXTEND, NOTE_LINK, NOTE_REVOKE)
 const noteAllEvents = syscall.NOTE_DELETE | syscall.NOTE_WRITE | syscall.NOTE_ATTRIB | syscall.NOTE_RENAME
 
-// keventWaitTime to block on each read from kevent
-var keventWaitTime = durationToTimespec(100 * time.Millisecond)
-
 // addWatch adds name to the watched file set.
 // The flags are interpreted as described in kevent(2).
 // Returns the real path to the file which was added, if any, which may be different from the one passed in the case of symlinks.
@@ -264,34 +260,35 @@ func (w *Watcher) addWatch(name string, flags uint32) (string, error) {
 // Event values that it sends down the Events channel.
 func (w *Watcher) readEvents() {
 	eventBuffer := make([]syscall.Kevent_t, 10)
-
-	for {
-		// See if there is a message on the "done" channel
-		select {
-		case <-w.done:
-			err := syscall.Close(w.kq)
-			if err != nil {
-				w.Errors <- err
-			}
-			close(w.Events)
-			close(w.Errors)
-			return
-		default:
+	defer func() {
+		err := syscall.Close(w.kq)
+		if err != nil {
+			w.Errors <- err
 		}
+		syscall.Close(w.closepipe[0])
+		close(w.Events)
+		close(w.Errors)
+	}()
 
-		// Get new events
-		kevents, err := read(w.kq, eventBuffer, &keventWaitTime)
+	for closed := false; !closed; {
+		kevents, err := read(w.kq, eventBuffer)
 		// EINTR is okay, the syscall was interrupted before timeout expired.
 		if err != nil && err != syscall.EINTR {
 			w.Errors <- err
 			continue
 		}
 
 		// Flush the events we received to the Events channel
-		for len(kevents) > 0 {
-			kevent := &kevents[0]
+		for _, kevent := range kevents {
 			watchfd := int(kevent.Ident)
 			mask := uint32(kevent.Fflags)
+			// Shut down the loop when the pipe is closed,
+			// but only after all other events have been processed.
+			if watchfd == w.closepipe[0] {
+				closed = true
+				continue
+			}
+
 			w.mu.Lock()
 			path := w.paths[watchfd]
 			w.mu.Unlock()
@@ -346,9 +343,6 @@ func (w *Watcher) readEvents() {
 					}
 				}
 			}
-
-			// Move to next event
-			kevents = kevents[1:]
 		}
 	}
 }
@@ -460,12 +454,24 @@ func (w *Watcher) internalWatch(name string, fileInfo os.FileInfo) (string, erro
 }
 
 // kqueue creates a new kernel event queue and returns a descriptor.
-func kqueue() (kq int, err error) {
+func kqueue() (kq int, closepipe [2]int, err error) {
 	kq, err = syscall.Kqueue()
 	if kq == -1 {
-		return kq, err
+		return kq, closepipe, err
+	}
+	// Register the close pipe.
+	if err := syscall.Pipe(closepipe[:]); err != nil {
+		syscall.Close(kq)
+		return kq, closepipe, err
 	}
-	return kq, nil
+	events := make([]syscall.Kevent_t, 1)
+	const pflag = syscall.EV_ADD | syscall.EV_ENABLE | syscall.EV_ONESHOT
+	syscall.SetKevent(&events[0], closepipe[0], syscall.EVFILT_READ, pflag)
+	if ok, err := syscall.Kevent(kq, events, nil, nil); ok == -1 {
+		syscall.Close(kq)
+		return kq, closepipe, err
+	}
+	return kq, closepipe, nil
 }
 
 // register events with the queue
@@ -488,15 +494,10 @@ func register(kq int, fds []int, flags int, fflags uint32) error {
 
 // read retrieves pending events, or waits until an event occurs.
 // A timeout of nil blocks indefinitely, while 0 polls the queue.
-func read(kq int, events []syscall.Kevent_t, timeout *syscall.Timespec) ([]syscall.Kevent_t, error) {
-	n, err := syscall.Kevent(kq, nil, events, timeout)
+func read(kq int, events []syscall.Kevent_t) ([]syscall.Kevent_t, error) {
+	n, err := syscall.Kevent(kq, nil, events, nil)
 	if err != nil {
 		return nil, err
 	}
 	return events[0:n], nil
 }
-
-// durationToTimespec prepares a timeout value
-func durationToTimespec(d time.Duration) syscall.Timespec {
-	return syscall.NsecToTimespec(d.Nanoseconds())
-}