diff --git a/watcher.go b/watcher.go
index fb165f7..bb190cb 100644
--- a/watcher.go
+++ b/watcher.go
@@ -21,15 +21,15 @@ type aiocb struct {
 	done   chan OpResult
 }
 
-// OpResult of operation
+// OpResult is the result of an aysnc-io
 type OpResult struct {
-	Fd     int
+	Fd     int    // related file descriptor to this result
 	Buffer []byte // the original committed buffer
-	Size   int
-	Err    error
+	Size   int    // number of bytes sent or received
+	Err    error  // IO error
 }
 
-// Watcher will monitor events and process Request(s)
+// Watcher will monitor events and process async-io request(s),
 type Watcher struct {
 	pfd *poller // poll fd
 
@@ -41,7 +41,7 @@ type Watcher struct {
 	chWriters         chan aiocb
 
 	// internal buffer for reading
-	swapbuffer chan []byte
+	swapBuffer chan []byte
 
 	die     chan struct{}
 	dieOnce sync.Once
@@ -51,7 +51,7 @@ type Watcher struct {
 	connsLock sync.Mutex
 }
 
-// CreateWatcher creates a management object for monitoring events of net.Conn
+// CreateWatcher creates a management object for monitoring file descriptors
 func CreateWatcher(bufsize int) (*Watcher, error) {
 	w := new(Watcher)
 	pfd, err := openPoll()
@@ -60,17 +60,20 @@ func CreateWatcher(bufsize int) (*Watcher, error) {
 	}
 	w.pfd = pfd
 
-	w.swapbuffer = make(chan []byte, 2)
-	for i := 0; i < cap(w.swapbuffer); i++ {
-		w.swapbuffer <- make([]byte, bufsize)
+	// swapBuffer for concurrent read
+	w.swapBuffer = make(chan []byte, 2)
+	for i := 0; i < cap(w.swapBuffer); i++ {
+		w.swapBuffer <- make([]byte, bufsize)
 	}
 
+	// loop related chan
 	w.chReadableNotify = make(chan int)
 	w.chWritableNotify = make(chan int)
 	w.chStopWatchNotify = make(chan int)
 	w.chReaders = make(chan aiocb)
 	w.chWriters = make(chan aiocb)
 
+	// hold net.Conn only
 	w.conns = make(map[int]net.Conn)
 	w.die = make(chan struct{})
 
@@ -80,15 +83,18 @@ func CreateWatcher(bufsize int) (*Watcher, error) {
 }
 
 // Close stops monitoring on events for all connections
-func (w *Watcher) Close() error {
+func (w *Watcher) Close() (err error) {
 	w.dieOnce.Do(func() {
 		close(w.die)
+		err = w.pfd.Close()
 	})
-	return w.pfd.Close()
+	return err
 }
 
-// Watch starts watching events on connection `conn`
+// Watch starts watching events on `conn`, and returns a file descriptor
+// for following IO operations.
 func (w *Watcher) Watch(conn net.Conn) (fd int, err error) {
+	// get file descriptor
 	c, ok := conn.(interface {
 		SyscallConn() (syscall.RawConn, error)
 	})
@@ -115,7 +121,7 @@ func (w *Watcher) Watch(conn net.Conn) (fd int, err error) {
 	// poll this fd
 	w.pfd.Watch(fd)
 
-	// prevent GC net.Conn
+	// prevent conn from GC
 	w.connsLock.Lock()
 	w.conns[fd] = conn
 	w.connsLock.Unlock()
@@ -135,7 +141,7 @@ func (w *Watcher) StopWatch(fd int) {
 	}
 }
 
-// Read submits a read requests and notify with done, cap(done) must 0
+// Read submits a read requests and notify with done, the cap(done) must be 0, i.e unbuffered chan.
 func (w *Watcher) Read(fd int, done chan OpResult) error {
 	if cap(done) != 0 {
 		return ErrBufferedChan
@@ -148,7 +154,7 @@ func (w *Watcher) Read(fd int, done chan OpResult) error {
 	}
 }
 
-// Write submits a write requests and notify with done
+// Write submits a write requests and notify with done, the cap(done) must be 0, i.e unbuffered chan.
 func (w *Watcher) Write(fd int, buf []byte, done chan OpResult) error {
 	// do nothing
 	if len(buf) == 0 {
@@ -168,10 +174,10 @@ func (w *Watcher) Write(fd int, buf []byte, done chan OpResult) error {
 }
 
 // tryRead will try to read data on aiocb and notify
-// returns true if io has completed, false means EAGAIN
+// returns true if io has completed, false means not.
 func (w *Watcher) tryRead(pcb *aiocb) (complete bool) {
-	buf := <-w.swapbuffer
-	defer func() { w.swapbuffer <- buf }()
+	buf := <-w.swapBuffer
+	defer func() { w.swapBuffer <- buf }()
 
 	nr, er := syscall.Read(pcb.fd, buf)
 	if er == syscall.EAGAIN {
@@ -189,10 +195,12 @@ func (w *Watcher) tryWrite(pcb *aiocb) (complete bool) {
 		return false
 	}
 
+	// if ew is nil, accumulate bytes written
 	if ew == nil {
 		pcb.size += nw
 	}
 
+	// all bytes written or has error
 	if pcb.size == len(pcb.buffer) || ew != nil {
 		if pcb.done != nil {
 			pcb.done <- OpResult{Fd: pcb.fd, Buffer: pcb.buffer, Size: nw, Err: ew}
@@ -202,6 +210,7 @@ func (w *Watcher) tryWrite(pcb *aiocb) (complete bool) {
 	return false
 }
 
+// the core event loop of this watcher
 func (w *Watcher) loop() {
 	pendingReaders := make(map[int][]aiocb)
 	pendingWriters := make(map[int][]aiocb)