feat(notify): New functionality for notify callback.

Reviewed-on: #3

multiread_test.go

@@ -6,6 +6,7 @@ import (
 	"math/rand"
 	"sync"
 	"testing"
+	"time"
 )
 
 func TestMultiRead(t *testing.T) {
@@ -226,3 +227,65 @@ func TestReaderClose(t *testing.T) {
 	}
 
 }
+
+func TestNotify(t *testing.T) {
+	src := make([]byte, 16)
+	_, _ = rand.Read(src)
+
+	wg := &sync.WaitGroup{}
+	cr := make(chan int, 3)
+	m := NewMultiReader(0)
+	r := make([]*Reader, 0)
+	r = append(r, m.NewReader(), m.NewReader(), m.NewReader())
+	for i := range r {
+		r[i].NotifyFunc(func(ix int) {
+			wg.Add(1)
+			defer wg.Done()
+			cr <- ix
+		})
+	}
+	_, _ = m.Write(src)
+	time.Sleep(time.Millisecond)
+	wg.Wait()
+
+	nctr := 0
+	stop := false
+	for !stop {
+		select {
+		case rd := <-cr:
+			nctr++
+			if rd != 16 {
+				t.Error("unexpected notify value")
+			}
+		default:
+			stop = true
+		}
+	}
+	if nctr != 3 {
+		t.Error("unexpected number of notify event")
+	}
+
+	_, _ = r[0].Seek(16, io.SeekCurrent)
+	_, _ = r[1].Seek(8, io.SeekCurrent)
+	_, _ = r[2].Seek(16, io.SeekCurrent)
+
+	_, _ = m.Write(src[:8])
+	time.Sleep(time.Millisecond)
+	wg.Wait()
+	stop = false
+	nctr = 0
+	for !stop {
+		select {
+		case rd := <-cr:
+			nctr++
+			if rd != 8 {
+				t.Error("unexpected notify value")
+			}
+		default:
+			stop = true
+		}
+	}
+	if nctr != 2 {
+		t.Error("unexpected number of notify event")
+	}
+}

multireader.go

@@ -20,6 +20,7 @@ type MultiReader struct {
 	buffer       []byte
 	readers      []*Reader
 	pos          []*Reader
+	notif        []*Reader
 	lastWritePos int
 	closed       bool
 }
@@ -28,11 +29,13 @@ type Reader struct {
 	multiReader *MultiReader
 	mtx         *sync.Mutex
 	cond        *sync.Cond
+	notify      func(int)
 	id          int
 	readPos     int
 	closed      bool
 }
 
+//MultiReader initialize new MultiReader object. The object also implements WriteCloser.
 func NewMultiReader(len int) *MultiReader {
 	if len < 0 {
 		len = 0
@@ -46,23 +49,39 @@ func NewMultiReader(len int) *MultiReader {
 		buffer:       buff,
 		readers:      make([]*Reader, 0),
 		pos:          make([]*Reader, 0),
+		notif:        make([]*Reader, 0),
 		lastWritePos: 0,
 		closed:       false,
 	}
 }
 
+func (m *MultiReader) notify(dataLen int) {
+	m.cond.Broadcast()
+	for _, reader := range m.notif {
+		if reader.notify != nil && reader.readPos >= m.lastWritePos-dataLen && !reader.closed {
+			go func() {
+				reader.notify(dataLen)
+			}()
+		}
+	}
+}
+
+// Write implements Writer interface. The function will not return error. Error return only satisfy the interface.
 func (m *MultiReader) Write(data []byte) (int, error) {
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
-	defer m.cond.Broadcast()
 
 	var (
 		tmpBuff []byte
+		dataLen int
 	)
 
 	if m.closed {
 		return 0, ErrMultiReaderClosed
 	}
+	defer func(ip *int) {
+		m.notify(*ip)
+	}(&dataLen)
 
 	if m.lastWritePos+len(data) > len(m.buffer) {
 		tmpBuff = make([]byte, m.lastWritePos+len(data)-len(m.buffer))
@@ -70,6 +89,8 @@ func (m *MultiReader) Write(data []byte) (int, error) {
 	}
 	copy(m.buffer[m.lastWritePos:], data)
 	m.lastWritePos += len(data)
+	dataLen = len(data)
+	//_ = dataLen //prevents lint complaining about ineffectual assignment
 
 	return len(data), nil
 }
@@ -116,6 +137,7 @@ func (m *MultiReader) removeReader(id int) {
 	m.pos = nb
 }
 
+// Close will not return error. The error return only satisfy the interface signature.
 func (m *MultiReader) Close() error {
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
@@ -123,6 +145,7 @@ func (m *MultiReader) Close() error {
 	return nil
 }
 
+// NewReader initialize new Reader object. The object implements ReadCloser and Seeker interface.
 func (m *MultiReader) NewReader() *Reader {
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
@@ -141,10 +164,44 @@ func (m *MultiReader) NewReader() *Reader {
 	return reader
 }
 
+// NotifyFunc sets up a callback function notify. The notify function will be called when there is a Write operation.
+// Notify function passed to the NotifyFunc will executed in a separate go routine for each notify function.
+// It's the caller responsibility to setup any synchronization to prevent data race.
+func (r *Reader) NotifyFunc(notify func(int)) {
+	r.mtx.Lock()
+	defer r.mtx.Unlock()
+
+	r.notify = notify
+
+	var x int
+	switch len(r.multiReader.notif) {
+	case 0:
+		r.multiReader.notif = append(r.multiReader.notif, r)
+	case 1:
+		if r.multiReader.notif[0].id != r.id {
+			goto notifyFuncAppend2
+		}
+	default:
+		goto notifyFuncAppend1
+	}
+	return
+
+notifyFuncAppend1:
+	x = sort.Search(len(r.multiReader.notif), func(i int) bool { return r.multiReader.notif[i].id >= r.id })
+	if x < len(r.multiReader.notif) && r.id == x {
+		return
+	}
+
+notifyFuncAppend2:
+	r.multiReader.notif = append(r.multiReader.notif, r)
+	sort.Slice(r.multiReader.notif, func(i, j int) bool { return r.multiReader.notif[i].id < r.multiReader.notif[j].id })
+}
+
+// Read implements Reader interface. If the reader reached the same position with the writer. It will wait.
+// Calling Read() is the same with calling WaitAvailable(), ReadAhead(), and Seek()
 func (r *Reader) Read(data []byte) (int, error) {
 	r.mtx.Lock()
 	defer r.mtx.Unlock()
-	defer r.cond.Broadcast()
 
 	var (
 		n   int
@@ -184,6 +241,8 @@ func (r *Reader) seek(offset int, whence int) (int, error) {
 	return r.readPos, nil
 }
 
+// Seek implements Seeker interface. The underlying function will move the reader position.
+// It only returns error when the whence parameter is not in io.SeekStart, io.SeekCurrent, io.SeekEnd
 func (r *Reader) Seek(offset int64, whence int) (int64, error) {
 	n, err := r.seek(int(offset), whence)
 	return int64(n), err
@@ -203,6 +262,7 @@ func (r *Reader) readAhead(data []byte) (int, error) {
 	return len(data), nil
 }
 
+// ReadAhead reads buffer ahead of current position without moving the reader position.
 func (r *Reader) ReadAhead(data []byte) (int, error) {
 	r.mtx.Lock()
 	defer r.mtx.Unlock()
@@ -215,9 +275,6 @@ func (r *Reader) waitAvailable() (int, error) {
 	}
 
 	for r.readPos >= r.multiReader.lastWritePos {
-		if r.closed {
-			return 0, ErrReaderClosed
-		}
 		if r.multiReader.closed {
 			return 0, ErrMultiReaderClosed
 		}
@@ -227,12 +284,14 @@ func (r *Reader) waitAvailable() (int, error) {
 	return r.multiReader.lastWritePos - r.readPos, nil
 }
 
+// WaitAvailable will only wait when Reader position reached Writer position.
 func (r *Reader) WaitAvailable() (int, error) {
 	r.mtx.Lock()
 	defer r.mtx.Unlock()
 	return r.waitAvailable()
 }
 
+// Close implements ReadCloser interface. It will not return error.
 func (r *Reader) Close() error {
 	r.mtx.Lock()
 	defer r.mtx.Unlock()