opt: shrink the ring-buffer for saving memory

eventloop_unix.go

@@ -49,7 +49,7 @@ type internalEventloop struct {
 	idx               int                     // loop index in the server loops list
 	svr               *server                 // server in loop
 	poller            *netpoll.Poller         // epoll or kqueue
-	packet            []byte                  // read packet buffer
+	packet            []byte                  // read packet buffer whose capacity is 64KB
 	connCount         int32                   // number of active connections in event-loop
 	connections       map[int]*conn           // loop connections fd -> conn
 	eventHandler      EventHandler            // user eventHandler

ringbuffer/ring_buffer.go

@@ -118,9 +118,6 @@ func (r *RingBuffer) Shift(n int) {
 
 	if n < r.Length() {
 		r.r = (r.r + n) & r.mask
-		if r.r == r.w {
-			r.isEmpty = true
-		}
 	} else {
 		r.Reset()
 	}
@@ -154,7 +151,7 @@ func (r *RingBuffer) Read(p []byte) (n int, err error) {
 		copy(p, r.buf[r.r:r.r+n])
 		r.r += n
 		if r.r == r.w {
-			r.isEmpty = true
+			r.Reset()
 		}
 		return
 	}
@@ -174,7 +171,7 @@ func (r *RingBuffer) Read(p []byte) (n int, err error) {
 	}
 	r.r = (r.r + n) & r.mask
 	if r.r == r.w {
-		r.isEmpty = true
+		r.Reset()
 	}
 
 	return n, err
@@ -191,7 +188,7 @@ func (r *RingBuffer) ReadByte() (b byte, err error) {
 		r.r = 0
 	}
 	if r.r == r.w {
-		r.isEmpty = true
+		r.Reset()
 	}
 
 	return b, err
@@ -370,24 +367,30 @@ func (r *RingBuffer) IsEmpty() bool {
 
 // Reset the read pointer and writer pointer to zero.
 func (r *RingBuffer) Reset() {
-	r.r = 0
-	r.w = 0
 	r.isEmpty = true
+	r.r, r.w = 0, 0
+
+	// Shrink the internal buffer for saving memory.
+	newCap := r.size / 2
+	newBuf := make([]byte, newCap)
+	r.buf = newBuf
+	r.size = newCap
+	r.mask = newCap - 1
 }
 
 func (r *RingBuffer) malloc(cap int) {
 	var newCap int
-	if r.size == 0 && initSize >= cap {
+	if r.size == 0 && cap < initSize {
 		newCap = initSize
 	} else {
 		newCap = internal.CeilToPowerOfTwo(r.size + cap)
 	}
 	newBuf := make([]byte, newCap)
 	oldLen := r.Length()
 	_, _ = r.Read(newBuf)
+	r.buf = newBuf
 	r.r = 0
 	r.w = oldLen
 	r.size = newCap
 	r.mask = newCap - 1
-	r.buf = newBuf
 }

ringbuffer/ring_buffer_test.go

@@ -144,6 +144,7 @@ func TestRingBuffer_Write(t *testing.T) {
 	}
 
 	rb.Reset()
+	size = rb.Cap()
 	// write 4 * 2 = 8 bytes
 	n, _ = rb.Write([]byte(strings.Repeat("abcd", 2)))
 	if n != 8 {
@@ -264,6 +265,7 @@ func TestRingBuffer_Read(t *testing.T) {
 
 	// write 16 bytes to read
 	_, _ = rb.Write([]byte(strings.Repeat("abcd", 4)))
+	// read all data from buffer, it will be shrunk from 64 to 32.
 	n, err = rb.Read(buf)
 	if err != nil {
 		t.Fatalf("read failed: %v", err)
@@ -274,15 +276,16 @@ func TestRingBuffer_Read(t *testing.T) {
 	if rb.Length() != 0 {
 		t.Fatalf("expect len 0 bytes but got %d. r.w=%d, r.r=%d", rb.Length(), rb.w, rb.r)
 	}
-	if rb.Free() != 64 {
+	if rb.Free() != 32 {
 		t.Fatalf("expect free 64 bytes but got %d. r.w=%d, r.r=%d", rb.Free(), rb.w, rb.r)
 	}
-	if rb.r != 16 {
-		t.Fatalf("expect r.r=16 but got %d. r.w=%d", rb.r, rb.w)
+	if rb.r != 0 {
+		t.Fatalf("expect r.r=0 but got %d. r.w=%d", rb.r, rb.w)
 	}
 
-	// write long slice to read, it will scale from 64 to 128 bytes.
+	// write long slice to read, it will scale from 32 to 128 bytes.
 	_, _ = rb.Write([]byte(strings.Repeat("abcd", 20)))
+	// read all data from buffer, it will be shrunk from 128 to 64.
 	n, err = rb.Read(buf)
 	if err != nil {
 		t.Fatalf("read failed: %v", err)
@@ -293,11 +296,11 @@ func TestRingBuffer_Read(t *testing.T) {
 	if rb.Length() != 0 {
 		t.Fatalf("expect len 0 bytes but got %d. r.w=%d, r.r=%d", rb.Length(), rb.w, rb.r)
 	}
-	if rb.Free() != 128 {
+	if rb.Free() != 64 {
 		t.Fatalf("expect free 128 bytes but got %d. r.w=%d, r.r=%d", rb.Free(), rb.w, rb.r)
 	}
-	if rb.r != 80 {
-		t.Fatalf("expect r.r=80 but got %d. r.w=%d", rb.r, rb.w)
+	if rb.r != 0 {
+		t.Fatalf("expect r.r=0 but got %d. r.w=%d", rb.r, rb.w)
 	}
 
 	rb.Reset()
@@ -374,7 +377,7 @@ func TestRingBuffer_ByteInterface(t *testing.T) {
 		t.Fatalf("expect IsFull is false but got true")
 	}
 
-	// write to, isFull
+	// write two, isFull
 	_ = rb.WriteByte('b')
 	if rb.Length() != 2 {
 		t.Fatalf("expect len 2 bytes but got %d. r.w=%d, r.r=%d", rb.Length(), rb.w, rb.r)
@@ -461,7 +464,7 @@ func TestRingBuffer_ByteInterface(t *testing.T) {
 	if rb.Length() != 0 {
 		t.Fatalf("expect len 0 byte but got %d. r.w=%d, r.r=%d", rb.Length(), rb.w, rb.r)
 	}
-	if rb.Free() != 4 {
+	if rb.Free() != 2 {
 		t.Fatalf("expect free 4 byte but got %d. r.w=%d, r.r=%d", rb.Free(), rb.w, rb.r)
 	}
 	// check empty or full
@@ -472,3 +475,23 @@ func TestRingBuffer_ByteInterface(t *testing.T) {
 		t.Fatalf("expect IsFull is false but got true")
 	}
 }
+
+func TestShrinkBuffer(t *testing.T) {
+	testStr := "Hello World!"
+	testCap := 1024
+
+	rb := New(testCap)
+	_, _ = rb.WriteString(testStr)
+	rb.LazyReadAll()
+	rb.Shift(len(testStr))
+	if rb.Cap() != testCap/2 {
+		t.Fatalf("expect buffer capacity %d, but got %d", testCap/2, rb.Cap())
+	}
+
+	_, _ = rb.WriteString(testStr)
+	rb.LazyReadAll()
+	rb.Reset()
+	if rb.Cap() != testCap/4 {
+		t.Fatalf("expect buffer capacity %d, but got %d", testCap/4, rb.Cap())
+	}
+}