Add generic buffer.TypedRingGrowing and shrinkable buffer.Ring

buffer/ring_growing.go

@@ -16,31 +16,54 @@ limitations under the License.
 
 package buffer
 
+// RingGrowingOptions sets parameters for [RingGrowing] and
+// [TypedRingGrowing].
+type RingGrowingOptions struct {
+	// InitialSize is the number of pre-allocated elements in the
+	// initial underlying storage buffer.
+	InitialSize int
+}
+
 // RingGrowing is a growing ring buffer.
 // Not thread safe.
-type RingGrowing struct {
-	data     []interface{}
+//
+// Deprecated: Use TypedRingGrowing[any] instead.
+type RingGrowing = TypedRingGrowing[any]
+
+// NewRingGrowing constructs a new RingGrowing instance with provided parameters.
+//
+// Deprecated: Use NewTypedRingGrowing[any] instead.
+func NewRingGrowing(initialSize int) *RingGrowing {
+	return NewTypedRingGrowing[any](RingGrowingOptions{InitialSize: initialSize})
+}
+
+// TypedRingGrowing is a growing ring buffer.
+// The zero value has an initial size of 0 and is ready to use.
+// Not thread safe.
+type TypedRingGrowing[T any] struct {
+	data     []T
 	n        int // Size of Data
 	beg      int // First available element
 	readable int // Number of data items available
 }
 
-// NewRingGrowing constructs a new RingGrowing instance with provided parameters.
-func NewRingGrowing(initialSize int) *RingGrowing {
-	return &RingGrowing{
-		data: make([]interface{}, initialSize),
-		n:    initialSize,
+// NewTypedRingGrowing constructs a new TypedRingGrowing instance with provided parameters.
+func NewTypedRingGrowing[T any](opts RingGrowingOptions) *TypedRingGrowing[T] {
+	return &TypedRingGrowing[T]{
+		data: make([]T, opts.InitialSize),
+		n:    opts.InitialSize,
 	}
 }
 
 // ReadOne reads (consumes) first item from the buffer if it is available, otherwise returns false.
-func (r *RingGrowing) ReadOne() (data interface{}, ok bool) {
+func (r *TypedRingGrowing[T]) ReadOne() (data T, ok bool) {
 	if r.readable == 0 {
-		return nil, false
+		return
 	}
 	r.readable--
 	element := r.data[r.beg]
-	r.data[r.beg] = nil // Remove reference to the object to help GC
+	var zero T
+	r.data[r.beg] = zero // Remove reference to the object to help GC
 	if r.beg == r.n-1 {
 		// Was the last element
 		r.beg = 0
@@ -51,11 +74,14 @@ func (r *RingGrowing) ReadOne() (data interface{}, ok bool) {
 }
 
 // WriteOne adds an item to the end of the buffer, growing it if it is full.
-func (r *RingGrowing) WriteOne(data interface{}) {
+func (r *TypedRingGrowing[T]) WriteOne(data T) {
 	if r.readable == r.n {
 		// Time to grow
 		newN := r.n * 2
-		newData := make([]interface{}, newN)
+		if newN == 0 {
+			newN = 1
+		}
+		newData := make([]T, newN)
 		to := r.beg + r.readable
 		if to <= r.n {
 			copy(newData, r.data[r.beg:to])
@@ -72,11 +98,69 @@ func (r *RingGrowing) WriteOne(data interface{}) {
 }
 
 // Len returns the number of items in the buffer.
-func (r *RingGrowing) Len() int {
+func (r *TypedRingGrowing[T]) Len() int {
 	return r.readable
 }
 
 // Cap returns the capacity of the buffer.
-func (r *RingGrowing) Cap() int {
+func (r *TypedRingGrowing[T]) Cap() int {
 	return r.n
 }
+
+// RingGrowingOptions sets parameters for [Ring].
+type RingOptions struct {
+	// InitialSize is the number of pre-allocated elements in the
+	// initial underlying storage buffer.
+	InitialSize int
+	// NormalSize is the number of elements to allocate for new storage
+	// buffers once the Ring is consumed.
+	NormalSize int
+}
+
+// Ring is a dynamically-sized ring buffer which can grow and shrink as-needed.
+// The zero value has an initial size and normal size of 0 and is ready to use.
+// Not thread safe.
+type Ring[T any] struct {
+	growing    TypedRingGrowing[T]
+	normalSize int // Limits the size of the buffer that is kept for reuse. Read-only.
+}
+
+// NewRing constructs a new Ring instance with provided parameters.
+func NewRing[T any](opts RingOptions) *Ring[T] {
+	return &Ring[T]{
+		growing:    *NewTypedRingGrowing[T](RingGrowingOptions{InitialSize: opts.InitialSize}),
+		normalSize: opts.NormalSize,
+	}
+}
+
+// ReadOne reads (consumes) first item from the buffer if it is available,
+// otherwise returns false. When the buffer has been totally consumed and has
+// grown in size, it shrinks down to its initial size.
+func (r *Ring[T]) ReadOne() (data T, ok bool) {
+	element, ok := r.growing.ReadOne()
+
+	if r.growing.readable == 0 && r.growing.n > r.normalSize {
+		// The buffer is empty. Reallocate a new buffer so the old one can be
+		// garbage collected.
+		r.growing.data = make([]T, r.normalSize)
+		r.growing.n = r.normalSize
+		r.growing.beg = 0
+	}
+
+	return element, ok
+}
+
+// WriteOne adds an item to the end of the buffer, growing it if it is full.
+func (r *Ring[T]) WriteOne(data T) {
+	r.growing.WriteOne(data)
+}
+
+// Len returns the number of items in the buffer.
+func (r *Ring[T]) Len() int {
+	return r.growing.Len()
+}
+
+// Cap returns the capacity of the buffer.
+func (r *Ring[T]) Cap() int {
+	return r.growing.Cap()
+}

buffer/ring_growing_test.go

@@ -17,45 +17,163 @@ limitations under the License.
 package buffer
 
 import (
-	"reflect"
 	"testing"
 )
 
-func TestGrowth(t *testing.T) {
+func TestGrowthGrowing(t *testing.T) {
 	t.Parallel()
-	x := 10
-	g := NewRingGrowing(1)
-	for i := 0; i < x; i++ {
-		if e, a := i, g.readable; !reflect.DeepEqual(e, a) {
-			t.Fatalf("expected equal, got %#v, %#v", e, a)
-		}
-		g.WriteOne(i)
-	}
-	read := 0
-	for g.readable > 0 {
-		v, ok := g.ReadOne()
-		if !ok {
-			t.Fatal("expected true")
-		}
-		if read != v {
-			t.Fatalf("expected %#v==%#v", read, v)
-		}
-		read++
+	tests := map[string]struct {
+		ring        *TypedRingGrowing[int]
+		initialSize int
+	}{
+		"implicit-zero": {
+			ring: new(TypedRingGrowing[int]),
+		},
+		"explicit-zero": {
+			ring:        NewTypedRingGrowing[int](RingGrowingOptions{InitialSize: 0}),
+			initialSize: 0,
+		},
+		"nonzero": {
+			ring:        NewTypedRingGrowing[int](RingGrowingOptions{InitialSize: 1}),
+			initialSize: 1,
+		},
 	}
-	if x != read {
-		t.Fatalf("expected to have read %d items: %d", x, read)
+
+	for name, test := range tests {
+		t.Run(name, func(t *testing.T) {
+			initialSize := test.initialSize
+			g := test.ring
+
+			if expected, actual := 0, g.Len(); expected != actual {
+				t.Fatalf("expected Len to be %d, got %d", expected, actual)
+			}
+			if expected, actual := initialSize, g.Cap(); expected != actual {
+				t.Fatalf("expected Cap to be %d, got %d", expected, actual)
+			}
+
+			x := 10
+			for i := 0; i < x; i++ {
+				if e, a := i, g.readable; e != a {
+					t.Fatalf("expected equal, got %#v, %#v", e, a)
+				}
+				g.WriteOne(i)
+			}
+
+			if expected, actual := x, g.Len(); expected != actual {
+				t.Fatalf("expected Len to be %d, got %d", expected, actual)
+			}
+			if expected, actual := 16, g.Cap(); expected != actual {
+				t.Fatalf("expected Cap to be %d, got %d", expected, actual)
+			}
+
+			read := 0
+			for g.readable > 0 {
+				v, ok := g.ReadOne()
+				if !ok {
+					t.Fatal("expected true")
+				}
+				if read != v {
+					t.Fatalf("expected %#v==%#v", read, v)
+				}
+				read++
+			}
+			if x != read {
+				t.Fatalf("expected to have read %d items: %d", x, read)
+			}
+			if expected, actual := 0, g.Len(); expected != actual {
+				t.Fatalf("expected Len to be %d, got %d", expected, actual)
+			}
+			if expected, actual := 16, g.Cap(); expected != actual {
+				t.Fatalf("expected Cap to be %d, got %d", expected, actual)
+			}
+		})
 	}
-	if g.readable != 0 {
-		t.Fatalf("expected readable to be zero: %d", g.readable)
+
+}
+
+func TestGrowth(t *testing.T) {
+	t.Parallel()
+
+	tests := map[string]struct {
+		ring        *Ring[int]
+		initialSize int
+		normalSize  int
+	}{
+		"implicit-zero": {
+			ring: new(Ring[int]),
+		},
+		"explicit-zero": {
+			ring:        NewRing[int](RingOptions{InitialSize: 0, NormalSize: 0}),
+			initialSize: 0,
+			normalSize:  0,
+		},
+		"smaller-initial-size": {
+			ring:        NewRing[int](RingOptions{InitialSize: 1, NormalSize: 2}),
+			initialSize: 1,
+			normalSize:  2,
+		},
+		"smaller-normal-size": {
+			ring:        NewRing[int](RingOptions{InitialSize: 2, NormalSize: 1}),
+			initialSize: 2,
+			normalSize:  1,
+		},
 	}
-	if 16 != g.n {
-		t.Fatalf("expected N to be 16: %d", g.n)
+
+	for name, test := range tests {
+		t.Run(name, func(t *testing.T) {
+			initialSize := test.initialSize
+			normalSize := test.normalSize
+			g := test.ring
+
+			if expected, actual := 0, g.Len(); expected != actual {
+				t.Fatalf("expected Len to be %d, got %d", expected, actual)
+			}
+			if expected, actual := initialSize, g.Cap(); expected != actual {
+				t.Fatalf("expected Cap to be %d, got %d", expected, actual)
+			}
+
+			x := 10
+			for i := 0; i < x; i++ {
+				if e, a := i, g.growing.readable; e != a {
+					t.Fatalf("expected equal, got %#v, %#v", e, a)
+				}
+				g.WriteOne(i)
+			}
+
+			if expected, actual := x, g.Len(); expected != actual {
+				t.Fatalf("expected Len to be %d, got %d", expected, actual)
+			}
+			if expected, actual := 16, g.Cap(); expected != actual {
+				t.Fatalf("expected Cap to be %d, got %d", expected, actual)
+			}
+
+			read := 0
+			for g.growing.readable > 0 {
+				v, ok := g.ReadOne()
+				if !ok {
+					t.Fatal("expected true")
+				}
+				if read != v {
+					t.Fatalf("expected %#v==%#v", read, v)
+				}
+				read++
+			}
+			if x != read {
+				t.Fatalf("expected to have read %d items: %d", x, read)
+			}
+			if expected, actual := 0, g.Len(); expected != actual {
+				t.Fatalf("expected Len to be %d, got %d", expected, actual)
+			}
+			if expected, actual := normalSize, g.Cap(); expected != actual {
+				t.Fatalf("expected Cap to be %d, got %d", expected, actual)
+			}
+		})
 	}
 }
 
 func TestEmpty(t *testing.T) {
 	t.Parallel()
-	g := NewRingGrowing(1)
+	g := NewTypedRingGrowing[struct{}](RingGrowingOptions{InitialSize: 1})
 	_, ok := g.ReadOne()
 	if ok != false {
 		t.Fatal("expected false")