go-chart/ring_buffer.go
2016-07-14 09:27:23 -07:00

218 lines
4.9 KiB
Go

package chart
import (
"fmt"
"strings"
)
const (
ringBufferMinimumGrow = 4
ringBufferShrinkThreshold = 32
ringBufferGrowFactor = 200
ringBufferDefaultCapacity = 4
)
var (
emptyArray = make([]interface{}, 0)
)
// NewRingBuffer creates a new, empty, RingBuffer.
func NewRingBuffer() *RingBuffer {
return &RingBuffer{
array: make([]interface{}, ringBufferDefaultCapacity),
head: 0,
tail: 0,
size: 0,
}
}
// NewRingBufferWithCapacity creates a new RingBuffer pre-allocated with the given capacity.
func NewRingBufferWithCapacity(capacity int) *RingBuffer {
return &RingBuffer{
array: make([]interface{}, capacity),
head: 0,
tail: 0,
size: 0,
}
}
// NewRingBufferFromSlice createsa ring buffer out of a slice.
func NewRingBufferFromSlice(values []interface{}) *RingBuffer {
return &RingBuffer{
array: values,
head: 0,
tail: len(values) - 1,
size: len(values),
}
}
// RingBuffer is a fifo buffer that is backed by a pre-allocated array, instead of allocating
// a whole new node object for each element (which saves GC churn).
// Enqueue can be O(n), Dequeue can be O(1).
type RingBuffer struct {
array []interface{}
head int
tail int
size int
}
// Len returns the length of the ring buffer (as it is currently populated).
// Actual memory footprint may be different.
func (rb *RingBuffer) Len() int {
return rb.size
}
// TotalLen returns the total size of the ring bufffer, including empty elements.
func (rb *RingBuffer) TotalLen() int {
return len(rb.array)
}
// Clear removes all objects from the RingBuffer.
func (rb *RingBuffer) Clear() {
if rb.head < rb.tail {
arrayClear(rb.array, rb.head, rb.size)
} else {
arrayClear(rb.array, rb.head, len(rb.array)-rb.head)
arrayClear(rb.array, 0, rb.tail)
}
rb.head = 0
rb.tail = 0
rb.size = 0
}
// Enqueue adds an element to the "back" of the RingBuffer.
func (rb *RingBuffer) Enqueue(object interface{}) {
if rb.size == len(rb.array) {
newCapacity := int(len(rb.array) * int(ringBufferGrowFactor/100))
if newCapacity < (len(rb.array) + ringBufferMinimumGrow) {
newCapacity = len(rb.array) + ringBufferMinimumGrow
}
rb.setCapacity(newCapacity)
}
rb.array[rb.tail] = object
rb.tail = (rb.tail + 1) % len(rb.array)
rb.size++
}
// Dequeue removes the first element from the RingBuffer.
func (rb *RingBuffer) Dequeue() interface{} {
if rb.size == 0 {
return nil
}
removed := rb.array[rb.head]
rb.head = (rb.head + 1) % len(rb.array)
rb.size--
return removed
}
// Peek returns but does not remove the first element.
func (rb *RingBuffer) Peek() interface{} {
if rb.size == 0 {
return nil
}
return rb.array[rb.head]
}
// PeekBack returns but does not remove the last element.
func (rb *RingBuffer) PeekBack() interface{} {
if rb.size == 0 {
return nil
}
if rb.tail == 0 {
return rb.array[len(rb.array)-1]
}
return rb.array[rb.tail-1]
}
func (rb *RingBuffer) setCapacity(capacity int) {
newArray := make([]interface{}, capacity)
if rb.size > 0 {
if rb.head < rb.tail {
arrayCopy(rb.array, rb.head, newArray, 0, rb.size)
} else {
arrayCopy(rb.array, rb.head, newArray, 0, len(rb.array)-rb.head)
arrayCopy(rb.array, 0, newArray, len(rb.array)-rb.head, rb.tail)
}
}
rb.array = newArray
rb.head = 0
if rb.size == capacity {
rb.tail = 0
} else {
rb.tail = rb.size
}
}
// TrimExcess resizes the buffer to better fit the contents.
func (rb *RingBuffer) TrimExcess() {
threshold := float64(len(rb.array)) * 0.9
if rb.size < int(threshold) {
rb.setCapacity(rb.size)
}
}
// AsSlice returns the ring buffer, in order, as a slice.
func (rb *RingBuffer) AsSlice() []interface{} {
newArray := make([]interface{}, rb.size)
if rb.size == 0 {
return newArray
}
if rb.head < rb.tail {
arrayCopy(rb.array, rb.head, newArray, 0, rb.size)
} else {
arrayCopy(rb.array, rb.head, newArray, 0, len(rb.array)-rb.head)
arrayCopy(rb.array, 0, newArray, len(rb.array)-rb.head, rb.tail)
}
return newArray
}
// Each calls the consumer for each element in the buffer.
func (rb *RingBuffer) Each(consumer func(value interface{})) {
if rb.size == 0 {
return
}
if rb.head < rb.tail {
for cursor := rb.head; cursor < rb.tail; cursor++ {
consumer(rb.array[cursor])
}
} else {
for cursor := rb.head; cursor < len(rb.array); cursor++ {
consumer(rb.array[cursor])
}
for cursor := 0; cursor < rb.tail; cursor++ {
consumer(rb.array[cursor])
}
}
}
func (rb *RingBuffer) String() string {
var values []string
for _, elem := range rb.AsSlice() {
values = append(values, fmt.Sprintf("%v", elem))
}
return strings.Join(values, " <= ")
}
func arrayClear(source []interface{}, index, length int) {
for x := 0; x < length; x++ {
absoluteIndex := x + index
source[absoluteIndex] = nil
}
}
func arrayCopy(source []interface{}, sourceIndex int, destination []interface{}, destinationIndex, length int) {
for x := 0; x < length; x++ {
from := sourceIndex + x
to := destinationIndex + x
destination[to] = source[from]
}
}