lnd.xprv/queue/circular_buf.go

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package queue
import (
"errors"
)
// errInvalidSize is returned when an invalid size for a buffer is provided.
var errInvalidSize = errors.New("buffer size must be > 0")
// CircularBuffer is a buffer which retains a set of values in memory, and
// overwrites the oldest item in the buffer when a new item needs to be
// written.
type CircularBuffer struct {
// total is the total number of items that have been added to the
// buffer.
total int
// items is the set of buffered items.
items []interface{}
}
// NewCircularBuffer returns a new circular buffer with the size provided. It
// will fail if a zero or negative size parameter is provided.
func NewCircularBuffer(size int) (*CircularBuffer, error) {
if size <= 0 {
return nil, errInvalidSize
}
return &CircularBuffer{
total: 0,
// Create a slice with length and capacity equal to the size of
// the buffer so that we do not need to resize the underlying
// array when we add items.
items: make([]interface{}, size),
}, nil
}
// index returns the index that should be written to next.
func (c *CircularBuffer) index() int {
return c.total % len(c.items)
}
// Add adds an item to the buffer, overwriting the oldest item if the buffer
// is full.
func (c *CircularBuffer) Add(item interface{}) {
// Set the item in the next free index in the items array.
c.items[c.index()] = item
// Increment the total number of items that we have stored.
c.total++
}
// List returns a copy of the items in the buffer ordered from the oldest to
// newest item.
func (c *CircularBuffer) List() []interface{} {
size := cap(c.items)
index := c.index()
switch {
// If no items have been stored yet, we can just return a nil list.
case c.total == 0:
return nil
// If we have added fewer items than the buffer size, we can simply
// return the total number of items from the beginning of the list
// to the index. This special case is added because the oldest item
// is at the beginning of the underlying array, not at the index when
// we have not filled the array yet.
case c.total < size:
resp := make([]interface{}, c.total)
copy(resp, c.items[:c.index()])
return resp
}
resp := make([]interface{}, size)
// Get the items in the underlying array from index to end, the first
// item in this slice will be the oldest item in the list.
firstHalf := c.items[index:]
// Copy the first set into our response slice from index 0, so that
// the response returned is from oldest to newest.
copy(resp, firstHalf)
// Get the items in the underlying array from beginning until the write
// index, the last item in this slice will be the newest item in the
// list.
secondHalf := c.items[:index]
// Copy the second set of items into the response slice offset by the
// length of the first set of items so that we return a response which
// is ordered from oldest to newest entry.
copy(resp[len(firstHalf):], secondHalf)
return resp
}
// Total returns the total number of items that have been added to the buffer.
func (c *CircularBuffer) Total() int {
return c.total
}
// Latest returns the item that was most recently added to the buffer.
func (c *CircularBuffer) Latest() interface{} {
// If no items have been added yet, return nil.
if c.total == 0 {
return nil
}
// The latest item is one before our total, mod by length.
latest := (c.total - 1) % len(c.items)
// Return the latest item added.
return c.items[latest]
}