a223e4eedb
This commit introduces a fixed size circular buffer which stores elements in a fixed size underlying array, wrapping to overwrite items when the buffer gets full.
117 lines
3.4 KiB
Go
117 lines
3.4 KiB
Go
package queue
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import (
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"errors"
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)
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// errInvalidSize is returned when an invalid size for a buffer is provided.
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var errInvalidSize = errors.New("buffer size must be > 0")
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// CircularBuffer is a buffer which retains a set of values in memory, and
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// overwrites the oldest item in the buffer when a new item needs to be
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// written.
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type CircularBuffer struct {
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// total is the total number of items that have been added to the
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// buffer.
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total int
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// items is the set of buffered items.
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items []interface{}
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}
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// NewCircularBuffer returns a new circular buffer with the size provided. It
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// will fail if a zero or negative size parameter is provided.
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func NewCircularBuffer(size int) (*CircularBuffer, error) {
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if size <= 0 {
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return nil, errInvalidSize
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}
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return &CircularBuffer{
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total: 0,
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// Create a slice with length and capacity equal to the size of
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// the buffer so that we do not need to resize the underlying
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// array when we add items.
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items: make([]interface{}, size),
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}, nil
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}
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// index returns the index that should be written to next.
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func (c *CircularBuffer) index() int {
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return c.total % len(c.items)
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}
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// Add adds an item to the buffer, overwriting the oldest item if the buffer
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// is full.
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func (c *CircularBuffer) Add(item interface{}) {
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// Set the item in the next free index in the items array.
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c.items[c.index()] = item
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// Increment the total number of items that we have stored.
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c.total++
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}
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// List returns a copy of the items in the buffer ordered from the oldest to
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// newest item.
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func (c *CircularBuffer) List() []interface{} {
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size := cap(c.items)
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index := c.index()
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switch {
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// If no items have been stored yet, we can just return a nil list.
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case c.total == 0:
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return nil
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// If we have added fewer items than the buffer size, we can simply
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// return the total number of items from the beginning of the list
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// to the index. This special case is added because the oldest item
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// is at the beginning of the underlying array, not at the index when
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// we have not filled the array yet.
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case c.total < size:
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resp := make([]interface{}, c.total)
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copy(resp, c.items[:c.index()])
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return resp
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}
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resp := make([]interface{}, size)
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// Get the items in the underlying array from index to end, the first
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// item in this slice will be the oldest item in the list.
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firstHalf := c.items[index:]
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// Copy the first set into our response slice from index 0, so that
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// the response returned is from oldest to newest.
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copy(resp, firstHalf)
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// Get the items in the underlying array from beginning until the write
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// index, the last item in this slice will be the newest item in the
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// list.
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secondHalf := c.items[:index]
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// Copy the second set of items into the response slice offset by the
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// length of the first set of items so that we return a response which
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// is ordered from oldest to newest entry.
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copy(resp[len(firstHalf):], secondHalf)
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return resp
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}
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// Total returns the total number of items that have been added to the buffer.
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func (c *CircularBuffer) Total() int {
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return c.total
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}
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// Latest returns the item that was most recently added to the buffer.
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func (c *CircularBuffer) Latest() interface{} {
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// If no items have been added yet, return nil.
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if c.total == 0 {
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return nil
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}
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// The latest item is one before our total, mod by length.
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latest := (c.total - 1) % len(c.items)
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// Return the latest item added.
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return c.items[latest]
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}
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