forked from google/cadvisor
-
Notifications
You must be signed in to change notification settings - Fork 1
/
queue.go
88 lines (75 loc) · 2.23 KB
/
queue.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
/*
Package queue provides a fast, ring-buffer queue based on the version suggested by Dariusz Górecki.
Using this instead of other, simpler, queue implementations (slice+append or linked list) provides
substantial memory and time benefits, and fewer GC pauses.
The queue implemented here is as fast as it is for an additional reason: it is *not* thread-safe.
*/
package queue
const minQueueLen = 16
// Queue represents a single instance of the queue data structure.
type Queue struct {
buf []interface{}
head, tail, count int
}
// New constructs and returns a new Queue.
func New() *Queue {
return &Queue{
buf: make([]interface{}, minQueueLen),
}
}
// Length returns the number of elements currently stored in the queue.
func (q *Queue) Length() int {
return q.count
}
// resizes the queue to fit exactly twice its current contents
// this can result in shrinking if the queue is less than half-full
func (q *Queue) resize() {
newBuf := make([]interface{}, q.count*2)
if q.tail > q.head {
copy(newBuf, q.buf[q.head:q.tail])
} else {
n := copy(newBuf, q.buf[q.head:])
copy(newBuf[n:], q.buf[:q.tail])
}
q.head = 0
q.tail = q.count
q.buf = newBuf
}
// Add puts an element on the end of the queue.
func (q *Queue) Add(elem interface{}) {
if q.count == len(q.buf) {
q.resize()
}
q.buf[q.tail] = elem
q.tail = (q.tail + 1) % len(q.buf)
q.count++
}
// Peek returns the element at the head of the queue. This call panics
// if the queue is empty.
func (q *Queue) Peek() interface{} {
if q.count <= 0 {
panic("queue: Peek() called on empty queue")
}
return q.buf[q.head]
}
// Get returns the element at index i in the queue. If the index is
// invalid, the call will panic.
func (q *Queue) Get(i int) interface{} {
if i < 0 || i >= q.count {
panic("queue: Get() called with index out of range")
}
return q.buf[(q.head+i)%len(q.buf)]
}
// Remove removes the element from the front of the queue. If you actually
// want the element, call Peek first. This call panics if the queue is empty.
func (q *Queue) Remove() {
if q.count <= 0 {
panic("queue: Remove() called on empty queue")
}
q.buf[q.head] = nil
q.head = (q.head + 1) % len(q.buf)
q.count--
if len(q.buf) > minQueueLen && q.count*4 == len(q.buf) {
q.resize()
}
}