lotus/chain/sub/ratelimit/queue.go

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package ratelimit
import "errors"
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var ErrRateLimitExceeded = errors.New("rate limit exceeded")
type queue struct {
buf []int64
count int
head int
tail int
}
// cap returns the queue capacity
func (q *queue) cap() int {
return len(q.buf)
}
// len returns the number of items in the queue
func (q *queue) len() int {
return q.count
}
// push adds an element to the end of the queue.
func (q *queue) push(elem int64) error {
if q.count == len(q.buf) {
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return ErrRateLimitExceeded
}
q.buf[q.tail] = elem
// Calculate new tail position.
q.tail = q.next(q.tail)
q.count++
return nil
}
// pop removes and returns the element from the front of the queue.
func (q *queue) pop() int64 {
if q.count <= 0 {
panic("pop from empty queue")
}
ret := q.buf[q.head]
// Calculate new head position.
q.head = q.next(q.head)
q.count--
return ret
}
// front returns the element at the front of the queue. This is the element
// that would be returned by pop(). This call panics if the queue is empty.
func (q *queue) front() int64 {
if q.count <= 0 {
panic("front() called when empty")
}
return q.buf[q.head]
}
// back returns the element at the back of the queue. This call panics if the
// queue is empty.
func (q *queue) back() int64 {
if q.count <= 0 {
panic("back() called when empty")
}
return q.buf[q.prev(q.tail)]
}
// prev returns the previous buffer position wrapping around buffer.
func (q *queue) prev(i int) int {
if i == 0 {
return len(q.buf) - 1
}
return (i - 1) % len(q.buf)
}
// next returns the next buffer position wrapping around buffer.
func (q *queue) next(i int) int {
return (i + 1) % len(q.buf)
}
// truncate pops values that are less than or equal the specified threshold.
func (q *queue) truncate(threshold int64) {
for q.count != 0 && q.buf[q.head] <= threshold {
// pop() without returning a value
q.head = q.next(q.head)
q.count--
}
}