ceremonyclient/pebble/internal/ackseq/ackseq.go

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2024-01-03 07:31:42 +00:00
// Copyright 2019 The LevelDB-Go and Pebble Authors. All rights reserved. Use
// of this source code is governed by a BSD-style license that can be found in
// the LICENSE file.
package ackseq
import (
"sync"
"sync/atomic"
"github.com/cockroachdb/errors"
)
const (
// The window size constants. These values specify a window that can hold ~1m
// pending unacknowledged sequence numbers using 128 KB of memory.
windowSize = 1 << 20
windowMask = windowSize - 1
windowBytes = (windowSize + 7) / 8
)
// S keeps track of the largest sequence number such that all sequence numbers
// in the range [0,v) have been acknowledged.
type S struct {
next atomic.Uint64
mu struct {
sync.Mutex
base uint64
window [windowBytes]uint8
}
}
// New creates a new acknowledged sequence tracker with the specified base
// sequence number. All of the sequence numbers in the range [0,base) are
// considered acknowledged. Next() will return base upon first call.
func New(base uint64) *S {
s := &S{}
s.next.Store(base)
s.mu.base = base
return s
}
// Next returns the next sequence number to use.
func (s *S) Next() uint64 {
return s.next.Add(1) - 1
}
// Ack acknowledges the specified seqNum, adjusting base as necessary,
// returning the number of newly acknowledged sequence numbers.
func (s *S) Ack(seqNum uint64) (int, error) {
s.mu.Lock()
if s.getLocked(seqNum) {
defer s.mu.Unlock()
return 0, errors.Errorf(
"pending acks exceeds window size: %d has been acked, but %d has not",
errors.Safe(seqNum), errors.Safe(s.mu.base))
}
var count int
s.setLocked(seqNum)
for s.getLocked(s.mu.base) {
s.clearLocked(s.mu.base)
s.mu.base++
count++
}
s.mu.Unlock()
return count, nil
}
func (s *S) getLocked(seqNum uint64) bool {
bit := seqNum & windowMask
return (s.mu.window[bit/8] & (1 << (bit % 8))) != 0
}
func (s *S) setLocked(seqNum uint64) {
bit := seqNum & windowMask
s.mu.window[bit/8] |= (1 << (bit % 8))
}
func (s *S) clearLocked(seqNum uint64) {
bit := seqNum & windowMask
s.mu.window[bit/8] &^= (1 << (bit % 8))
}