mirror of
https://github.com/jech/galene.git
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546 lines
12 KiB
Go
546 lines
12 KiB
Go
// Package packetcache implement a packet cache that maintains a history
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// of recently seen packets, the last keyframe, and a number of statistics
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// that are needed for sending receiver reports.
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package packetcache
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import (
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"math/bits"
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"sync"
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)
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// The maximum size of packets stored in the cache. Chosen to be
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// a multiple of 8.
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const BufSize = 1504
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// The maximum number of packets that constitute a keyframe.
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const maxFrame = 1024
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// entry represents a cached packet.
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type entry struct {
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seqno uint16
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lengthAndMarker uint16 // 1 bit of marker, 15 bits of length
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timestamp uint32
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buf [BufSize]byte
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}
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func (e *entry) length() uint16 {
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return e.lengthAndMarker & 0x7FFF
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}
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func (e *entry) marker() bool {
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return (e.lengthAndMarker & 0x8000) != 0
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}
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// bitmap keeps track of recent loss history
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type bitmap struct {
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valid bool
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first uint16
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bitmap uint32
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}
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// frame is used for storing the last keyframe
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type frame struct {
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timestamp uint32
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complete bool
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entries []entry
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}
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type Cache struct {
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mu sync.Mutex
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//stats
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last uint16
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cycle uint16
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lastValid bool
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expected uint32
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lost uint32
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totalLost uint32
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// bitmap
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bitmap bitmap
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// buffered keyframe
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keyframe frame
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// the actual cache
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tail uint16
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entries []entry
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}
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// New creates a cache with the given capacity.
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func New(capacity int) *Cache {
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if capacity > int(^uint16(0)) {
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return nil
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}
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return &Cache{
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entries: make([]entry, capacity),
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}
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}
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// compare performs comparison modulo 2^16.
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func compare(s1, s2 uint16) int {
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if s1 == s2 {
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return 0
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}
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if ((s2 - s1) & 0x8000) != 0 {
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return 1
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}
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return -1
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}
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// seqnoInvalid returns true if seqno is unreasonably far in the past
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func seqnoInvalid(seqno, reference uint16) bool {
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if compare(reference, seqno) < 0 {
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return false
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}
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if reference-seqno > 0x100 {
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return true
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}
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return false
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}
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// set sets a bit in the bitmap, shifting if necessary
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func (bitmap *bitmap) set(seqno uint16) {
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if !bitmap.valid || seqnoInvalid(seqno, bitmap.first) {
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bitmap.first = seqno
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bitmap.bitmap = 1
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bitmap.valid = true
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return
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}
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if compare(bitmap.first, seqno) > 0 {
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return
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}
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if seqno-bitmap.first >= 32 {
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shift := seqno - bitmap.first - 31
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bitmap.bitmap >>= shift
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bitmap.first += shift
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}
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if (bitmap.bitmap & 1) == 1 {
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ones := bits.TrailingZeros32(^bitmap.bitmap)
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bitmap.bitmap >>= ones
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bitmap.first += uint16(ones)
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}
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bitmap.bitmap |= (1 << uint16(seqno-bitmap.first))
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return
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}
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// BitmapGet shifts up to 17 bits out of the bitmap. It returns a boolean
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// indicating if any were 0, the index of the first 0 bit, and a bitmap
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// indicating any 0 bits after the first one.
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func (cache *Cache) BitmapGet(next uint16) (bool, uint16, uint16) {
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cache.mu.Lock()
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defer cache.mu.Unlock()
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return cache.bitmap.get(next)
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}
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func (bitmap *bitmap) get(next uint16) (bool, uint16, uint16) {
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first := bitmap.first
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if compare(first, next) >= 0 {
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return false, first, 0
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}
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count := next - first
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if count > 17 {
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count = 17
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}
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bm := (^bitmap.bitmap) & ^((^uint32(0)) << count)
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bitmap.bitmap >>= count
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bitmap.first += count
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if bm == 0 {
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return false, first, 0
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}
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if (bm & 1) == 0 {
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count := bits.TrailingZeros32(bm)
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bm >>= count
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first += uint16(count)
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}
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return true, first, uint16(bm >> 1)
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}
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// insert inserts a packet into a frame.
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func (frame *frame) insert(seqno uint16, timestamp uint32, marker bool, data []byte) bool {
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n := len(frame.entries)
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i := 0
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if n == 0 || seqno > frame.entries[n-1].seqno {
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// fast path
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i = n
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} else {
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for i < n {
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if frame.entries[i].seqno >= seqno {
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break
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}
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i++
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}
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if i < n && frame.entries[i].seqno == seqno {
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// duplicate
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return false
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}
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}
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if n >= maxFrame {
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// overflow
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return false
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}
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lam := uint16(len(data))
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if marker {
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lam |= 0x8000
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}
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e := entry{
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seqno: seqno,
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lengthAndMarker: lam,
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timestamp: timestamp,
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}
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copy(e.buf[:], data)
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if i >= n {
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frame.entries = append(frame.entries, e)
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return true
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}
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frame.entries = append(frame.entries, entry{})
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copy(frame.entries[i+1:], frame.entries[i:])
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frame.entries[i] = e
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return true
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}
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// store checks whether a packet is part of the current keyframe and, if
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// so, inserts it.
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func (frame *frame) store(seqno uint16, timestamp uint32, first bool, marker bool, data []byte) bool {
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if first {
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if frame.timestamp != timestamp {
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frame.timestamp = timestamp
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frame.complete = false
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frame.entries = frame.entries[:0]
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}
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} else if len(frame.entries) > 0 {
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if frame.timestamp != timestamp {
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delta := seqno - frame.entries[0].seqno
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if (delta&0x8000) == 0 && delta > 0x4000 {
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frame.complete = false
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frame.entries = frame.entries[:0]
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}
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return false
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}
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} else {
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return false
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}
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done := frame.insert(seqno, timestamp, marker, data)
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if done && !frame.complete {
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marker := false
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fst := frame.entries[0].seqno
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for i := 1; i < len(frame.entries); i++ {
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if frame.entries[i].seqno != fst+uint16(i) {
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return done
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}
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if frame.entries[i].marker() {
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marker = true
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}
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}
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if marker {
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frame.complete = true
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}
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}
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return done
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}
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// Store stores a packet in the cache. It returns the first seqno in the
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// bitmap, and the index at which the packet was stored.
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func (cache *Cache) Store(seqno uint16, timestamp uint32, keyframe bool, marker bool, buf []byte) (uint16, uint16) {
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cache.mu.Lock()
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defer cache.mu.Unlock()
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if !cache.lastValid || seqnoInvalid(seqno, cache.last) {
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cache.last = seqno
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cache.lastValid = true
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cache.expected++
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} else {
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if compare(cache.last, seqno) <= 0 {
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cache.expected += uint32(seqno - cache.last)
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cache.lost += uint32(seqno - cache.last - 1)
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if seqno < cache.last {
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cache.cycle++
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}
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cache.last = seqno
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} else {
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if cache.lost > 0 {
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cache.lost--
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}
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}
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}
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cache.bitmap.set(seqno)
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done := cache.keyframe.store(seqno, timestamp, keyframe, marker, buf)
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if done && !cache.keyframe.complete {
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completeKeyframe(cache)
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}
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i := cache.tail
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cache.entries[i].seqno = seqno
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copy(cache.entries[i].buf[:], buf)
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lam := uint16(len(buf))
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if marker {
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lam |= 0x8000
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}
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cache.entries[i].lengthAndMarker = lam
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cache.entries[i].timestamp = timestamp
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cache.tail = (i + 1) % uint16(len(cache.entries))
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return cache.bitmap.first, i
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}
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// completeKeyFrame attempts to complete the current keyframe.
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func completeKeyframe(cache *Cache) {
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l := len(cache.keyframe.entries)
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if l == 0 {
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return
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}
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first := cache.keyframe.entries[0].seqno
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last := cache.keyframe.entries[l-1].seqno
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count := (last - first) // may wrap around
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if count > 0x4000 {
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// this shouldn't happen
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return
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}
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var buf []byte
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if count > 1 {
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if buf == nil {
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buf = make([]byte, BufSize)
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}
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for i := uint16(1); i < count; i++ {
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n, ts, marker := get(first+i, cache.entries, buf)
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if n > 0 {
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cache.keyframe.store(
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first+i, ts, false, marker, buf,
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)
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}
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}
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}
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if !cache.keyframe.complete {
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// Try to find packets after the last one.
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for {
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l := len(cache.keyframe.entries)
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if cache.keyframe.entries[l-1].marker() {
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break
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}
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if buf == nil {
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buf = make([]byte, BufSize)
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}
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seqno := cache.keyframe.entries[l-1].seqno + 1
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n, ts, marker := get(seqno, cache.entries, buf)
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if n <= 0 {
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break
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}
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done := cache.keyframe.store(
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seqno, ts, false, marker, buf,
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)
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if !done || marker {
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break
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}
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}
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}
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}
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// Expect records that we expect n packets. It is used for loss statistics.
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func (cache *Cache) Expect(n int) {
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if n <= 0 {
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return
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}
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cache.mu.Lock()
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defer cache.mu.Unlock()
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cache.expected += uint32(n)
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}
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// get retrieves a packet from a slice of entries.
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func get(seqno uint16, entries []entry, result []byte) (uint16, uint32, bool) {
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for i := range entries {
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if entries[i].lengthAndMarker == 0 || entries[i].seqno != seqno {
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continue
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}
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var n uint16
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if len(result) > 0 {
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n = uint16(copy(
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result[:entries[i].length()],
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entries[i].buf[:]))
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} else {
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n = entries[i].length()
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}
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return n, entries[i].timestamp, entries[i].marker()
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}
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return 0, 0, false
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}
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// Get retrieves a packet from the cache, returns the number of bytes
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// copied. If result is of length 0, returns the size of the packet.
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func (cache *Cache) Get(seqno uint16, result []byte) uint16 {
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cache.mu.Lock()
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defer cache.mu.Unlock()
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n, _, _ := get(seqno, cache.keyframe.entries, result)
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if n > 0 {
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return n
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}
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n, _, _ = get(seqno, cache.entries, result)
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if n > 0 {
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return n
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}
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return 0
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}
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func (cache *Cache) Last() (bool, uint16, uint32) {
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cache.mu.Lock()
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defer cache.mu.Unlock()
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if !cache.lastValid {
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return false, 0, 0
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}
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len, ts, _ := get(cache.last, cache.entries, nil)
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if len == 0 {
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return false, 0, 0
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}
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return true, cache.last, ts
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}
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// GetAt retrieves a packet from the cache assuming it is at the given index.
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func (cache *Cache) GetAt(seqno uint16, index uint16, result []byte) uint16 {
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cache.mu.Lock()
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defer cache.mu.Unlock()
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if int(index) > len(cache.entries) {
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return 0
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}
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if cache.entries[index].seqno != seqno {
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return 0
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}
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return uint16(copy(
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result[:cache.entries[index].length()],
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cache.entries[index].buf[:]),
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)
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}
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// Keyframe returns the last buffered keyframe. It returns the frame's
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// timestamp and a boolean indicating if the frame is complete.
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func (cache *Cache) Keyframe() (uint32, bool, []uint16) {
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cache.mu.Lock()
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defer cache.mu.Unlock()
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if len(cache.keyframe.entries) == 0 {
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return 0, false, nil
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}
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seqnos := make([]uint16, len(cache.keyframe.entries))
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for i := range cache.keyframe.entries {
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seqnos[i] = cache.keyframe.entries[i].seqno
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}
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return cache.keyframe.timestamp, cache.keyframe.complete, seqnos
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}
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func (cache *Cache) KeyframeSeqno() (bool, uint16, uint32) {
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cache.mu.Lock()
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defer cache.mu.Unlock()
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if len(cache.keyframe.entries) == 0 {
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return false, 0, 0
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}
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return true, cache.keyframe.entries[0].seqno, cache.keyframe.timestamp
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}
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func (cache *Cache) resize(capacity int) {
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if len(cache.entries) == capacity {
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return
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}
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entries := make([]entry, capacity)
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if capacity > len(cache.entries) {
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copy(entries, cache.entries[:cache.tail])
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copy(entries[int(cache.tail)+capacity-len(cache.entries):],
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cache.entries[cache.tail:])
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} else if capacity > int(cache.tail) {
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copy(entries, cache.entries[:cache.tail])
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copy(entries[cache.tail:],
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cache.entries[int(cache.tail)+
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len(cache.entries)-capacity:])
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} else {
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// too bad, invalidate all indices
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copy(entries,
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cache.entries[int(cache.tail)-capacity:cache.tail])
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cache.tail = 0
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}
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cache.entries = entries
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}
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// Resize resizes the cache to the given capacity. This might invalidate
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// indices of recently stored packets.
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func (cache *Cache) Resize(capacity int) {
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cache.mu.Lock()
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defer cache.mu.Unlock()
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cache.resize(capacity)
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}
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// ResizeCond is like Resize, but avoids invalidating recent indices.
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func (cache *Cache) ResizeCond(capacity int) bool {
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cache.mu.Lock()
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defer cache.mu.Unlock()
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current := len(cache.entries)
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if current >= capacity*3/4 && current < capacity*2 {
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return false
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}
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if capacity < current {
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if int(cache.tail) > capacity {
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// this would invalidate too many indices
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return false
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}
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}
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cache.resize(capacity)
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return true
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}
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|
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// GetStats returns statistics about received packets. If reset is true,
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// the statistics are reset.
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func (cache *Cache) GetStats(reset bool) (uint32, uint32, uint32, uint32) {
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cache.mu.Lock()
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defer cache.mu.Unlock()
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expected := cache.expected
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lost := cache.lost
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totalLost := cache.totalLost + cache.lost
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eseqno := uint32(cache.cycle)<<16 | uint32(cache.last)
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if reset {
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cache.expected = 0
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cache.totalLost += cache.lost
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cache.lost = 0
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}
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return expected, lost, totalLost, eseqno
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}
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// ToBitmap takes a non-empty sorted list of seqnos, and computes a bitmap
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// covering a prefix of the list. It returns the part of the list that
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// couldn't be covered.
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func ToBitmap(seqnos []uint16) (first uint16, bitmap uint16, remain []uint16) {
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first = seqnos[0]
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bitmap = uint16(0)
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remain = seqnos[1:]
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for len(remain) > 0 {
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delta := remain[0] - first - 1
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if delta >= 16 {
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break
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}
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bitmap = bitmap | (1 << delta)
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remain = remain[1:]
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}
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return
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}
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