Update BBR congestion control

congestion_meta2/packet_number_indexed_queue.go

@@ -0,0 +1,199 @@
+package congestion
+
+import (
+	"github.com/sagernet/quic-go/congestion"
+)
+
+// packetNumberIndexedQueue is a queue of mostly continuous numbered entries
+// which supports the following operations:
+// - adding elements to the end of the queue, or at some point past the end
+// - removing elements in any order
+// - retrieving elements
+// If all elements are inserted in order, all of the operations above are
+// amortized O(1) time.
+//
+// Internally, the data structure is a deque where each element is marked as
+// present or not.  The deque starts at the lowest present index.  Whenever an
+// element is removed, it's marked as not present, and the front of the deque is
+// cleared of elements that are not present.
+//
+// The tail of the queue is not cleared due to the assumption of entries being
+// inserted in order, though removing all elements of the queue will return it
+// to its initial state.
+//
+// Note that this data structure is inherently hazardous, since an addition of
+// just two entries will cause it to consume all of the memory available.
+// Because of that, it is not a general-purpose container and should not be used
+// as one.
+
+type entryWrapper[T any] struct {
+	present bool
+	entry   T
+}
+
+type packetNumberIndexedQueue[T any] struct {
+	entries                RingBuffer[entryWrapper[T]]
+	numberOfPresentEntries int
+	firstPacket            congestion.PacketNumber
+}
+
+func newPacketNumberIndexedQueue[T any](size int) *packetNumberIndexedQueue[T] {
+	q := &packetNumberIndexedQueue[T]{
+		firstPacket: invalidPacketNumber,
+	}
+
+	q.entries.Init(size)
+
+	return q
+}
+
+// Emplace inserts data associated |packet_number| into (or past) the end of the
+// queue, filling up the missing intermediate entries as necessary.  Returns
+// true if the element has been inserted successfully, false if it was already
+// in the queue or inserted out of order.
+func (p *packetNumberIndexedQueue[T]) Emplace(packetNumber congestion.PacketNumber, entry *T) bool {
+	if packetNumber == invalidPacketNumber || entry == nil {
+		return false
+	}
+
+	if p.IsEmpty() {
+		p.entries.PushBack(entryWrapper[T]{
+			present: true,
+			entry:   *entry,
+		})
+		p.numberOfPresentEntries = 1
+		p.firstPacket = packetNumber
+		return true
+	}
+
+	// Do not allow insertion out-of-order.
+	if packetNumber <= p.LastPacket() {
+		return false
+	}
+
+	// Handle potentially missing elements.
+	offset := int(packetNumber - p.FirstPacket())
+	if gap := offset - p.entries.Len(); gap > 0 {
+		for i := 0; i < gap; i++ {
+			p.entries.PushBack(entryWrapper[T]{})
+		}
+	}
+
+	p.entries.PushBack(entryWrapper[T]{
+		present: true,
+		entry:   *entry,
+	})
+	p.numberOfPresentEntries++
+	return true
+}
+
+// GetEntry Retrieve the entry associated with the packet number.  Returns the pointer
+// to the entry in case of success, or nullptr if the entry does not exist.
+func (p *packetNumberIndexedQueue[T]) GetEntry(packetNumber congestion.PacketNumber) *T {
+	ew := p.getEntryWraper(packetNumber)
+	if ew == nil {
+		return nil
+	}
+
+	return &ew.entry
+}
+
+// Remove, Same as above, but if an entry is present in the queue, also call f(entry)
+// before removing it.
+func (p *packetNumberIndexedQueue[T]) Remove(packetNumber congestion.PacketNumber, f func(T)) bool {
+	ew := p.getEntryWraper(packetNumber)
+	if ew == nil {
+		return false
+	}
+	if f != nil {
+		f(ew.entry)
+	}
+	ew.present = false
+	p.numberOfPresentEntries--
+
+	if packetNumber == p.FirstPacket() {
+		p.clearup()
+	}
+
+	return true
+}
+
+// RemoveUpTo, but not including |packet_number|.
+// Unused slots in the front are also removed, which means when the function
+// returns, |first_packet()| can be larger than |packet_number|.
+func (p *packetNumberIndexedQueue[T]) RemoveUpTo(packetNumber congestion.PacketNumber) {
+	for !p.entries.Empty() &&
+		p.firstPacket != invalidPacketNumber &&
+		p.firstPacket < packetNumber {
+		if p.entries.Front().present {
+			p.numberOfPresentEntries--
+		}
+		p.entries.PopFront()
+		p.firstPacket++
+	}
+	p.clearup()
+
+	return
+}
+
+// IsEmpty return if queue is empty.
+func (p *packetNumberIndexedQueue[T]) IsEmpty() bool {
+	return p.numberOfPresentEntries == 0
+}
+
+// NumberOfPresentEntries returns the number of entries in the queue.
+func (p *packetNumberIndexedQueue[T]) NumberOfPresentEntries() int {
+	return p.numberOfPresentEntries
+}
+
+// EntrySlotsUsed returns the number of entries allocated in the underlying deque.  This is
+// proportional to the memory usage of the queue.
+func (p *packetNumberIndexedQueue[T]) EntrySlotsUsed() int {
+	return p.entries.Len()
+}
+
+// LastPacket returns packet number of the first entry in the queue.
+func (p *packetNumberIndexedQueue[T]) FirstPacket() (packetNumber congestion.PacketNumber) {
+	return p.firstPacket
+}
+
+// LastPacket returns packet number of the last entry ever inserted in the queue.  Note that the
+// entry in question may have already been removed.  Zero if the queue is
+// empty.
+func (p *packetNumberIndexedQueue[T]) LastPacket() (packetNumber congestion.PacketNumber) {
+	if p.IsEmpty() {
+		return invalidPacketNumber
+	}
+
+	return p.firstPacket + congestion.PacketNumber(p.entries.Len()-1)
+}
+
+func (p *packetNumberIndexedQueue[T]) clearup() {
+	for !p.entries.Empty() && !p.entries.Front().present {
+		p.entries.PopFront()
+		p.firstPacket++
+	}
+	if p.entries.Empty() {
+		p.firstPacket = invalidPacketNumber
+	}
+}
+
+func (p *packetNumberIndexedQueue[T]) getEntryWraper(packetNumber congestion.PacketNumber) *entryWrapper[T] {
+	if packetNumber == invalidPacketNumber ||
+		p.IsEmpty() ||
+		packetNumber < p.firstPacket {
+		return nil
+	}
+
+	offset := int(packetNumber - p.firstPacket)
+	if offset >= p.entries.Len() {
+		return nil
+	}
+
+	ew := p.entries.Offset(offset)
+	if ew == nil || !ew.present {
+		return nil
+	}
+
+	return ew
+}