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// Copyright 2023 The Go 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 http2
import (
"fmt"
"math"
)
type roundRobinWriteScheduler struct {
// control contains control frames (SETTINGS, PING, etc.).
control writeQueue
// streams maps stream ID to a queue.
streams map[uint32]*writeQueue
// stream queues are stored in a circular linked list.
// head is the next stream to write, or nil if there are no streams open.
head *writeQueue
// pool of empty queues for reuse.
queuePool writeQueuePool
}
// newRoundRobinWriteScheduler constructs a new write scheduler.
// The round robin scheduler priorizes control frames
// like SETTINGS and PING over DATA frames.
// When there are no control frames to send, it performs a round-robin
// selection from the ready streams.
func newRoundRobinWriteScheduler() WriteScheduler {
ws := &roundRobinWriteScheduler{
streams: make(map[uint32]*writeQueue),
}
return ws
}
func (ws *roundRobinWriteScheduler) OpenStream(streamID uint32, options OpenStreamOptions) {
if ws.streams[streamID] != nil {
panic(fmt.Errorf("stream %d already opened", streamID))
}
q := ws.queuePool.get()
ws.streams[streamID] = q
if ws.head == nil {
ws.head = q
q.next = q
q.prev = q
} else {
// Queues are stored in a ring.
// Insert the new stream before ws.head, putting it at the end of the list.
q.prev = ws.head.prev
q.next = ws.head
q.prev.next = q
q.next.prev = q
}
}
func (ws *roundRobinWriteScheduler) CloseStream(streamID uint32) {
q := ws.streams[streamID]
if q == nil {
return
}
if q.next == q {
// This was the only open stream.
ws.head = nil
} else {
q.prev.next = q.next
q.next.prev = q.prev
if ws.head == q {
ws.head = q.next
}
}
delete(ws.streams, streamID)
ws.queuePool.put(q)
}
func (ws *roundRobinWriteScheduler) AdjustStream(streamID uint32, priority PriorityParam) {}
func (ws *roundRobinWriteScheduler) Push(wr FrameWriteRequest) {
if wr.isControl() {
ws.control.push(wr)
return
}
q := ws.streams[wr.StreamID()]
if q == nil {
// This is a closed stream.
// wr should not be a HEADERS or DATA frame.
// We push the request onto the control queue.
if wr.DataSize() > 0 {
panic("add DATA on non-open stream")
}
ws.control.push(wr)
return
}
q.push(wr)
}
func (ws *roundRobinWriteScheduler) Pop() (FrameWriteRequest, bool) {
// Control and RST_STREAM frames first.
if !ws.control.empty() {
return ws.control.shift(), true
}
if ws.head == nil {
return FrameWriteRequest{}, false
}
q := ws.head
for {
if wr, ok := q.consume(math.MaxInt32); ok {
ws.head = q.next
return wr, true
}
q = q.next
if q == ws.head {
break
}
}
return FrameWriteRequest{}, false
}
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