1// Copyright 2014 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package http2
6
7import "math"
8
9// NewRandomWriteScheduler constructs a WriteScheduler that ignores HTTP/2
10// priorities. Control frames like SETTINGS and PING are written before DATA
11// frames, but if no control frames are queued and multiple streams have queued
12// HEADERS or DATA frames, Pop selects a ready stream arbitrarily.
13func NewRandomWriteScheduler() WriteScheduler {
14	return &randomWriteScheduler{sq: make(map[uint32]*writeQueue)}
15}
16
17type randomWriteScheduler struct {
18	// zero are frames not associated with a specific stream.
19	zero writeQueue
20
21	// sq contains the stream-specific queues, keyed by stream ID.
22	// When a stream is idle, closed, or emptied, it's deleted
23	// from the map.
24	sq map[uint32]*writeQueue
25
26	// pool of empty queues for reuse.
27	queuePool writeQueuePool
28}
29
30func (ws *randomWriteScheduler) OpenStream(streamID uint32, options OpenStreamOptions) {
31	// no-op: idle streams are not tracked
32}
33
34func (ws *randomWriteScheduler) CloseStream(streamID uint32) {
35	q, ok := ws.sq[streamID]
36	if !ok {
37		return
38	}
39	delete(ws.sq, streamID)
40	ws.queuePool.put(q)
41}
42
43func (ws *randomWriteScheduler) AdjustStream(streamID uint32, priority PriorityParam) {
44	// no-op: priorities are ignored
45}
46
47func (ws *randomWriteScheduler) Push(wr FrameWriteRequest) {
48	id := wr.StreamID()
49	if id == 0 {
50		ws.zero.push(wr)
51		return
52	}
53	q, ok := ws.sq[id]
54	if !ok {
55		q = ws.queuePool.get()
56		ws.sq[id] = q
57	}
58	q.push(wr)
59}
60
61func (ws *randomWriteScheduler) Pop() (FrameWriteRequest, bool) {
62	// Control frames first.
63	if !ws.zero.empty() {
64		return ws.zero.shift(), true
65	}
66	// Iterate over all non-idle streams until finding one that can be consumed.
67	for streamID, q := range ws.sq {
68		if wr, ok := q.consume(math.MaxInt32); ok {
69			if q.empty() {
70				delete(ws.sq, streamID)
71				ws.queuePool.put(q)
72			}
73			return wr, true
74		}
75	}
76	return FrameWriteRequest{}, false
77}
78