http2: interface to support pluggable schedulers

This adds an interface to support pluggable schedulers. The interface
is defined in writesched.go. The only type needed by this interface is
FrameWriteRequest, which describes a request to write a frame (this used
to be called frameWriteMsg). The scheduler can be configured with a new
field in http2.Server. Two schedulers are implemented:

1) A random scheduler that is essentially equivalent to the existing
   scheduler. This is currently the default scheduler if none is
   configured. The implementation is in writesched_random.go.

2) A scheduler that uses H2 weights and priorities. The H2 priority tree
   is maintained as a tree of priorityNodes. The next frame is chosen by
   walking this tree in topological order, where sibling nodes are ordered
   by their bandwidth usage relative to their H2 weight. Two optional
   features are added to improve performance -- these are configured with
   PriorityWriteSchedulerConfig.

Fixes golang/go#16168

Change-Id: I97ec93e5c58c2efec35455ba2f3c31e849f706af
Reviewed-on: https://go-review.googlesource.com/25366Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

http2/priority_test.go

-// Copyright 2014 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 (
-	"testing"
-)
-
-func TestPriority(t *testing.T) {
-	// A -> B
-	// move A's parent to B
-	streams := make(map[uint32]*stream)
-	a := &stream{
-		parent: nil,
-		weight: 16,
-	}
-	streams[1] = a
-	b := &stream{
-		parent: a,
-		weight: 16,
-	}
-	streams[2] = b
-	adjustStreamPriority(streams, 1, PriorityParam{
-		Weight:    20,
-		StreamDep: 2,
-	})
-	if a.parent != b {
-		t.Errorf("Expected A's parent to be B")
-	}
-	if a.weight != 20 {
-		t.Errorf("Expected A's weight to be 20; got %d", a.weight)
-	}
-	if b.parent != nil {
-		t.Errorf("Expected B to have no parent")
-	}
-	if b.weight != 16 {
-		t.Errorf("Expected B's weight to be 16; got %d", b.weight)
-	}
-}
-
-func TestPriorityExclusiveZero(t *testing.T) {
-	// A B and C are all children of the 0 stream.
-	// Exclusive reprioritization to any of the streams
-	// should bring the rest of the streams under the
-	// reprioritized stream
-	streams := make(map[uint32]*stream)
-	a := &stream{
-		parent: nil,
-		weight: 16,
-	}
-	streams[1] = a
-	b := &stream{
-		parent: nil,
-		weight: 16,
-	}
-	streams[2] = b
-	c := &stream{
-		parent: nil,
-		weight: 16,
-	}
-	streams[3] = c
-	adjustStreamPriority(streams, 3, PriorityParam{
-		Weight:    20,
-		StreamDep: 0,
-		Exclusive: true,
-	})
-	if a.parent != c {
-		t.Errorf("Expected A's parent to be C")
-	}
-	if a.weight != 16 {
-		t.Errorf("Expected A's weight to be 16; got %d", a.weight)
-	}
-	if b.parent != c {
-		t.Errorf("Expected B's parent to be C")
-	}
-	if b.weight != 16 {
-		t.Errorf("Expected B's weight to be 16; got %d", b.weight)
-	}
-	if c.parent != nil {
-		t.Errorf("Expected C to have no parent")
-	}
-	if c.weight != 20 {
-		t.Errorf("Expected C's weight to be 20; got %d", b.weight)
-	}
-}
-
-func TestPriorityOwnParent(t *testing.T) {
-	streams := make(map[uint32]*stream)
-	a := &stream{
-		parent: nil,
-		weight: 16,
-	}
-	streams[1] = a
-	b := &stream{
-		parent: a,
-		weight: 16,
-	}
-	streams[2] = b
-	adjustStreamPriority(streams, 1, PriorityParam{
-		Weight:    20,
-		StreamDep: 1,
-	})
-	if a.parent != nil {
-		t.Errorf("Expected A's parent to be nil")
-	}
-	if a.weight != 20 {
-		t.Errorf("Expected A's weight to be 20; got %d", a.weight)
-	}
-	if b.parent != a {
-		t.Errorf("Expected B's parent to be A")
-	}
-	if b.weight != 16 {
-		t.Errorf("Expected B's weight to be 16; got %d", b.weight)
-	}
-
-}

http2/writesched_random.go

+// Copyright 2014 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 "math"
+
+// NewRandomWriteScheduler constructs a WriteScheduler that ignores HTTP/2
+// priorities. Control frames like SETTINGS and PING are written before DATA
+// frames, but if no control frames are queued and multiple streams have queued
+// HEADERS or DATA frames, Pop selects a ready stream arbitrarily.
+func NewRandomWriteScheduler() WriteScheduler {
+	return &randomWriteScheduler{sq: make(map[uint32]*writeQueue)}
+}
+
+type randomWriteScheduler struct {
+	// zero are frames not associated with a specific stream.
+	zero writeQueue
+
+	// sq contains the stream-specific queues, keyed by stream ID.
+	// When a stream is idle or closed, it's deleted from the map.
+	sq map[uint32]*writeQueue
+
+	// pool of empty queues for reuse.
+	queuePool writeQueuePool
+}
+
+func (ws *randomWriteScheduler) OpenStream(streamID uint32, options OpenStreamOptions) {
+	// no-op: idle streams are not tracked
+}
+
+func (ws *randomWriteScheduler) CloseStream(streamID uint32) {
+	q, ok := ws.sq[streamID]
+	if !ok {
+		return
+	}
+	delete(ws.sq, streamID)
+	ws.queuePool.put(q)
+}
+
+func (ws *randomWriteScheduler) AdjustStream(streamID uint32, priority PriorityParam) {
+	// no-op: priorities are ignored
+}
+
+func (ws *randomWriteScheduler) Push(wr FrameWriteRequest) {
+	id := wr.StreamID()
+	if id == 0 {
+		ws.zero.push(wr)
+		return
+	}
+	q, ok := ws.sq[id]
+	if !ok {
+		q = ws.queuePool.get()
+		ws.sq[id] = q
+	}
+	q.push(wr)
+}
+
+func (ws *randomWriteScheduler) Pop() (FrameWriteRequest, bool) {
+	// Control frames first.
+	if !ws.zero.empty() {
+		return ws.zero.shift(), true
+	}
+	// Iterate over all non-idle streams until finding one that can be consumed.
+	for _, q := range ws.sq {
+		if wr, ok := q.consume(math.MaxInt32); ok {
+			return wr, true
+		}
+	}
+	return FrameWriteRequest{}, false
+}

http2/writesched_random_test.go

+// Copyright 2016 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 "testing"
+
+func TestRandomScheduler(t *testing.T) {
+	ws := NewRandomWriteScheduler()
+	ws.Push(makeWriteHeadersRequest(3))
+	ws.Push(makeWriteHeadersRequest(4))
+	ws.Push(makeWriteHeadersRequest(1))
+	ws.Push(makeWriteHeadersRequest(2))
+	ws.Push(makeWriteNonStreamRequest())
+	ws.Push(makeWriteNonStreamRequest())
+
+	// Pop all frames. Should get the non-stream requests first,
+	// followed by the stream requests in any order.
+	var order []FrameWriteRequest
+	for {
+		wr, ok := ws.Pop()
+		if !ok {
+			break
+		}
+		order = append(order, wr)
+	}
+	t.Logf("got frames: %v", order)
+	if len(order) != 6 {
+		t.Fatalf("got %d frames, expected 6", len(order))
+	}
+	if order[0].StreamID() != 0 || order[1].StreamID() != 0 {
+		t.Fatalf("expected non-stream frames first", order[0], order[1])
+	}
+	got := make(map[uint32]bool)
+	for _, wr := range order[2:] {
+		got[wr.StreamID()] = true
+	}
+	for id := uint32(1); id <= 4; id++ {
+		if !got[id] {
+			t.Errorf("frame not found for stream %d", id)
+		}
+	}
+}

http2/writesched_test.go

+// Copyright 2016 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"
+	"reflect"
+	"testing"
+)
+
+func makeWriteNonStreamRequest() FrameWriteRequest {
+	return FrameWriteRequest{writeSettingsAck{}, nil, nil}
+}
+
+func makeWriteHeadersRequest(streamID uint32) FrameWriteRequest {
+	st := &stream{id: streamID}
+	return FrameWriteRequest{&writeResHeaders{streamID: streamID, httpResCode: 200}, st, nil}
+}
+
+func checkConsume(wr FrameWriteRequest, nbytes int32, want []FrameWriteRequest) error {
+	consumed, rest, n := wr.Consume(nbytes)
+	var wantConsumed, wantRest FrameWriteRequest
+	switch len(want) {
+	case 0:
+	case 1:
+		wantConsumed = want[0]
+	case 2:
+		wantConsumed = want[0]
+		wantRest = want[1]
+	}
+	if !reflect.DeepEqual(consumed, wantConsumed) || !reflect.DeepEqual(rest, wantRest) || n != len(want) {
+		return fmt.Errorf("got %v, %v, %v\nwant %v, %v, %v", consumed, rest, n, wantConsumed, wantRest, len(want))
+	}
+	return nil
+}
+
+func TestFrameWriteRequestNonData(t *testing.T) {
+	wr := makeWriteNonStreamRequest()
+	if got, want := wr.DataSize(), 0; got != want {
+		t.Errorf("DataSize: got %v, want %v", got, want)
+	}
+
+	// Non-DATA frames are always consumed whole.
+	if err := checkConsume(wr, 0, []FrameWriteRequest{wr}); err != nil {
+		t.Errorf("Consume:\n%v", err)
+	}
+}
+
+func TestFrameWriteRequestData(t *testing.T) {
+	st := &stream{
+		id: 1,
+		sc: &serverConn{maxFrameSize: 16},
+	}
+	const size = 32
+	wr := FrameWriteRequest{&writeData{st.id, make([]byte, size), true}, st, make(chan error)}
+	if got, want := wr.DataSize(), size; got != want {
+		t.Errorf("DataSize: got %v, want %v", got, want)
+	}
+
+	// No flow-control bytes available: cannot consume anything.
+	if err := checkConsume(wr, math.MaxInt32, []FrameWriteRequest{}); err != nil {
+		t.Errorf("Consume(limited by flow control):\n%v", err)
+	}
+
+	// Add enough flow-control bytes to consume the entire frame,
+	// but we're now restricted by st.sc.maxFrameSize.
+	st.flow.add(size)
+	want := []FrameWriteRequest{
+		{
+			write:  &writeData{st.id, make([]byte, st.sc.maxFrameSize), false},
+			stream: st,
+			done:   nil,
+		},
+		{
+			write:  &writeData{st.id, make([]byte, size-st.sc.maxFrameSize), true},
+			stream: st,
+			done:   wr.done,
+		},
+	}
+	if err := checkConsume(wr, math.MaxInt32, want); err != nil {
+		t.Errorf("Consume(limited by maxFrameSize):\n%v", err)
+	}
+	rest := want[1]
+
+	// Consume 8 bytes from the remaining frame.
+	want = []FrameWriteRequest{
+		{
+			write:  &writeData{st.id, make([]byte, 8), false},
+			stream: st,
+			done:   nil,
+		},
+		{
+			write:  &writeData{st.id, make([]byte, size-st.sc.maxFrameSize-8), true},
+			stream: st,
+			done:   wr.done,
+		},
+	}
+	if err := checkConsume(rest, 8, want); err != nil {
+		t.Errorf("Consume(8):\n%v", err)
+	}
+	rest = want[1]
+
+	// Consume all remaining bytes.
+	want = []FrameWriteRequest{
+		{
+			write:  &writeData{st.id, make([]byte, size-st.sc.maxFrameSize-8), true},
+			stream: st,
+			done:   wr.done,
+		},
+	}
+	if err := checkConsume(rest, math.MaxInt32, want); err != nil {
+		t.Errorf("Consume(remainder):\n%v", err)
+	}
+}