From e0a1ccb64a637673195804513902cba6b1d4e97c Mon Sep 17 00:00:00 2001 From: Niall Sheridan Date: Mon, 31 Oct 2016 16:36:17 +0000 Subject: Update dependencies --- .../golang.org/x/net/http2/writesched_priority.go | 444 +++++++++++++++++++++ 1 file changed, 444 insertions(+) create mode 100644 vendor/golang.org/x/net/http2/writesched_priority.go (limited to 'vendor/golang.org/x/net/http2/writesched_priority.go') diff --git a/vendor/golang.org/x/net/http2/writesched_priority.go b/vendor/golang.org/x/net/http2/writesched_priority.go new file mode 100644 index 0000000..40108b0 --- /dev/null +++ b/vendor/golang.org/x/net/http2/writesched_priority.go @@ -0,0 +1,444 @@ +// 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" + "sort" +) + +// RFC 7540, Section 5.3.5: the default weight is 16. +const priorityDefaultWeight = 15 // 16 = 15 + 1 + +// PriorityWriteSchedulerConfig configures a priorityWriteScheduler. +type PriorityWriteSchedulerConfig struct { + // MaxClosedNodesInTree controls the maximum number of closed streams to + // retain in the priority tree. Setting this to zero saves a small amount + // of memory at the cost of performance. + // + // See RFC 7540, Section 5.3.4: + // "It is possible for a stream to become closed while prioritization + // information ... is in transit. ... This potentially creates suboptimal + // prioritization, since the stream could be given a priority that is + // different from what is intended. To avoid these problems, an endpoint + // SHOULD retain stream prioritization state for a period after streams + // become closed. The longer state is retained, the lower the chance that + // streams are assigned incorrect or default priority values." + MaxClosedNodesInTree int + + // MaxIdleNodesInTree controls the maximum number of idle streams to + // retain in the priority tree. Setting this to zero saves a small amount + // of memory at the cost of performance. + // + // See RFC 7540, Section 5.3.4: + // Similarly, streams that are in the "idle" state can be assigned + // priority or become a parent of other streams. This allows for the + // creation of a grouping node in the dependency tree, which enables + // more flexible expressions of priority. Idle streams begin with a + // default priority (Section 5.3.5). + MaxIdleNodesInTree int + + // ThrottleOutOfOrderWrites enables write throttling to help ensure that + // data is delivered in priority order. This works around a race where + // stream B depends on stream A and both streams are about to call Write + // to queue DATA frames. If B wins the race, a naive scheduler would eagerly + // write as much data from B as possible, but this is suboptimal because A + // is a higher-priority stream. With throttling enabled, we write a small + // amount of data from B to minimize the amount of bandwidth that B can + // steal from A. + ThrottleOutOfOrderWrites bool +} + +// NewPriorityWriteScheduler constructs a WriteScheduler that schedules +// frames by following HTTP/2 priorities as described in RFC 7340 Section 5.3. +// If cfg is nil, default options are used. +func NewPriorityWriteScheduler(cfg *PriorityWriteSchedulerConfig) WriteScheduler { + if cfg == nil { + // For justification of these defaults, see: + // https://docs.google.com/document/d/1oLhNg1skaWD4_DtaoCxdSRN5erEXrH-KnLrMwEpOtFY + cfg = &PriorityWriteSchedulerConfig{ + MaxClosedNodesInTree: 10, + MaxIdleNodesInTree: 10, + ThrottleOutOfOrderWrites: false, + } + } + + ws := &priorityWriteScheduler{ + nodes: make(map[uint32]*priorityNode), + maxClosedNodesInTree: cfg.MaxClosedNodesInTree, + maxIdleNodesInTree: cfg.MaxIdleNodesInTree, + enableWriteThrottle: cfg.ThrottleOutOfOrderWrites, + } + ws.nodes[0] = &ws.root + if cfg.ThrottleOutOfOrderWrites { + ws.writeThrottleLimit = 1024 + } else { + ws.writeThrottleLimit = math.MaxInt32 + } + return ws +} + +type priorityNodeState int + +const ( + priorityNodeOpen priorityNodeState = iota + priorityNodeClosed + priorityNodeIdle +) + +// priorityNode is a node in an HTTP/2 priority tree. +// Each node is associated with a single stream ID. +// See RFC 7540, Section 5.3. +type priorityNode struct { + q writeQueue // queue of pending frames to write + id uint32 // id of the stream, or 0 for the root of the tree + weight uint8 // the actual weight is weight+1, so the value is in [1,256] + state priorityNodeState // open | closed | idle + bytes int64 // number of bytes written by this node, or 0 if closed + subtreeBytes int64 // sum(node.bytes) of all nodes in this subtree + + // These links form the priority tree. + parent *priorityNode + kids *priorityNode // start of the kids list + prev, next *priorityNode // doubly-linked list of siblings +} + +func (n *priorityNode) setParent(parent *priorityNode) { + if n == parent { + panic("setParent to self") + } + if n.parent == parent { + return + } + // Unlink from current parent. + if parent := n.parent; parent != nil { + if n.prev == nil { + parent.kids = n.next + } else { + n.prev.next = n.next + } + if n.next != nil { + n.next.prev = n.prev + } + } + // Link to new parent. + // If parent=nil, remove n from the tree. + // Always insert at the head of parent.kids (this is assumed by walkReadyInOrder). + n.parent = parent + if parent == nil { + n.next = nil + n.prev = nil + } else { + n.next = parent.kids + n.prev = nil + if n.next != nil { + n.next.prev = n + } + parent.kids = n + } +} + +func (n *priorityNode) addBytes(b int64) { + n.bytes += b + for ; n != nil; n = n.parent { + n.subtreeBytes += b + } +} + +// walkReadyInOrder iterates over the tree in priority order, calling f for each node +// with a non-empty write queue. When f returns true, this funcion returns true and the +// walk halts. tmp is used as scratch space for sorting. +// +// f(n, openParent) takes two arguments: the node to visit, n, and a bool that is true +// if any ancestor p of n is still open (ignoring the root node). +func (n *priorityNode) walkReadyInOrder(openParent bool, tmp *[]*priorityNode, f func(*priorityNode, bool) bool) bool { + if !n.q.empty() && f(n, openParent) { + return true + } + if n.kids == nil { + return false + } + + // Don't consider the root "open" when updating openParent since + // we can't send data frames on the root stream (only control frames). + if n.id != 0 { + openParent = openParent || (n.state == priorityNodeOpen) + } + + // Common case: only one kid or all kids have the same weight. + // Some clients don't use weights; other clients (like web browsers) + // use mostly-linear priority trees. + w := n.kids.weight + needSort := false + for k := n.kids.next; k != nil; k = k.next { + if k.weight != w { + needSort = true + break + } + } + if !needSort { + for k := n.kids; k != nil; k = k.next { + if k.walkReadyInOrder(openParent, tmp, f) { + return true + } + } + return false + } + + // Uncommon case: sort the child nodes. We remove the kids from the parent, + // then re-insert after sorting so we can reuse tmp for future sort calls. + *tmp = (*tmp)[:0] + for n.kids != nil { + *tmp = append(*tmp, n.kids) + n.kids.setParent(nil) + } + sort.Sort(sortPriorityNodeSiblings(*tmp)) + for i := len(*tmp) - 1; i >= 0; i-- { + (*tmp)[i].setParent(n) // setParent inserts at the head of n.kids + } + for k := n.kids; k != nil; k = k.next { + if k.walkReadyInOrder(openParent, tmp, f) { + return true + } + } + return false +} + +type sortPriorityNodeSiblings []*priorityNode + +func (z sortPriorityNodeSiblings) Len() int { return len(z) } +func (z sortPriorityNodeSiblings) Swap(i, k int) { z[i], z[k] = z[k], z[i] } +func (z sortPriorityNodeSiblings) Less(i, k int) bool { + // Prefer the subtree that has sent fewer bytes relative to its weight. + // See sections 5.3.2 and 5.3.4. + wi, bi := float64(z[i].weight+1), float64(z[i].subtreeBytes) + wk, bk := float64(z[k].weight+1), float64(z[k].subtreeBytes) + if bi == 0 && bk == 0 { + return wi >= wk + } + if bk == 0 { + return false + } + return bi/bk <= wi/wk +} + +type priorityWriteScheduler struct { + // root is the root of the priority tree, where root.id = 0. + // The root queues control frames that are not associated with any stream. + root priorityNode + + // nodes maps stream ids to priority tree nodes. + nodes map[uint32]*priorityNode + + // maxID is the maximum stream id in nodes. + maxID uint32 + + // lists of nodes that have been closed or are idle, but are kept in + // the tree for improved prioritization. When the lengths exceed either + // maxClosedNodesInTree or maxIdleNodesInTree, old nodes are discarded. + closedNodes, idleNodes []*priorityNode + + // From the config. + maxClosedNodesInTree int + maxIdleNodesInTree int + writeThrottleLimit int32 + enableWriteThrottle bool + + // tmp is scratch space for priorityNode.walkReadyInOrder to reduce allocations. + tmp []*priorityNode + + // pool of empty queues for reuse. + queuePool writeQueuePool +} + +func (ws *priorityWriteScheduler) OpenStream(streamID uint32, options OpenStreamOptions) { + // The stream may be currently idle but cannot be opened or closed. + if curr := ws.nodes[streamID]; curr != nil { + if curr.state != priorityNodeIdle { + panic(fmt.Sprintf("stream %d already opened", streamID)) + } + curr.state = priorityNodeOpen + return + } + + // RFC 7540, Section 5.3.5: + // "All streams are initially assigned a non-exclusive dependency on stream 0x0. + // Pushed streams initially depend on their associated stream. In both cases, + // streams are assigned a default weight of 16." + parent := ws.nodes[options.PusherID] + if parent == nil { + parent = &ws.root + } + n := &priorityNode{ + q: *ws.queuePool.get(), + id: streamID, + weight: priorityDefaultWeight, + state: priorityNodeOpen, + } + n.setParent(parent) + ws.nodes[streamID] = n + if streamID > ws.maxID { + ws.maxID = streamID + } +} + +func (ws *priorityWriteScheduler) CloseStream(streamID uint32) { + if streamID == 0 { + panic("violation of WriteScheduler interface: cannot close stream 0") + } + if ws.nodes[streamID] == nil { + panic(fmt.Sprintf("violation of WriteScheduler interface: unknown stream %d", streamID)) + } + if ws.nodes[streamID].state != priorityNodeOpen { + panic(fmt.Sprintf("violation of WriteScheduler interface: stream %d already closed", streamID)) + } + + n := ws.nodes[streamID] + n.state = priorityNodeClosed + n.addBytes(-n.bytes) + + q := n.q + ws.queuePool.put(&q) + n.q.s = nil + if ws.maxClosedNodesInTree > 0 { + ws.addClosedOrIdleNode(&ws.closedNodes, ws.maxClosedNodesInTree, n) + } else { + ws.removeNode(n) + } +} + +func (ws *priorityWriteScheduler) AdjustStream(streamID uint32, priority PriorityParam) { + if streamID == 0 { + panic("adjustPriority on root") + } + + // If streamID does not exist, there are two cases: + // - A closed stream that has been removed (this will have ID <= maxID) + // - An idle stream that is being used for "grouping" (this will have ID > maxID) + n := ws.nodes[streamID] + if n == nil { + if streamID <= ws.maxID || ws.maxIdleNodesInTree == 0 { + return + } + ws.maxID = streamID + n = &priorityNode{ + q: *ws.queuePool.get(), + id: streamID, + weight: priorityDefaultWeight, + state: priorityNodeIdle, + } + n.setParent(&ws.root) + ws.nodes[streamID] = n + ws.addClosedOrIdleNode(&ws.idleNodes, ws.maxIdleNodesInTree, n) + } + + // Section 5.3.1: A dependency on a stream that is not currently in the tree + // results in that stream being given a default priority (Section 5.3.5). + parent := ws.nodes[priority.StreamDep] + if parent == nil { + n.setParent(&ws.root) + n.weight = priorityDefaultWeight + return + } + + // Ignore if the client tries to make a node its own parent. + if n == parent { + return + } + + // Section 5.3.3: + // "If a stream is made dependent on one of its own dependencies, the + // formerly dependent stream is first moved to be dependent on the + // reprioritized stream's previous parent. The moved dependency retains + // its weight." + // + // That is: if parent depends on n, move parent to depend on n.parent. + for x := parent.parent; x != nil; x = x.parent { + if x == n { + parent.setParent(n.parent) + break + } + } + + // Section 5.3.3: The exclusive flag causes the stream to become the sole + // dependency of its parent stream, causing other dependencies to become + // dependent on the exclusive stream. + if priority.Exclusive { + k := parent.kids + for k != nil { + next := k.next + if k != n { + k.setParent(n) + } + k = next + } + } + + n.setParent(parent) + n.weight = priority.Weight +} + +func (ws *priorityWriteScheduler) Push(wr FrameWriteRequest) { + var n *priorityNode + if id := wr.StreamID(); id == 0 { + n = &ws.root + } else { + n = ws.nodes[id] + if n == nil { + panic("add on non-open stream") + } + } + n.q.push(wr) +} + +func (ws *priorityWriteScheduler) Pop() (wr FrameWriteRequest, ok bool) { + ws.root.walkReadyInOrder(false, &ws.tmp, func(n *priorityNode, openParent bool) bool { + limit := int32(math.MaxInt32) + if openParent { + limit = ws.writeThrottleLimit + } + wr, ok = n.q.consume(limit) + if !ok { + return false + } + n.addBytes(int64(wr.DataSize())) + // If B depends on A and B continuously has data available but A + // does not, gradually increase the throttling limit to allow B to + // steal more and more bandwidth from A. + if openParent { + ws.writeThrottleLimit += 1024 + if ws.writeThrottleLimit < 0 { + ws.writeThrottleLimit = math.MaxInt32 + } + } else if ws.enableWriteThrottle { + ws.writeThrottleLimit = 1024 + } + return true + }) + return wr, ok +} + +func (ws *priorityWriteScheduler) addClosedOrIdleNode(list *[]*priorityNode, maxSize int, n *priorityNode) { + if maxSize == 0 { + return + } + if len(*list) == maxSize { + // Remove the oldest node, then shift left. + ws.removeNode((*list)[0]) + x := (*list)[1:] + copy(*list, x) + *list = (*list)[:len(x)] + } + *list = append(*list, n) +} + +func (ws *priorityWriteScheduler) removeNode(n *priorityNode) { + for k := n.kids; k != nil; k = k.next { + k.setParent(n.parent) + } + n.setParent(nil) + delete(ws.nodes, n.id) +} -- cgit v1.2.3