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Diffstat (limited to 'vendor/golang.org/x/net/http2/writesched_priority.go')
| -rw-r--r-- | vendor/golang.org/x/net/http2/writesched_priority.go | 452 |
1 files changed, 0 insertions, 452 deletions
diff --git a/vendor/golang.org/x/net/http2/writesched_priority.go b/vendor/golang.org/x/net/http2/writesched_priority.go deleted file mode 100644 index 848fed6..0000000 --- a/vendor/golang.org/x/net/http2/writesched_priority.go +++ /dev/null @@ -1,452 +0,0 @@ -// 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 7540 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 { - // id is an idle or closed stream. wr should not be a HEADERS or - // DATA frame. However, wr can be a RST_STREAM. In this case, we - // push wr onto the root, rather than creating a new priorityNode, - // since RST_STREAM is tiny and the stream's priority is unknown - // anyway. See issue #17919. - if wr.DataSize() > 0 { - panic("add DATA on non-open stream") - } - n = &ws.root - } - } - 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) -} |