diff --git a/http2/writesched.go b/http2/writesched.go index 4d3890f9..7de27be5 100644 --- a/http2/writesched.go +++ b/http2/writesched.go @@ -185,45 +185,75 @@ func (wr *FrameWriteRequest) replyToWriter(err error) { } // writeQueue is used by implementations of WriteScheduler. +// +// Each writeQueue contains a queue of FrameWriteRequests, meant to store all +// FrameWriteRequests associated with a given stream. This is implemented as a +// two-stage queue: currQueue[currPos:] and nextQueue. Removing an item is done +// by incrementing currPos of currQueue. Adding an item is done by appending it +// to the nextQueue. If currQueue is empty when trying to remove an item, we +// can swap currQueue and nextQueue to remedy the situation. +// This two-stage queue is analogous to the use of two lists in Okasaki's +// purely functional queue but without the overhead of reversing the list when +// swapping stages. +// +// writeQueue also contains prev and next, this can be used by implementations +// of WriteScheduler to construct data structures that represent the order of +// writing between different streams (e.g. circular linked list). type writeQueue struct { - s []FrameWriteRequest + currQueue []FrameWriteRequest + nextQueue []FrameWriteRequest + currPos int + prev, next *writeQueue } -func (q *writeQueue) empty() bool { return len(q.s) == 0 } +func (q *writeQueue) empty() bool { + return (len(q.currQueue) - q.currPos + len(q.nextQueue)) == 0 +} func (q *writeQueue) push(wr FrameWriteRequest) { - q.s = append(q.s, wr) + q.nextQueue = append(q.nextQueue, wr) } func (q *writeQueue) shift() FrameWriteRequest { - if len(q.s) == 0 { + if q.empty() { panic("invalid use of queue") } - wr := q.s[0] - // TODO: less copy-happy queue. - copy(q.s, q.s[1:]) - q.s[len(q.s)-1] = FrameWriteRequest{} - q.s = q.s[:len(q.s)-1] + if q.currPos >= len(q.currQueue) { + q.currQueue, q.currPos, q.nextQueue = q.nextQueue, 0, q.currQueue[:0] + } + wr := q.currQueue[q.currPos] + q.currQueue[q.currPos] = FrameWriteRequest{} + q.currPos++ return wr } +func (q *writeQueue) peek() *FrameWriteRequest { + if q.currPos < len(q.currQueue) { + return &q.currQueue[q.currPos] + } + if len(q.nextQueue) > 0 { + return &q.nextQueue[0] + } + return nil +} + // consume consumes up to n bytes from q.s[0]. If the frame is // entirely consumed, it is removed from the queue. If the frame // is partially consumed, the frame is kept with the consumed // bytes removed. Returns true iff any bytes were consumed. func (q *writeQueue) consume(n int32) (FrameWriteRequest, bool) { - if len(q.s) == 0 { + if q.empty() { return FrameWriteRequest{}, false } - consumed, rest, numresult := q.s[0].Consume(n) + consumed, rest, numresult := q.peek().Consume(n) switch numresult { case 0: return FrameWriteRequest{}, false case 1: q.shift() case 2: - q.s[0] = rest + *q.peek() = rest } return consumed, true } @@ -232,10 +262,15 @@ type writeQueuePool []*writeQueue // put inserts an unused writeQueue into the pool. func (p *writeQueuePool) put(q *writeQueue) { - for i := range q.s { - q.s[i] = FrameWriteRequest{} + for i := range q.currQueue { + q.currQueue[i] = FrameWriteRequest{} } - q.s = q.s[:0] + for i := range q.nextQueue { + q.nextQueue[i] = FrameWriteRequest{} + } + q.currQueue = q.currQueue[:0] + q.nextQueue = q.nextQueue[:0] + q.currPos = 0 *p = append(*p, q) } diff --git a/http2/writesched_benchmarks_test.go b/http2/writesched_benchmarks_test.go index 274f5041..5663a523 100644 --- a/http2/writesched_benchmarks_test.go +++ b/http2/writesched_benchmarks_test.go @@ -178,3 +178,20 @@ func BenchmarkWriteSchedulerLifetimePriorityRFC9218NonIncremental(b *testing.B) incremental: 0, }) } + +func BenchmarkWriteQueue(b *testing.B) { + var qp writeQueuePool + frameCount := 25 + for b.Loop() { + q := qp.get() + for range frameCount { + q.push(FrameWriteRequest{}) + } + for !q.empty() { + // Since we pushed empty frames, consuming 1 byte is enough to + // consume the entire frame. + q.consume(1) + } + qp.put(q) + } +} diff --git a/http2/writesched_priority_rfc7540.go b/http2/writesched_priority_rfc7540.go index 6d24d6a1..fb9e260a 100644 --- a/http2/writesched_priority_rfc7540.go +++ b/http2/writesched_priority_rfc7540.go @@ -302,7 +302,6 @@ func (ws *priorityWriteSchedulerRFC7540) CloseStream(streamID uint32) { q := n.q ws.queuePool.put(&q) - n.q.s = nil if ws.maxClosedNodesInTree > 0 { ws.addClosedOrIdleNode(&ws.closedNodes, ws.maxClosedNodesInTree, n) } else {