132 lines
3.6 KiB
Go
132 lines
3.6 KiB
Go
// Copyright 2019 The etcd Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package tracker
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// Inflights limits the number of MsgApp (represented by the largest index
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// contained within) sent to followers but not yet acknowledged by them. Callers
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// use Full() to check whether more messages can be sent, call Add() whenever
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// they are sending a new append, and release "quota" via FreeLE() whenever an
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// ack is received.
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type Inflights struct {
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// the starting index in the buffer
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start int
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// number of inflights in the buffer
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count int
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// the size of the buffer
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size int
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// buffer contains the index of the last entry
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// inside one message.
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buffer []uint64
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}
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// NewInflights sets up an Inflights that allows up to 'size' inflight messages.
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func NewInflights(size int) *Inflights {
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return &Inflights{
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size: size,
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}
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}
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// Clone returns an *Inflights that is identical to but shares no memory with
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// the receiver.
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func (in *Inflights) Clone() *Inflights {
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ins := *in
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ins.buffer = append([]uint64(nil), in.buffer...)
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return &ins
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}
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// Add notifies the Inflights that a new message with the given index is being
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// dispatched. Full() must be called prior to Add() to verify that there is room
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// for one more message, and consecutive calls to add Add() must provide a
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// monotonic sequence of indexes.
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func (in *Inflights) Add(inflight uint64) {
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if in.Full() {
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panic("cannot add into a Full inflights")
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}
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next := in.start + in.count
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size := in.size
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if next >= size {
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next -= size
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}
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if next >= len(in.buffer) {
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in.grow()
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}
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in.buffer[next] = inflight
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in.count++
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}
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// grow the inflight buffer by doubling up to inflights.size. We grow on demand
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// instead of preallocating to inflights.size to handle systems which have
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// thousands of Raft groups per process.
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func (in *Inflights) grow() {
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newSize := len(in.buffer) * 2
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if newSize == 0 {
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newSize = 1
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} else if newSize > in.size {
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newSize = in.size
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}
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newBuffer := make([]uint64, newSize)
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copy(newBuffer, in.buffer)
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in.buffer = newBuffer
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}
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// FreeLE frees the inflights smaller or equal to the given `to` flight.
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func (in *Inflights) FreeLE(to uint64) {
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if in.count == 0 || to < in.buffer[in.start] {
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// out of the left side of the window
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return
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}
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idx := in.start
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var i int
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for i = 0; i < in.count; i++ {
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if to < in.buffer[idx] { // found the first large inflight
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break
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}
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// increase index and maybe rotate
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size := in.size
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if idx++; idx >= size {
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idx -= size
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}
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}
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// free i inflights and set new start index
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in.count -= i
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in.start = idx
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if in.count == 0 {
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// inflights is empty, reset the start index so that we don't grow the
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// buffer unnecessarily.
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in.start = 0
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}
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}
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// FreeFirstOne releases the first inflight. This is a no-op if nothing is
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// inflight.
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func (in *Inflights) FreeFirstOne() { in.FreeLE(in.buffer[in.start]) }
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// Full returns true if no more messages can be sent at the moment.
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func (in *Inflights) Full() bool {
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return in.count == in.size
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}
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// Count returns the number of inflight messages.
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func (in *Inflights) Count() int { return in.count }
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// reset frees all inflights.
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func (in *Inflights) reset() {
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in.count = 0
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in.start = 0
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}
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