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// Copyright 2016 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
// Package flowcontrol implements a client side flow control mechanism
package flowcontrol
import (
"sync"
"time"
"github.com/ethereum/go-ethereum/common/mclock"
)
const fcTimeConst = time.Millisecond
type ServerParams struct {
BufLimit, MinRecharge uint64
}
type ClientNode struct {
params *ServerParams
bufValue uint64
lastTime mclock.AbsTime
lock sync.Mutex
cm *ClientManager
cmNode *cmNode
}
func NewClientNode(cm *ClientManager, params *ServerParams) *ClientNode {
node := &ClientNode{
cm: cm,
params: params,
bufValue: params.BufLimit,
lastTime: mclock.Now(),
}
node.cmNode = cm.addNode(node)
return node
}
func (peer *ClientNode) Remove(cm *ClientManager) {
cm.removeNode(peer.cmNode)
}
func (peer *ClientNode) recalcBV(time mclock.AbsTime) {
dt := uint64(time - peer.lastTime)
if time < peer.lastTime {
dt = 0
}
peer.bufValue += peer.params.MinRecharge * dt / uint64(fcTimeConst)
if peer.bufValue > peer.params.BufLimit {
peer.bufValue = peer.params.BufLimit
}
peer.lastTime = time
}
func (peer *ClientNode) AcceptRequest() (uint64, bool) {
peer.lock.Lock()
defer peer.lock.Unlock()
time := mclock.Now()
peer.recalcBV(time)
return peer.bufValue, peer.cm.accept(peer.cmNode, time)
}
func (peer *ClientNode) RequestProcessed(cost uint64) (bv, realCost uint64) {
peer.lock.Lock()
defer peer.lock.Unlock()
time := mclock.Now()
peer.recalcBV(time)
peer.bufValue -= cost
peer.recalcBV(time)
rcValue, rcost := peer.cm.processed(peer.cmNode, time)
if rcValue < peer.params.BufLimit {
bv := peer.params.BufLimit - rcValue
if bv > peer.bufValue {
peer.bufValue = bv
}
}
return peer.bufValue, rcost
}
type ServerNode struct {
bufEstimate uint64
lastTime mclock.AbsTime
params *ServerParams
sumCost uint64 // sum of req costs sent to this server
pending map[uint64]uint64 // value = sumCost after sending the given req
lock sync.RWMutex
}
func NewServerNode(params *ServerParams) *ServerNode {
return &ServerNode{
bufEstimate: params.BufLimit,
lastTime: mclock.Now(),
params: params,
pending: make(map[uint64]uint64),
}
}
func (peer *ServerNode) recalcBLE(time mclock.AbsTime) {
dt := uint64(time - peer.lastTime)
if time < peer.lastTime {
dt = 0
}
peer.bufEstimate += peer.params.MinRecharge * dt / uint64(fcTimeConst)
if peer.bufEstimate > peer.params.BufLimit {
peer.bufEstimate = peer.params.BufLimit
}
peer.lastTime = time
}
// safetyMargin is added to the flow control waiting time when estimated buffer value is low
const safetyMargin = time.Millisecond
func (peer *ServerNode) canSend(maxCost uint64) (time.Duration, float64) {
peer.recalcBLE(mclock.Now())
maxCost += uint64(safetyMargin) * peer.params.MinRecharge / uint64(fcTimeConst)
if maxCost > peer.params.BufLimit {
maxCost = peer.params.BufLimit
}
if peer.bufEstimate >= maxCost {
return 0, float64(peer.bufEstimate-maxCost) / float64(peer.params.BufLimit)
}
return time.Duration((maxCost - peer.bufEstimate) * uint64(fcTimeConst) / peer.params.MinRecharge), 0
}
// CanSend returns the minimum waiting time required before sending a request
// with the given maximum estimated cost. Second return value is the relative
// estimated buffer level after sending the request (divided by BufLimit).
func (peer *ServerNode) CanSend(maxCost uint64) (time.Duration, float64) {
peer.lock.RLock()
defer peer.lock.RUnlock()
return peer.canSend(maxCost)
}
// QueueRequest should be called when the request has been assigned to the given
// server node, before putting it in the send queue. It is mandatory that requests
// are sent in the same order as the QueueRequest calls are made.
func (peer *ServerNode) QueueRequest(reqID, maxCost uint64) {
peer.lock.Lock()
defer peer.lock.Unlock()
peer.bufEstimate -= maxCost
peer.sumCost += maxCost
peer.pending[reqID] = peer.sumCost
}
// GotReply adjusts estimated buffer value according to the value included in
// the latest request reply.
func (peer *ServerNode) GotReply(reqID, bv uint64) {
peer.lock.Lock()
defer peer.lock.Unlock()
if bv > peer.params.BufLimit {
bv = peer.params.BufLimit
}
sc, ok := peer.pending[reqID]
if !ok {
return
}
delete(peer.pending, reqID)
cc := peer.sumCost - sc
peer.bufEstimate = 0
if bv > cc {
peer.bufEstimate = bv - cc
}
peer.lastTime = mclock.Now()
}
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