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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
assignedRequest uint64 // when != 0, only the request with the given ID can be sent to this peer
assignToken chan struct{} // send to this channel before assigning, read from it after deassigning
lock sync.RWMutex
}
func NewServerNode(params *ServerParams) *ServerNode {
return &ServerNode{
bufEstimate: params.BufLimit,
lastTime: mclock.Now(),
params: params,
pending: make(map[uint64]uint64),
assignToken: make(chan struct{}, 1),
}
}
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 * 200
func (peer *ServerNode) canSend(maxCost uint64) time.Duration {
maxCost += uint64(safetyMargin) * peer.params.MinRecharge / uint64(fcTimeConst)
if maxCost > peer.params.BufLimit {
maxCost = peer.params.BufLimit
}
if peer.bufEstimate >= maxCost {
return 0
}
return time.Duration((maxCost - peer.bufEstimate) * uint64(fcTimeConst) / peer.params.MinRecharge)
}
// CanSend returns the minimum waiting time required before sending a request
// with the given maximum estimated cost
func (peer *ServerNode) CanSend(maxCost uint64) time.Duration {
peer.lock.RLock()
defer peer.lock.RUnlock()
return peer.canSend(maxCost)
}
// AssignRequest tries to assign the server node to the given request, guaranteeing
// that once it returns true, no request will be sent to the node before this one
func (peer *ServerNode) AssignRequest(reqID uint64) bool {
select {
case peer.assignToken <- struct{}{}:
default:
return false
}
peer.lock.Lock()
peer.assignedRequest = reqID
peer.lock.Unlock()
return true
}
// MustAssignRequest waits until the node can be assigned to the given request.
// It is always guaranteed that assignments are released in a short amount of time.
func (peer *ServerNode) MustAssignRequest(reqID uint64) {
peer.assignToken <- struct{}{}
peer.lock.Lock()
peer.assignedRequest = reqID
peer.lock.Unlock()
}
// DeassignRequest releases a request assignment in case the planned request
// is not being sent.
func (peer *ServerNode) DeassignRequest(reqID uint64) {
peer.lock.Lock()
if peer.assignedRequest == reqID {
peer.assignedRequest = 0
<-peer.assignToken
}
peer.lock.Unlock()
}
// IsAssigned returns true if the server node has already been assigned to a request
// (note that this function returning false does not guarantee that you can assign a request
// immediately afterwards, its only purpose is to help peer selection)
func (peer *ServerNode) IsAssigned() bool {
peer.lock.RLock()
locked := peer.assignedRequest != 0
peer.lock.RUnlock()
return locked
}
// blocks until request can be sent
func (peer *ServerNode) SendRequest(reqID, maxCost uint64) {
peer.lock.Lock()
defer peer.lock.Unlock()
if peer.assignedRequest != reqID {
peer.lock.Unlock()
peer.MustAssignRequest(reqID)
peer.lock.Lock()
}
peer.recalcBLE(mclock.Now())
wait := peer.canSend(maxCost)
for wait > 0 {
peer.lock.Unlock()
time.Sleep(wait)
peer.lock.Lock()
peer.recalcBLE(mclock.Now())
wait = peer.canSend(maxCost)
}
peer.assignedRequest = 0
<-peer.assignToken
peer.bufEstimate -= maxCost
peer.sumCost += maxCost
if reqID >= 0 {
peer.pending[reqID] = peer.sumCost
}
}
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)
peer.bufEstimate = bv - (peer.sumCost - sc)
peer.lastTime = mclock.Now()
}
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