path: root/les/flowcontrol/control.go

// 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()
}