syncthing/lib/connections/limiter.go

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// Copyright (C) 2017 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at http://mozilla.org/MPL/2.0/.
package connections
import (
"fmt"
"io"
"sync/atomic"
"github.com/syncthing/syncthing/lib/config"
"golang.org/x/net/context"
"golang.org/x/time/rate"
)
// limiter manages a read and write rate limit, reacting to config changes
// as appropriate.
type limiter struct {
write *rate.Limiter
read *rate.Limiter
limitsLAN atomicBool
}
const limiterBurstSize = 4 * 128 << 10
func newLimiter(cfg *config.Wrapper) *limiter {
l := &limiter{
write: rate.NewLimiter(rate.Inf, limiterBurstSize),
read: rate.NewLimiter(rate.Inf, limiterBurstSize),
}
cfg.Subscribe(l)
prev := config.Configuration{Options: config.OptionsConfiguration{MaxRecvKbps: -1, MaxSendKbps: -1}}
l.CommitConfiguration(prev, cfg.RawCopy())
return l
}
func (lim *limiter) newReadLimiter(r io.Reader, isLAN bool) io.Reader {
return &limitedReader{reader: r, limiter: lim, isLAN: isLAN}
}
func (lim *limiter) newWriteLimiter(w io.Writer, isLAN bool) io.Writer {
return &limitedWriter{writer: w, limiter: lim, isLAN: isLAN}
}
func (lim *limiter) VerifyConfiguration(from, to config.Configuration) error {
return nil
}
func (lim *limiter) CommitConfiguration(from, to config.Configuration) bool {
if from.Options.MaxRecvKbps == to.Options.MaxRecvKbps &&
from.Options.MaxSendKbps == to.Options.MaxSendKbps &&
from.Options.LimitBandwidthInLan == to.Options.LimitBandwidthInLan {
return true
}
// The rate variables are in KiB/s in the config (despite the camel casing
// of the name). We multiply by 1024 to get bytes/s.
if to.Options.MaxRecvKbps <= 0 {
lim.read.SetLimit(rate.Inf)
} else {
lim.read.SetLimit(1024 * rate.Limit(to.Options.MaxRecvKbps))
}
if to.Options.MaxSendKbps < 0 {
lim.write.SetLimit(rate.Inf)
} else {
lim.write.SetLimit(1024 * rate.Limit(to.Options.MaxSendKbps))
}
lim.limitsLAN.set(to.Options.LimitBandwidthInLan)
sendLimitStr := "is unlimited"
recvLimitStr := "is unlimited"
if to.Options.MaxSendKbps > 0 {
sendLimitStr = fmt.Sprintf("limit is %d KiB/s", to.Options.MaxSendKbps)
}
if to.Options.MaxRecvKbps > 0 {
recvLimitStr = fmt.Sprintf("limit is %d KiB/s", to.Options.MaxRecvKbps)
}
l.Infof("Send rate %s, receive rate %s", sendLimitStr, recvLimitStr)
if to.Options.LimitBandwidthInLan {
l.Infoln("Rate limits apply to LAN connections")
} else {
l.Infoln("Rate limits do not apply to LAN connections")
}
return true
}
func (lim *limiter) String() string {
// required by config.Committer interface
return "connections.limiter"
}
// limitedReader is a rate limited io.Reader
type limitedReader struct {
reader io.Reader
limiter *limiter
isLAN bool
}
func (r *limitedReader) Read(buf []byte) (int, error) {
n, err := r.reader.Read(buf)
if !r.isLAN || r.limiter.limitsLAN.get() {
take(r.limiter.read, n)
}
return n, err
}
// limitedWriter is a rate limited io.Writer
type limitedWriter struct {
writer io.Writer
limiter *limiter
isLAN bool
}
func (w *limitedWriter) Write(buf []byte) (int, error) {
if !w.isLAN || w.limiter.limitsLAN.get() {
take(w.limiter.write, len(buf))
}
return w.writer.Write(buf)
}
// take is a utility function to consume tokens from a rate.Limiter. No call
// to WaitN can be larger than the limiter burst size so we split it up into
// several calls when necessary.
func take(l *rate.Limiter, tokens int) {
if tokens < limiterBurstSize {
// This is the by far more common case so we get it out of the way
// early.
l.WaitN(context.TODO(), tokens)
return
}
for tokens > 0 {
// Consume limiterBurstSize tokens at a time until we're done.
if tokens > limiterBurstSize {
l.WaitN(context.TODO(), limiterBurstSize)
tokens -= limiterBurstSize
} else {
l.WaitN(context.TODO(), tokens)
tokens = 0
}
}
}
type atomicBool int32
func (b *atomicBool) set(v bool) {
if v {
atomic.StoreInt32((*int32)(b), 1)
} else {
atomic.StoreInt32((*int32)(b), 0)
}
}
func (b *atomicBool) get() bool {
return atomic.LoadInt32((*int32)(b)) != 0
}