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workerpool.go
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workerpool.go
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package fastdns
import (
"log/slog"
"runtime"
"sync"
"time"
)
// workerPool serves incoming connections via a pool of workers
// in FILO order, i.e. the most recently stopped worker will serve the next
// incoming connection.
//
// Such a scheme keeps CPU caches hot (in theory).
type workerPool struct {
// Function for serving server connections.
WorkerFunc func(ctx *udpCtx) error
MaxWorkersCount int
LogAllErrors bool
MaxIdleWorkerDuration time.Duration
Logger *slog.Logger
lock sync.Mutex
workersCount int
mustStop bool
ready []*workerChan
stopCh chan struct{}
workerChanPool sync.Pool
}
type workerItem struct {
ctx *udpCtx
}
type workerChan struct {
lastUseTime time.Time
ch chan workerItem
}
func (wp *workerPool) Start() {
if wp.stopCh != nil {
panic("BUG: workerPool already started")
}
wp.stopCh = make(chan struct{})
stopCh := wp.stopCh
wp.workerChanPool.New = func() interface{} {
return &workerChan{
ch: make(chan workerItem, workerChanCap),
}
}
go func() {
var scratch []*workerChan
for {
wp.clean(&scratch)
select {
case <-stopCh:
return
default:
time.Sleep(wp.getMaxIdleWorkerDuration())
}
}
}()
}
func (wp *workerPool) Stop() {
if wp.stopCh == nil {
panic("BUG: workerPool wasn't started")
}
close(wp.stopCh)
wp.stopCh = nil
// Stop all the workers waiting for incoming connections.
// Do not wait for busy workers - they will stop after
// serving the connection and noticing wp.mustStop = true.
wp.lock.Lock()
ready := wp.ready
for i := range ready {
ready[i].ch <- workerItem{}
ready[i] = nil
}
wp.ready = ready[:0]
wp.mustStop = true
wp.lock.Unlock()
}
func (wp *workerPool) getMaxIdleWorkerDuration() time.Duration {
if wp.MaxIdleWorkerDuration <= 0 {
return 10 * time.Second
}
return wp.MaxIdleWorkerDuration
}
func (wp *workerPool) clean(scratch *[]*workerChan) {
maxIdleWorkerDuration := wp.getMaxIdleWorkerDuration()
// Clean least recently used workers if they didn't serve connections
// for more than maxIdleWorkerDuration.
criticalTime := time.Now().Add(-maxIdleWorkerDuration)
wp.lock.Lock()
ready := wp.ready
n := len(ready)
// Use binary-search algorithm to find out the index of the least recently worker which can be cleaned up.
l, r, mid := 0, n-1, 0
for l <= r {
mid = (l + r) / 2
if criticalTime.After(wp.ready[mid].lastUseTime) {
l = mid + 1
} else {
r = mid - 1
}
}
i := r
if i == -1 {
wp.lock.Unlock()
return
}
*scratch = append((*scratch)[:0], ready[:i+1]...)
m := copy(ready, ready[i+1:])
for i = m; i < n; i++ {
ready[i] = nil
}
wp.ready = ready[:m]
wp.lock.Unlock()
// Notify obsolete workers to stop.
// This notification must be outside the wp.lock, since ch.ch
// may be blocking and may consume a lot of time if many workers
// are located on non-local CPUs.
tmp := *scratch
for i := range tmp {
tmp[i].ch <- workerItem{}
tmp[i] = nil
}
}
func (wp *workerPool) Serve(ctx *udpCtx) bool {
ch := wp.getCh()
if ch == nil {
return false
}
ch.ch <- workerItem{ctx}
return true
}
var workerChanCap = func() int {
// Use blocking workerChan if GOMAXPROCS=1.
// This immediately switches Serve to WorkerFunc, which results
// in higher performance (under go1.5 at least).
if runtime.GOMAXPROCS(0) == 1 {
return 0
}
// Use non-blocking workerChan if GOMAXPROCS>1,
// since otherwise the Serve caller (Acceptor) may lag accepting
// new connections if WorkerFunc is CPU-bound.
return 1
}()
func (wp *workerPool) getCh() *workerChan {
var ch *workerChan
createWorker := false
wp.lock.Lock()
ready := wp.ready
n := len(ready) - 1
if n < 0 {
if wp.workersCount < wp.MaxWorkersCount {
createWorker = true
wp.workersCount++
}
} else {
ch = ready[n]
ready[n] = nil
wp.ready = ready[:n]
}
wp.lock.Unlock()
if ch == nil {
if !createWorker {
return nil
}
vch := wp.workerChanPool.Get()
ch = vch.(*workerChan)
go func() {
wp.workerFunc(ch)
wp.workerChanPool.Put(vch)
}()
}
return ch
}
func (wp *workerPool) release(ch *workerChan) bool {
ch.lastUseTime = time.Now()
wp.lock.Lock()
if wp.mustStop {
wp.lock.Unlock()
return false
}
wp.ready = append(wp.ready, ch)
wp.lock.Unlock()
return true
}
func (wp *workerPool) workerFunc(ch *workerChan) {
var item workerItem
var err error
for item = range ch.ch {
if item.ctx == nil {
break
}
if err = wp.WorkerFunc(item.ctx); err != nil {
if wp.LogAllErrors || !(err == ErrInvalidHeader || err == ErrInvalidQuestion) {
if wp.Logger != nil {
wp.Logger.Error("error when serving connection", "error", err, "local_addr", item.ctx.rw.Conn.LocalAddr(), "remote_addr", item.ctx.rw.AddrPort)
}
}
}
item.ctx = nil
if !wp.release(ch) {
break
}
}
wp.lock.Lock()
wp.workersCount--
wp.lock.Unlock()
}