implemented priority preloading

pkg/fs/preload.go

@@ -4,138 +4,160 @@ package fs
 
 import (
 	"context"
-	"errors"
 	"sync"
 
 	"github.com/go-logr/logr"
 	"golang.org/x/exp/slices"
 )
 
+type queue []*Preload
+
+func (queue) LessReverse(i, j *Preload) bool { return i.Prio > j.Prio }
+
+func (q *queue) Head() (p *Preload) {
+	l := len(*q)
+	if l > 0 {
+		p = (*q)[l-1]
+	}
+	return
+}
+
+func (q *queue) Pop() (p *Preload) {
+	l := len(*q)
+	if l > 0 {
+		p = q.Head()
+		*q = (*q)[:l-1]
+	}
+	return
+}
+
+func (q *queue) Sort() {
+	slices.SortFunc(*q, q.LessReverse)
+}
+
+func (q *queue) Add(ph *PreloadHandler, name string, prio int) {
+	for _, p := range *q {
+		if p.Name == name {
+			p.Prio += prio
+			q.Sort()
+			return
+		}
+	}
+	q.Append(&Preload{Name: name, ph: ph})
+}
+
+func (q *queue) Append(p *Preload) {
+	*q = append(*q, p)
+	q.Sort()
+}
+
+func (q *queue) Remove(name string) {
+	for i, p := range *q {
+		if p.Name == name {
+			p.stop()
+			*q = slices.Delete(*q, i, i+1)
+			q.Sort()
+			return
+		}
+	}
+}
+
 type Preload struct {
+	ph      *PreloadHandler
 	Name    string
 	cancel  func()
+	Prio    int
 	Status  int
 	Running bool
 }
 
-type Preloads []*Preload
-
-func (Preloads) Less(i, j *Preload) bool { return i.Name < j.Name }
+type Preloads []Preload
 
 type PreloadHandler struct {
-	mu    sync.RWMutex
-	log   logr.Logger
-	fs    *FS
-	pm    map[string]*Preload
-	sched chan *Preload
-	fin   chan string
-	pre   int
-	max   int
+	mu  sync.RWMutex
+	log logr.Logger
+	fs  *FS
+	q   queue
+	fin chan string
+	max int
 }
 
 func NewPreloadHandler(ctx context.Context, fs *FS, max int, log logr.Logger) (ph *PreloadHandler) {
-	if max < -1 {
-		max = -1
+	if max <= 0 {
+		max = 1
 	}
 	ph = &PreloadHandler{
-		log:   log,
-		fs:    fs,
-		pm:    make(map[string]*Preload),
-		sched: make(chan *Preload, 1),
-		fin:   make(chan string, 1),
-		max:   max,
+		log: log,
+		fs:  fs,
+		q:   make(queue, 0),
+		fin: make(chan string, 1),
+		max: max,
 	}
-	go ph.preload(ctx)
 	go ph.preloadFinish(ctx)
 	return
 }
 
-func (ph *PreloadHandler) CancelPreload(name string) {
-	ph.mu.Lock()
-	defer ph.mu.Unlock()
-	p, ok := ph.pm[name]
-	if ok {
-		if p.Running {
-			p.cancel()
-		}
-		delete(ph.pm, name)
-	}
+func (ph *PreloadHandler) RemovePreload(name string) {
+	ph.mu.RLock()
+	defer ph.mu.RUnlock()
+	ph.q.Remove(name)
+	ph.schedule()
 }
 
 func (ph *PreloadHandler) Preloads() (ps Preloads) {
 	ph.mu.RLock()
 	defer ph.mu.RUnlock()
-	for _, p := range ph.pm {
-		ps = append(ps, &Preload{
-			Name:    p.Name,
-			Running: p.Running,
-			Status:  ph.fs.CacheStatus(p.Name),
-		})
+	ps = make(Preloads, len(ph.q))
+	for i, v := range ph.q {
+		ps[i] = *v
+		ps[i].Status = ph.fs.CacheStatus(v.Name)
 	}
-	slices.SortFunc(ps, ps.Less)
 	return
 }
 
-func (ph *PreloadHandler) Preload(name string) {
+func (ph *PreloadHandler) Preload(name string, prio int) {
 	ph.mu.Lock()
 	defer ph.mu.Unlock()
+	ph.q.Add(ph, name, prio)
+	ph.schedule()
+}
 
-	p, ok := ph.pm[name]
-	if !ok {
-		p = &Preload{Name: name}
-		ph.pm[name] = p
-		if ph.max == -1 || ph.pre < ph.max {
-			ph.sched <- p
+func (ph *PreloadHandler) schedule() {
+	for i := 0; i < len(ph.q); i++ {
+		if i < ph.max {
+			ph.q[i].start()
+		} else {
+			ph.q[i].stop()
 		}
-		return
 	}
+}
 
+func (p *Preload) start() {
 	if p.Running {
-		ph.log.WithValues("file", name).Error(errors.New("preload is running"), "error starting preload")
-	}
-	return
-}
-
-func (ph *PreloadHandler) nextPreload() {
-	if ph.pre == ph.max {
 		return
 	}
-	for _, p := range ph.pm {
-		if p.Running {
-			continue
-		}
-		ph.sched <- p
+	name := p.Name
+	file, err := p.ph.fs.Open(name)
+	if err != nil {
+		p.ph.log.Error(err, "error staring next preload", "file", name)
 		return
 	}
+	f, ok := file.(*File)
+	if !ok {
+		return
+	}
+	ctx, cancel := context.WithCancel(context.Background())
+	p.Running = true
+	p.cancel = cancel
+	go f.Preload(ctx, func() {
+		p.ph.fin <- name
+	})
 }
 
-func (ph *PreloadHandler) preload(ctx context.Context) {
-	var p *Preload
-	for {
-		select {
-		case <-ctx.Done():
-			return
-		case p = <-ph.sched:
-		}
-		name := p.Name
-		file, err := ph.fs.Open(name)
-		if err != nil {
-			ph.log.Error(err, "error staring next preload", "file", name)
-			return
-		}
-		f, ok := file.(*File)
-		if !ok {
-			continue
-		}
-		ctx, cancel := context.WithCancel(context.Background())
-		ph.mu.Lock()
-		ph.pre++
-		p.Running = true
-		p.cancel = cancel
-		ph.mu.Unlock()
-		go f.Preload(ctx, func() {
-			ph.fin <- name
-		})
+func (p *Preload) stop() {
+	if p.Running {
+		p.cancel()
+		p.Running = false
 	}
 }
 
@@ -147,23 +169,19 @@ func (ph *PreloadHandler) preloadFinish(ctx context.Context) {
 			return
 		case name := <-ph.fin:
 			ph.mu.Lock()
-			delete(ph.pm, name)
-			ph.pre--
-			ph.nextPreload()
+			ph.q.Remove(name)
+			ph.schedule()
 			ph.mu.Unlock()
 		}
 	}
 }
 
 func (ph *PreloadHandler) close() {
-	for _, p := range ph.pm {
-		if p.Running {
-			p.cancel()
-		}
+	for _, p := range ph.q {
+		p.stop()
 	}
 	for {
 		select {
-		case <-ph.sched:
 		case <-ph.fin:
 		default:
 			return