more code comments, don't bother inserting statuses if timeline not preloaded

internal/cache/timeline/preload.go

@@ -33,10 +33,34 @@ import (
 // - brand-new     = nil (functionally same as 'needs preload')
 type preloader struct{ p atomic.Pointer[any] }
 
-// Check will concurrency-safely check the preload
-// state, and if needed call the provided function.
-// if a preload is in progress, it will wait until complete.
-func (p *preloader) Check(preload func()) {
+// Check will return the current preload state,
+// waiting if a preload is currently in progress.
+func (p *preloader) Check() bool {
+	for {
+		// Get state ptr.
+		ptr := p.p.Load()
+
+		// Check if requires preloading.
+		if ptr == nil || *ptr == false {
+			return false
+		}
+
+		// Check for a preload currently in progress.
+		if wg, _ := (*ptr).(*sync.WaitGroup); wg != nil {
+			wg.Wait()
+			continue
+		}
+
+		// Anything else
+		// means success.
+		return true
+	}
+}
+
+// CheckPreload will safely check the preload state,
+// and if needed call the provided function. if a
+// preload is in progress, it will wait until complete.
+func (p *preloader) CheckPreload(preload func()) {
 	for {
 		// Get state ptr.
 		ptr := p.p.Load()
@@ -95,7 +119,7 @@ func (p *preloader) start(old *any, preload func()) bool {
 
 // done marks state as preloaded,
 // i.e. no more preload required.
-func (p *preloader) done() {
+func (p *preloader) Done() {
 	old := p.p.Swap(new(any))
 	if old == nil { // was brand-new
 		return
@@ -109,7 +133,7 @@ func (p *preloader) done() {
 
 // clear will clear the state, marking a "preload" as required.
 // i.e. next call to Check() will call provided preload func.
-func (p *preloader) clear() {
+func (p *preloader) Clear() {
 	b := false
 	a := any(b)
 	for {

internal/cache/timeline/status.go

@@ -32,6 +32,12 @@ import (
 	"github.com/superseriousbusiness/gotosocial/internal/util/xslices"
 )
 
+// repeatBoostDepth determines the minimum count
+// of statuses after which repeat boosts, or boosts
+// of the original, may appear. This is may not end
+// up *exact*, as small races between insert and the
+// repeatBoost calculation may allow 1 or so extra
+// to sneak in ahead of time. but it mostly works!
 const repeatBoostDepth = 40
 
 // StatusMeta contains minimum viable metadata
@@ -190,14 +196,14 @@ func (t *StatusTimeline) Preload(
 	n int,
 	err error,
 ) {
-	t.preloader.Check(func() {
+	t.preloader.CheckPreload(func() {
 		n, err = t.preload(loadPage, filter)
 		if err != nil {
 			return
 		}
 
 		// Mark preloaded.
-		t.preloader.done()
+		t.preloader.Done()
 	})
 	return
 }
@@ -547,6 +553,13 @@ func loadStatusTimeline(
 // InsertOne allows you to insert a single status into the timeline, with optional prepared API model.
 // The return value indicates whether status should be skipped from streams, e.g. if already boosted recently.
 func (t *StatusTimeline) InsertOne(status *gtsmodel.Status, prepared *apimodel.Status) (skip bool) {
+
+	// If timeline no preloaded, i.e.
+	// no-one using it, don't insert.
+	if !t.preloader.Check() {
+		return false
+	}
+
 	if status.BoostOfID != "" {
 		// Check through top $repeatBoostDepth number of timeline items.
 		for i, value := range t.cache.RangeUnsafe(structr.Desc) {
@@ -718,7 +731,7 @@ func (t *StatusTimeline) Trim() { t.cache.Trim(t.cut, structr.Asc) }
 
 // Clear will mark the entire timeline as requiring preload,
 // which will trigger a clear and reload of the entire thing.
-func (t *StatusTimeline) Clear() { t.preloader.clear() }
+func (t *StatusTimeline) Clear() { t.preloader.Clear() }
 
 // prepareStatuses takes a slice of cached (or, freshly loaded!) StatusMeta{}
 // models, and use given function to return prepared frontend API models.

internal/processing/timeline/timeline.go

@@ -108,29 +108,9 @@ func (p *Processor) getStatusTimeline(
 	// input paging cursor.
 	id.ValidatePage(page)
 
-	// Returned models and page params.
-	var apiStatuses []*apimodel.Status
-	var lo, hi string
-
-	// Pre-prepared filter function that just ensures we
-	// don't end up serving multiple copies of the same boost.
-	prepare := func(status *gtsmodel.Status) (*apimodel.Status, error) {
-		apiStatus, err := p.converter.StatusToAPIStatus(ctx,
-			status,
-			requester,
-			filterCtx,
-			filters,
-			mutes,
-		)
-		if err != nil && !errors.Is(err, statusfilter.ErrHideStatus) {
-			return nil, err
-		}
-		return apiStatus, nil
-	}
-
 	// Load status page via timeline cache, also
 	// getting lo, hi values for next, prev pages.
-	apiStatuses, lo, hi, err = timeline.Load(ctx,
+	apiStatuses, lo, hi, err := timeline.Load(ctx,
 
 		// Status page
 		// to load.
@@ -145,13 +125,24 @@ func (p *Processor) getStatusTimeline(
 			return p.state.DB.GetStatusesByIDs(ctx, ids)
 		},
 
-		// Filtering function,
-		// i.e. filter before caching.
+		// Call provided status
+		// filtering function.
 		filter,
 
-		// Frontend API model
-		// preparation function.
-		prepare,
+		// Frontend API model preparation function.
+		func(status *gtsmodel.Status) (*apimodel.Status, error) {
+			apiStatus, err := p.converter.StatusToAPIStatus(ctx,
+				status,
+				requester,
+				filterCtx,
+				filters,
+				mutes,
+			)
+			if err != nil && !errors.Is(err, statusfilter.ErrHideStatus) {
+				return nil, err
+			}
+			return apiStatus, nil
+		},
 	)
 
 	if err != nil {