Implement ticketed chunk lifecycle

internal/world/cache_tickets_test.go

@@ -0,0 +1,78 @@
+package world
+
+import (
+	"context"
+	"errors"
+	"testing"
+)
+
+func TestTicketPinsChunkUntilRelease(t *testing.T) {
+	cache := NewCacheWithLimit(-1, func(cx, cz int32) *Chunk {
+		return NewChunk(cx, cz, BiomePlains)
+	}, nil, 2)
+	tickets := cache.NewTicketSet()
+	tickets.Replace([]ChunkPos{{X: 0, Z: 0}}, nil)
+	for x := int32(0); x < 4; x++ {
+		if _, err := cache.FrameErr(x, 0); err != nil {
+			t.Fatal(err)
+		}
+	}
+	if !hasChunk(cache, 0, 0) {
+		t.Fatal("ticketed chunk was evicted")
+	}
+	if got := cache.Stats().Tickets; got != 1 {
+		t.Fatalf("ticket count = %d, want 1", got)
+	}
+
+	tickets.Close()
+	if got := cache.Stats(); got.Tickets != 0 || got.Chunks > 2 {
+		t.Fatalf("after release stats = %+v, want no tickets and <=2 chunks", got)
+	}
+}
+
+func TestOverlappingTicketSetsRequireFinalRelease(t *testing.T) {
+	cache := NewCacheWithLimit(-1, func(cx, cz int32) *Chunk {
+		return NewChunk(cx, cz, BiomePlains)
+	}, nil, 1)
+	first, second := cache.NewTicketSet(), cache.NewTicketSet()
+	pos := []ChunkPos{{X: 0, Z: 0}}
+	first.Replace(pos, nil)
+	second.Replace(nil, pos)
+	if _, err := cache.FrameErr(0, 0); err != nil {
+		t.Fatal(err)
+	}
+	first.Close()
+	if got := cache.Stats().Tickets; got != 1 {
+		t.Fatalf("tickets after first close = %d, want 1", got)
+	}
+	if _, err := cache.FrameErr(1, 0); err != nil {
+		t.Fatal(err)
+	}
+	if !hasChunk(cache, 0, 0) {
+		t.Fatal("chunk was evicted while second owner still held it")
+	}
+
+	second.Close()
+	second.Close() // idempotent
+	if got := cache.Stats(); got.Tickets != 0 || got.Chunks > 1 {
+		t.Fatalf("after final close stats = %+v", got)
+	}
+}
+
+func TestFrameAdmissionCanBeCancelled(t *testing.T) {
+	cache := NewCache(-1, func(cx, cz int32) *Chunk {
+		return NewChunk(cx, cz, BiomePlains)
+	})
+	for i := 0; i < cap(cache.frameSlots); i++ {
+		cache.frameSlots <- struct{}{}
+	}
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	_, err := cache.FrameErrContext(ctx, 0, 0)
+	if !errors.Is(err, context.Canceled) {
+		t.Fatalf("FrameErrContext error = %v, want context.Canceled", err)
+	}
+	for i := 0; i < cap(cache.frameSlots); i++ {
+		<-cache.frameSlots
+	}
+}