refactor(42-background-queues): guard shutdown writes in pkg/metrics

pkg/metrics/store.go

@@ -10,6 +10,7 @@ import (
 	"path/filepath"
 	"strconv"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/rs/zerolog/log"
@@ -92,6 +93,7 @@ type Store struct {
 	stopCh   chan struct{}
 	doneCh   chan struct{}
 	stopOnce sync.Once
+	stopping atomic.Bool
 }
 
 // NewStore creates a new metrics store with the given configuration
@@ -197,9 +199,17 @@ func (s *Store) Write(resourceType, resourceID, metricType string, value float64
 
 // WriteWithTier adds a metric to the write buffer with a specific tier
 func (s *Store) WriteWithTier(resourceType, resourceID, metricType string, value float64, timestamp time.Time, tier Tier) {
+	if s.stopping.Load() {
+		return
+	}
+
 	s.bufferMu.Lock()
 	defer s.bufferMu.Unlock()
 
+	if s.stopping.Load() {
+		return
+	}
+
 	s.buffer = append(s.buffer, bufferedMetric{
 		resourceType: resourceType,
 		resourceID:   resourceID,
@@ -811,6 +821,7 @@ func (s *Store) SetMaxOpenConns(n int) {
 // Close shuts down the store gracefully
 func (s *Store) Close() error {
 	s.stopOnce.Do(func() {
+		s.stopping.Store(true)
 		close(s.stopCh)
 	})
 

pkg/metrics/store_additional_test.go

@@ -111,3 +111,35 @@ func TestStoreGetMetaIntInvalid(t *testing.T) {
 		t.Fatalf("expected getMetaInt to fail for invalid int, got %d", val)
 	}
 }
+
+func TestStoreWriteAfterCloseDoesNotPanic(t *testing.T) {
+	dir := t.TempDir()
+	cfg := DefaultConfig(dir)
+	cfg.DBPath = filepath.Join(dir, "metrics-after-close.db")
+	cfg.WriteBufferSize = 1
+	cfg.FlushInterval = time.Hour
+
+	store, err := NewStore(cfg)
+	if err != nil {
+		t.Fatalf("NewStore returned error: %v", err)
+	}
+
+	if err := store.Close(); err != nil {
+		t.Fatalf("Close returned error: %v", err)
+	}
+
+	var panicked bool
+	func() {
+		defer func() {
+			if recover() != nil {
+				panicked = true
+			}
+		}()
+		store.Write("vm", "v1", "cpu", 1.0, time.Now())
+		store.Flush()
+	}()
+
+	if panicked {
+		t.Fatal("expected writes after close to be ignored without panic")
+	}
+}