[#1284] writecache: Allow to seal writecache async

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

pkg/local_object_storage/shard/writecache.go

@@ -4,12 +4,24 @@ import (
 	"context"
 	"errors"
 
+	"git.frostfs.info/TrueCloudLab/frostfs-node/internal/logs"
 	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/writecache"
 	"git.frostfs.info/TrueCloudLab/frostfs-observability/tracing"
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/trace"
+	"go.uber.org/zap"
 )
 
+var (
+	dummyCancel          = &writecacheSealCanceler{cancel: func() {}}
+	notInitializedCancel = &writecacheSealCanceler{cancel: func() {}}
+	errWriteCacheSealing = errors.New("writecache is already sealing or shard is not initialized")
+)
+
+type writecacheSealCanceler struct {
+	cancel context.CancelFunc
+}
+
 // FlushWriteCachePrm represents parameters of a `FlushWriteCache` operation.
 type FlushWriteCachePrm struct {
 	ignoreErrors bool
@@ -60,6 +72,7 @@ func (s *Shard) FlushWriteCache(ctx context.Context, p FlushWriteCachePrm) error
 
 type SealWriteCachePrm struct {
 	IgnoreErrors bool
+	Async        bool
 	RestoreMode  bool
 	Shrink       bool
 }
@@ -78,15 +91,52 @@ func (s *Shard) SealWriteCache(ctx context.Context, p SealWriteCachePrm) error {
 		return errWriteCacheDisabled
 	}
 
+	if p.Async {
+		ctx = context.WithoutCancel(ctx)
+	}
+	ctx, cancel := context.WithCancel(ctx)
+	canceler := &writecacheSealCanceler{cancel: cancel}
+	if !s.writecacheSealCancel.CompareAndSwap(dummyCancel, canceler) {
+		return errWriteCacheSealing
+	}
 	s.m.RLock()
-	defer s.m.RUnlock()
+	cleanup := func() {
+		s.m.RUnlock()
+		s.writecacheSealCancel.Store(dummyCancel)
+	}
 
 	if s.info.Mode.ReadOnly() {
+		cleanup()
 		return ErrReadOnlyMode
 	}
 	if s.info.Mode.NoMetabase() {
+		cleanup()
 		return ErrDegradedMode
 	}
 
-	return s.writeCache.Seal(ctx, writecache.SealPrm{IgnoreErrors: p.IgnoreErrors, RestoreMode: p.RestoreMode, Shrink: p.Shrink})
+	if !p.Async {
+		defer cleanup()
+	}
+	prm := writecache.SealPrm{IgnoreErrors: p.IgnoreErrors, RestoreMode: p.RestoreMode, Shrink: p.Shrink}
+	if p.Async {
+		started := make(chan struct{})
+		go func() {
+			close(started)
+			defer cleanup()
+
+			s.log.Info(logs.StartedWritecacheSealAsync)
+			if err := s.writeCache.Seal(ctx, prm); err != nil {
+				s.log.Warn(logs.FailedToSealWritecacheAsync, zap.Error(err))
+				return
+			}
+			s.log.Info(logs.WritecacheSealCompletedAsync)
+		}()
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case <-started:
+			return nil
+		}
+	}
+	return s.writeCache.Seal(ctx, prm)
 }