batch: dont expose kvdb.RwTx in batch.SchedulerOptions

Currently, a few of the graph KVStore methods take the
`batch.SchedulerOptions` param. This is only used to set the LazyAdd
option. A SchedulerOption is a functional option that takes a
`batch.Request` which has bolt-specific fields in it. This commit
restructures things a bit such that the `batch.Request` type is no
longer part of the `batch.SchedulerOptions` - this will make it easier
to implement the graph store with a different DB backend.

batch/interface.go

@@ -5,6 +5,9 @@ import "github.com/lightningnetwork/lnd/kvdb"
 // Request defines an operation that can be batched into a single bbolt
 // transaction.
 type Request struct {
+	// Opts holds various configuration options for a scheduled request.
+	Opts *SchedulerOptions
+
 	// Reset is called before each invocation of Update and is used to clear
 	// any possible modifications to local state as a result of previous
 	// calls to Update that were not committed due to a concurrent batch
@@ -25,22 +28,45 @@ type Request struct {
 	//
 	// NOTE: This field is optional.
 	OnCommit func(commitErr error) error
+}
 
+// SchedulerOptions holds various configuration options for a scheduled request.
+type SchedulerOptions struct {
 	// lazy should be true if we don't have to immediately execute this
 	// request when it comes in. This means that it can be scheduled later,
 	// allowing larger batches.
 	lazy bool
 }
 
+// NewDefaultSchedulerOpts returns a new SchedulerOptions with default values.
+func NewDefaultSchedulerOpts() *SchedulerOptions {
+	return &SchedulerOptions{
+		lazy: false,
+	}
+}
+
+// NewSchedulerOptions returns a new SchedulerOptions with the given options
+// applied on top of the default options.
+func NewSchedulerOptions(options ...SchedulerOption) *SchedulerOptions {
+	opts := NewDefaultSchedulerOpts()
+	for _, o := range options {
+		o(opts)
+	}
+
+	return opts
+}
+
 // SchedulerOption is a type that can be used to supply options to a scheduled
 // request.
-type SchedulerOption func(r *Request)
+type SchedulerOption func(*SchedulerOptions)
 
 // LazyAdd will make the request be executed lazily, added to the next batch to
 // reduce db contention.
+//
+// NOTE: This is currently a no-op for any DB backend other than bbolt.
 func LazyAdd() SchedulerOption {
-	return func(r *Request) {
-		r.lazy = true
+	return func(opts *SchedulerOptions) {
+		opts.lazy = true
 	}
 }
 

batch/scheduler.go

@@ -43,6 +43,10 @@ func NewTimeScheduler(db kvdb.Backend, locker sync.Locker,
 //
 // NOTE: Part of the Scheduler interface.
 func (s *TimeScheduler) Execute(r *Request) error {
+	if r.Opts == nil {
+		r.Opts = NewDefaultSchedulerOpts()
+	}
+
 	req := request{
 		Request: r,
 		errChan: make(chan error, 1),
@@ -62,7 +66,7 @@ func (s *TimeScheduler) Execute(r *Request) error {
 	s.b.reqs = append(s.b.reqs, &req)
 
 	// If this is a non-lazy request, we'll execute the batch immediately.
-	if !r.lazy {
+	if !r.Opts.lazy {
 		go s.b.trigger()
 	}