routing/payment_lifecycle: use ShardTracker to track shards

We'll let the payment's lifecycle register each shard it's sending with
the ShardTracker, canceling failed shards. This will be the foundation
for correct AMP derivation for each shard we'll send.

routing/shards/shard_tracker.go

@@ -2,6 +2,7 @@ package shards
 
 import (
 	"fmt"
+	"sync"
 
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/record"
@@ -74,6 +75,7 @@ func (s *Shard) AMP() *record.AMP {
 type SimpleShardTracker struct {
 	hash   lntypes.Hash
 	shards map[uint64]lntypes.Hash
+	sync.Mutex
 }
 
 // A compile time check to ensure SimpleShardTracker implements the
@@ -100,7 +102,9 @@ func NewSimpleShardTracker(paymentHash lntypes.Hash,
 // if it ends up not being used by the overall payment, i.e. if the attempt
 // fails.
 func (m *SimpleShardTracker) NewShard(id uint64, _ bool) (PaymentShard, error) {
+	m.Lock()
 	m.shards[id] = m.hash
+	m.Unlock()
 
 	return &Shard{
 		hash: m.hash,
@@ -109,14 +113,19 @@ func (m *SimpleShardTracker) NewShard(id uint64, _ bool) (PaymentShard, error) {
 
 // CancelShard cancel's the shard corresponding to the given attempt ID.
 func (m *SimpleShardTracker) CancelShard(id uint64) error {
+	m.Lock()
 	delete(m.shards, id)
+	m.Unlock()
+
 	return nil
 }
 
 // GetHash retrieves the hash used by the shard of the given attempt ID. This
 // will return an error if the attempt ID is unknown.
 func (m *SimpleShardTracker) GetHash(id uint64) (lntypes.Hash, error) {
+	m.Lock()
 	hash, ok := m.shards[id]
+	m.Unlock()
 	if !ok {
 		return lntypes.Hash{}, fmt.Errorf("hash for attempt id %v "+
 			"not found", id)