multi: replace manual CAS with sync.Once in component start/stop

This guarantees callers that the method will not return until it
has executed completely at least once.

autopilot/agent.go

@@ -6,7 +6,6 @@ import (
 	"math/rand"
 	"net"
 	"sync"
-	"sync/atomic"
 	"time"
 
 	"github.com/btcsuite/btcd/btcec"
@@ -105,9 +104,8 @@ func (c channelState) ConnectedNodes() map[NodeID]struct{} {
 //
 // TODO(roasbeef): prob re-word
 type Agent struct {
-	// Only to be used atomically.
-	started uint32
-	stopped uint32
+	started sync.Once
+	stopped sync.Once
 
 	// cfg houses the configuration state of the Ant.
 	cfg Config
@@ -197,10 +195,14 @@ func New(cfg Config, initialState []Channel) (*Agent, error) {
 // Start starts the agent along with any goroutines it needs to perform its
 // normal duties.
 func (a *Agent) Start() error {
-	if !atomic.CompareAndSwapUint32(&a.started, 0, 1) {
-		return nil
-	}
+	var err error
+	a.started.Do(func() {
+		err = a.start()
+	})
+	return err
+}
 
+func (a *Agent) start() error {
 	rand.Seed(time.Now().Unix())
 	log.Infof("Autopilot Agent starting")
 
@@ -213,10 +215,14 @@ func (a *Agent) Start() error {
 // Stop signals the Agent to gracefully shutdown. This function will block
 // until all goroutines have exited.
 func (a *Agent) Stop() error {
-	if !atomic.CompareAndSwapUint32(&a.stopped, 0, 1) {
-		return nil
-	}
+	var err error
+	a.stopped.Do(func() {
+		err = a.stop()
+	})
+	return err
+}
 
+func (a *Agent) stop() error {
 	log.Infof("Autopilot Agent stopping")
 
 	close(a.quit)

autopilot/manager.go

@@ -3,7 +3,6 @@ package autopilot
 import (
 	"fmt"
 	"sync"
-	"sync/atomic"
 
 	"github.com/btcsuite/btcd/btcec"
 	"github.com/lightningnetwork/lnd/lnwallet"
@@ -40,8 +39,8 @@ type ManagerCfg struct {
 // It implements the autopilot grpc service, which is used to get data about
 // the running autopilot, and give it relevant information.
 type Manager struct {
-	started uint32 // To be used atomically.
-	stopped uint32 // To be used atomically.
+	started sync.Once
+	stopped sync.Once
 
 	cfg *ManagerCfg
 
@@ -64,27 +63,21 @@ func NewManager(cfg *ManagerCfg) (*Manager, error) {
 
 // Start starts the Manager.
 func (m *Manager) Start() error {
-	if !atomic.CompareAndSwapUint32(&m.started, 0, 1) {
-		return nil
-	}
-
+	m.started.Do(func() {})
 	return nil
 }
 
 // Stop stops the Manager. If an autopilot agent is active, it will also be
 // stopped.
 func (m *Manager) Stop() error {
-	if !atomic.CompareAndSwapUint32(&m.stopped, 0, 1) {
-		return nil
-	}
-
-	if err := m.StopAgent(); err != nil {
-		log.Errorf("Unable to stop pilot: %v", err)
-	}
-
-	close(m.quit)
-	m.wg.Wait()
+	m.stopped.Do(func() {
+		if err := m.StopAgent(); err != nil {
+			log.Errorf("Unable to stop pilot: %v", err)
+		}
 
+		close(m.quit)
+		m.wg.Wait()
+	})
 	return nil
 }
 

breacharbiter.go

@@ -7,7 +7,6 @@ import (
 	"fmt"
 	"io"
 	"sync"
-	"sync/atomic"
 
 	"github.com/btcsuite/btcd/blockchain"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
@@ -118,8 +117,8 @@ type BreachConfig struct {
 // counterparties.
 // TODO(roasbeef): closures in config for subsystem pointers to decouple?
 type breachArbiter struct {
-	started uint32 // To be used atomically.
-	stopped uint32 // To be used atomically.
+	started sync.Once
+	stopped sync.Once
 
 	cfg *BreachConfig
 
@@ -140,10 +139,14 @@ func newBreachArbiter(cfg *BreachConfig) *breachArbiter {
 // Start is an idempotent method that officially starts the breachArbiter along
 // with all other goroutines it needs to perform its functions.
 func (b *breachArbiter) Start() error {
-	if !atomic.CompareAndSwapUint32(&b.started, 0, 1) {
-		return nil
-	}
+	var err error
+	b.started.Do(func() {
+		err = b.start()
+	})
+	return err
+}
 
+func (b *breachArbiter) start() error {
 	brarLog.Tracef("Starting breach arbiter")
 
 	// Load all retributions currently persisted in the retribution store.
@@ -226,15 +229,12 @@ func (b *breachArbiter) Start() error {
 // graceful shutdown. This function will block until all goroutines spawned by
 // the breachArbiter have gracefully exited.
 func (b *breachArbiter) Stop() error {
-	if !atomic.CompareAndSwapUint32(&b.stopped, 0, 1) {
-		return nil
-	}
-
-	brarLog.Infof("Breach arbiter shutting down")
-
-	close(b.quit)
-	b.wg.Wait()
+	b.stopped.Do(func() {
+		brarLog.Infof("Breach arbiter shutting down")
 
+		close(b.quit)
+		b.wg.Wait()
+	})
 	return nil
 }
 

chanbackup/pubsub.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"net"
 	"sync"
-	"sync/atomic"
 
 	"github.com/btcsuite/btcd/wire"
 	"github.com/lightningnetwork/lnd/channeldb"
@@ -79,8 +78,8 @@ type ChannelNotifier interface {
 //
 // TODO(roasbeef): better name lol
 type SubSwapper struct {
-	started uint32
-	stopped uint32
+	started sync.Once
+	stopped sync.Once
 
 	// backupState are the set of SCBs for all open channels we know of.
 	backupState map[wire.OutPoint]Single
@@ -135,29 +134,23 @@ func NewSubSwapper(startingChans []Single, chanNotifier ChannelNotifier,
 
 // Start starts the chanbackup.SubSwapper.
 func (s *SubSwapper) Start() error {
-	if !atomic.CompareAndSwapUint32(&s.started, 0, 1) {
-		return nil
-	}
-
-	log.Infof("Starting chanbackup.SubSwapper")
-
-	s.wg.Add(1)
-	go s.backupUpdater()
+	s.started.Do(func() {
+		log.Infof("Starting chanbackup.SubSwapper")
 
+		s.wg.Add(1)
+		go s.backupUpdater()
+	})
 	return nil
 }
 
 // Stop signals the SubSwapper to being a graceful shutdown.
 func (s *SubSwapper) Stop() error {
-	if !atomic.CompareAndSwapUint32(&s.stopped, 0, 1) {
-		return nil
-	}
-
-	log.Infof("Stopping chanbackup.SubSwapper")
-
-	close(s.quit)
-	s.wg.Wait()
+	s.stopped.Do(func() {
+		log.Infof("Stopping chanbackup.SubSwapper")
 
+		close(s.quit)
+		s.wg.Wait()
+	})
 	return nil
 }
 

fundingmanager.go

@@ -5,7 +5,6 @@ import (
 	"encoding/binary"
 	"fmt"
 	"sync"
-	"sync/atomic"
 	"time"
 
 	"github.com/btcsuite/btcd/btcec"
@@ -353,9 +352,8 @@ type fundingConfig struct {
 // controls between the wallet and remote peers are enforced via the funding
 // manager.
 type fundingManager struct {
-	// MUST be used atomically.
-	started int32
-	stopped int32
+	started sync.Once
+	stopped sync.Once
 
 	// cfg is a copy of the configuration struct that the FundingManager
 	// was initialized with.
@@ -471,10 +469,14 @@ func newFundingManager(cfg fundingConfig) (*fundingManager, error) {
 // Start launches all helper goroutines required for handling requests sent
 // to the funding manager.
 func (f *fundingManager) Start() error {
-	if atomic.AddInt32(&f.started, 1) != 1 { // TODO(roasbeef): CAS instead
-		return nil
-	}
+	var err error
+	f.started.Do(func() {
+		err = f.start()
+	})
+	return err
+}
 
+func (f *fundingManager) start() error {
 	fndgLog.Tracef("Funding manager running")
 
 	// Upon restart, the Funding Manager will check the database to load any
@@ -710,10 +712,14 @@ func (f *fundingManager) Start() error {
 // Stop signals all helper goroutines to execute a graceful shutdown. This
 // method will block until all goroutines have exited.
 func (f *fundingManager) Stop() error {
-	if atomic.AddInt32(&f.stopped, 1) != 1 {
-		return nil
-	}
+	var err error
+	f.stopped.Do(func() {
+		err = f.stop()
+	})
+	return err
+}
 
+func (f *fundingManager) stop() error {
 	fndgLog.Infof("Funding manager shutting down")
 
 	close(f.quit)