multimutex: remove HashMutex, make Mutex type a type param

In this commit, we eliminate some code duplication by removing the old
`HashMutex` struct as it just duplicates all the code with a different
type (uint64 and hash). We then make the main Mutex struct take a type
param, so the key can be parametrized when the struct is instantiated.

blockcache/blockcache.go

@@ -14,7 +14,7 @@ import (
 // BlockCache is an lru cache for blocks.
 type BlockCache struct {
 	Cache     *lru.Cache[wire.InvVect, *neutrino.CacheableBlock]
-	HashMutex *multimutex.HashMutex
+	HashMutex *multimutex.Mutex[lntypes.Hash]
 }
 
 // NewBlockCache creates a new BlockCache with the given maximum capacity.
@@ -23,7 +23,7 @@ func NewBlockCache(capacity uint64) *BlockCache {
 		Cache: lru.NewCache[wire.InvVect, *neutrino.CacheableBlock](
 			capacity,
 		),
-		HashMutex: multimutex.NewHashMutex(),
+		HashMutex: multimutex.NewMutex[lntypes.Hash](),
 	}
 }
 

discovery/gossiper.go

@@ -450,7 +450,7 @@ type AuthenticatedGossiper struct {
 	// goroutine per channel ID. This is done to ensure that when
 	// the gossiper is handling an announcement, the db state stays
 	// consistent between when the DB is first read until it's written.
-	channelMtx *multimutex.Mutex
+	channelMtx *multimutex.Mutex[uint64]
 
 	recentRejects *lru.Cache[rejectCacheKey, *cachedReject]
 
@@ -496,7 +496,7 @@ func New(cfg Config, selfKeyDesc *keychain.KeyDescriptor) *AuthenticatedGossiper
 		prematureChannelUpdates: lru.NewCache[uint64, *cachedNetworkMsg]( //nolint: lll
 			maxPrematureUpdates,
 		),
-		channelMtx: multimutex.NewMutex(),
+		channelMtx: multimutex.NewMutex[uint64](),
 		recentRejects: lru.NewCache[rejectCacheKey, *cachedReject](
 			maxRejectedUpdates,
 		),

htlcswitch/payment_result.go

@@ -93,14 +93,14 @@ type networkResultStore struct {
 	// paymentIDMtx is a multimutex used to make sure the database and
 	// result subscribers map is consistent for each payment ID in case of
 	// concurrent callers.
-	paymentIDMtx *multimutex.Mutex
+	paymentIDMtx *multimutex.Mutex[uint64]
 }
 
 func newNetworkResultStore(db kvdb.Backend) *networkResultStore {
 	return &networkResultStore{
 		backend:      db,
 		results:      make(map[uint64][]chan *networkResult),
-		paymentIDMtx: multimutex.NewMutex(),
+		paymentIDMtx: multimutex.NewMutex[uint64](),
 	}
 }
 

multimutex/hash_mutex.go

@@ -1,90 +0,0 @@
-package multimutex
-
-import (
-	"fmt"
-	"sync"
-
-	"github.com/lightningnetwork/lnd/lntypes"
-)
-
-// HashMutex is a struct that keeps track of a set of mutexes with a given hash.
-// It can be used for making sure only one goroutine gets given the mutex per
-// hash.
-type HashMutex struct {
-	// mutexes is a map of hashes to a cntMutex. The cntMutex for
-	// a given hash will hold the mutex to be used by all
-	// callers requesting access for the hash, in addition to
-	// the count of callers.
-	mutexes map[lntypes.Hash]*cntMutex
-
-	// mapMtx is used to give synchronize concurrent access
-	// to the mutexes map.
-	mapMtx sync.Mutex
-}
-
-// NewHashMutex creates a new Mutex.
-func NewHashMutex() *HashMutex {
-	return &HashMutex{
-		mutexes: make(map[lntypes.Hash]*cntMutex),
-	}
-}
-
-// Lock locks the mutex by the given hash. If the mutex is already
-// locked by this hash, Lock blocks until the mutex is available.
-func (c *HashMutex) Lock(hash lntypes.Hash) {
-	c.mapMtx.Lock()
-	mtx, ok := c.mutexes[hash]
-	if ok {
-		// If the mutex already existed in the map, we
-		// increment its counter, to indicate that there
-		// now is one more goroutine waiting for it.
-		mtx.cnt++
-	} else {
-		// If it was not in the map, it means no other
-		// goroutine has locked the mutex for this hash,
-		// and we can create a new mutex with count 1
-		// and add it to the map.
-		mtx = &cntMutex{
-			cnt: 1,
-		}
-		c.mutexes[hash] = mtx
-	}
-	c.mapMtx.Unlock()
-
-	// Acquire the mutex for this hash.
-	mtx.Lock()
-}
-
-// Unlock unlocks the mutex by the given hash. It is a run-time
-// error if the mutex is not locked by the hash on entry to Unlock.
-func (c *HashMutex) Unlock(hash lntypes.Hash) {
-	// Since we are done with all the work for this
-	// update, we update the map to reflect that.
-	c.mapMtx.Lock()
-
-	mtx, ok := c.mutexes[hash]
-	if !ok {
-		// The mutex not existing in the map means
-		// an unlock for an hash not currently locked
-		// was attempted.
-		panic(fmt.Sprintf("double unlock for hash %v",
-			hash))
-	}
-
-	// Decrement the counter. If the count goes to
-	// zero, it means this caller was the last one
-	// to wait for the mutex, and we can delete it
-	// from the map. We can do this safely since we
-	// are under the mapMtx, meaning that all other
-	// goroutines waiting for the mutex already
-	// have incremented it, or will create a new
-	// mutex when they get the mapMtx.
-	mtx.cnt--
-	if mtx.cnt == 0 {
-		delete(c.mutexes, hash)
-	}
-	c.mapMtx.Unlock()
-
-	// Unlock the mutex for this hash.
-	mtx.Unlock()
-}

multimutex/multimutex.go

@@ -5,51 +5,48 @@ import (
 	"sync"
 )
 
-// cntMutex is a struct that wraps a counter and a mutex, and is used
-// to keep track of the number of goroutines waiting for access to the
+// cntMutex is a struct that wraps a counter and a mutex, and is used to keep
+// track of the number of goroutines waiting for access to the
 // mutex, such that we can forget about it when the counter is zero.
 type cntMutex struct {
 	cnt int
 	sync.Mutex
 }
 
-// Mutex is a struct that keeps track of a set of mutexes with
-// a given ID. It can be used for making sure only one goroutine
-// gets given the mutex per ID.
-type Mutex struct {
-	// mutexes is a map of IDs to a cntMutex. The cntMutex for
-	// a given ID will hold the mutex to be used by all
-	// callers requesting access for the ID, in addition to
-	// the count of callers.
-	mutexes map[uint64]*cntMutex
+// Mutex is a struct that keeps track of a set of mutexes with a given ID. It
+// can be used for making sure only one goroutine gets given the mutex per ID.
+type Mutex[T comparable] struct {
+	// mutexes is a map of IDs to a cntMutex. The cntMutex for a given ID
+	// will hold the mutex to be used by all callers requesting access for
+	// the ID, in addition to the count of callers.
+	mutexes map[T]*cntMutex
 
-	// mapMtx is used to give synchronize concurrent access
-	// to the mutexes map.
+	// mapMtx is used to give synchronize concurrent access to the mutexes
+	// map.
 	mapMtx sync.Mutex
 }
 
 // NewMutex creates a new Mutex.
-func NewMutex() *Mutex {
-	return &Mutex{
-		mutexes: make(map[uint64]*cntMutex),
+func NewMutex[T comparable]() *Mutex[T] {
+	return &Mutex[T]{
+		mutexes: make(map[T]*cntMutex),
 	}
 }
 
-// Lock locks the mutex by the given ID. If the mutex is already
-// locked by this ID, Lock blocks until the mutex is available.
-func (c *Mutex) Lock(id uint64) {
+// Lock locks the mutex by the given ID. If the mutex is already locked by this
+// ID, Lock blocks until the mutex is available.
+func (c *Mutex[T]) Lock(id T) {
 	c.mapMtx.Lock()
 	mtx, ok := c.mutexes[id]
 	if ok {
-		// If the mutex already existed in the map, we
-		// increment its counter, to indicate that there
-		// now is one more goroutine waiting for it.
+		// If the mutex already existed in the map, we increment its
+		// counter, to indicate that there now is one more goroutine
+		// waiting for it.
 		mtx.cnt++
 	} else {
-		// If it was not in the map, it means no other
-		// goroutine has locked the mutex for this ID,
-		// and we can create a new mutex with count 1
-		// and add it to the map.
+		// If it was not in the map, it means no other goroutine has
+		// locked the mutex for this ID, and we can create a new mutex
+		// with count 1 and add it to the map.
 		mtx = &cntMutex{
 			cnt: 1,
 		}
@@ -61,30 +58,26 @@ func (c *Mutex) Lock(id uint64) {
 	mtx.Lock()
 }
 
-// Unlock unlocks the mutex by the given ID. It is a run-time
-// error if the mutex is not locked by the ID on entry to Unlock.
-func (c *Mutex) Unlock(id uint64) {
-	// Since we are done with all the work for this
-	// update, we update the map to reflect that.
+// Unlock unlocks the mutex by the given ID. It is a run-time error if the
+// mutex is not locked by the ID on entry to Unlock.
+func (c *Mutex[T]) Unlock(id T) {
+	// Since we are done with all the work for this update, we update the
+	// map to reflect that.
 	c.mapMtx.Lock()
 
 	mtx, ok := c.mutexes[id]
 	if !ok {
-		// The mutex not existing in the map means
-		// an unlock for an ID not currently locked
-		// was attempted.
+		// The mutex not existing in the map means an unlock for an ID
+		// not currently locked was attempted.
 		panic(fmt.Sprintf("double unlock for id %v",
 			id))
 	}
 
-	// Decrement the counter. If the count goes to
-	// zero, it means this caller was the last one
-	// to wait for the mutex, and we can delete it
-	// from the map. We can do this safely since we
-	// are under the mapMtx, meaning that all other
-	// goroutines waiting for the mutex already
-	// have incremented it, or will create a new
-	// mutex when they get the mapMtx.
+	// Decrement the counter. If the count goes to zero, it means this
+	// caller was the last one to wait for the mutex, and we can delete it
+	// from the map. We can do this safely since we are under the mapMtx,
+	// meaning that all other goroutines waiting for the mutex already have
+	// incremented it, or will create a new mutex when they get the mapMtx.
 	mtx.cnt--
 	if mtx.cnt == 0 {
 		delete(c.mutexes, id)

routing/control_tower.go

@@ -132,7 +132,7 @@ type controlTower struct {
 	// paymentsMtx provides synchronization on the payment level to ensure
 	// that no race conditions occur in between updating the database and
 	// sending a notification.
-	paymentsMtx *multimutex.HashMutex
+	paymentsMtx *multimutex.Mutex[lntypes.Hash]
 }
 
 // NewControlTower creates a new instance of the controlTower.
@@ -143,7 +143,7 @@ func NewControlTower(db *channeldb.PaymentControl) ControlTower {
 			map[uint64]*controlTowerSubscriberImpl,
 		),
 		subscribers: make(map[lntypes.Hash][]*controlTowerSubscriberImpl),
-		paymentsMtx: multimutex.NewHashMutex(),
+		paymentsMtx: multimutex.NewMutex[lntypes.Hash](),
 	}
 }
 

routing/router.go

@@ -442,7 +442,7 @@ type ChannelRouter struct {
 	// channelEdgeMtx is a mutex we use to make sure we process only one
 	// ChannelEdgePolicy at a time for a given channelID, to ensure
 	// consistency between the various database accesses.
-	channelEdgeMtx *multimutex.Mutex
+	channelEdgeMtx *multimutex.Mutex[uint64]
 
 	// statTicker is a resumable ticker that logs the router's progress as
 	// it discovers channels or receives updates.
@@ -480,7 +480,7 @@ func New(cfg Config) (*ChannelRouter, error) {
 		networkUpdates:    make(chan *routingMsg),
 		topologyClients:   &lnutils.SyncMap[uint64, *topologyClient]{},
 		ntfnClientUpdates: make(chan *topologyClientUpdate),
-		channelEdgeMtx:    multimutex.NewMutex(),
+		channelEdgeMtx:    multimutex.NewMutex[uint64](),
 		selfNode:          selfNode,
 		statTicker:        ticker.New(defaultStatInterval),
 		stats:             new(routerStats),