Refactor ntfnstate mutex. (#85)

This refactors the notification state mutex out of the state itself to
the client.  This is being done since the code makes a copy of the
notification state and accesses that copy immutably, and therefore there
is no need for it to have its own mutex.

infrastructure.go

@@ -145,8 +145,9 @@ type Client struct {
 	requestList *list.List
 
 	// Notifications.
-	ntfnHandlers *NotificationHandlers
+	ntfnHandlers  *NotificationHandlers
-	ntfnState    *notificationState
+	ntfnStateLock sync.Mutex
+	ntfnState     *notificationState
 
 	// Networking infrastructure.
 	sendChan        chan []byte
@@ -233,8 +234,8 @@ func (c *Client) trackRegisteredNtfns(cmd interface{}) {
 		return
 	}
 
-	c.ntfnState.Lock()
+	c.ntfnStateLock.Lock()
-	defer c.ntfnState.Unlock()
+	defer c.ntfnStateLock.Unlock()
 
 	switch bcmd := cmd.(type) {
 	case *btcjson.NotifyBlocksCmd:
@@ -498,7 +499,9 @@ func (c *Client) reregisterNtfns() error {
 	// the notification state (while not under the lock of course) which
 	// also register it with the remote RPC server, so this prevents double
 	// registrations.
+	c.ntfnStateLock.Lock()
 	stateCopy := c.ntfnState.Copy()
+	c.ntfnStateLock.Unlock()
 
 	// Reregister notifyblocks if needed.
 	if stateCopy.notifyBlocks {

notify.go

@@ -10,7 +10,6 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"sync"
 	"time"
 
 	"github.com/btcsuite/btcd/btcjson"
@@ -32,7 +31,6 @@ var (
 // registered notification so the state can be automatically re-established on
 // reconnect.
 type notificationState struct {
-	sync.Mutex
 	notifyBlocks       bool
 	notifyNewTx        bool
 	notifyNewTxVerbose bool
@@ -41,12 +39,7 @@ type notificationState struct {
 }
 
 // Copy returns a deep copy of the receiver.
-//
-// This function is safe for concurrent access.
 func (s *notificationState) Copy() *notificationState {
-	s.Lock()
-	defer s.Unlock()
-
 	var stateCopy notificationState
 	stateCopy.notifyBlocks = s.notifyBlocks
 	stateCopy.notifyNewTx = s.notifyNewTx