Add local locks for spanner db driver

database/spanner/spanner.go

@@ -1,6 +1,7 @@
 package spanner
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -20,6 +21,7 @@ import (
 	"github.com/golang-migrate/migrate/v4/database"
 
 	"github.com/hashicorp/go-multierror"
+	uatomic "go.uber.org/atomic"
 	"google.golang.org/api/iterator"
 	adminpb "google.golang.org/genproto/googleapis/spanner/admin/database/v1"
 )
@@ -32,12 +34,19 @@ func init() {
 // DefaultMigrationsTable is used if no custom table is specified
 const DefaultMigrationsTable = "SchemaMigrations"
 
+const (
+	unlockedVal = 0
+	lockedVal   = 1
+)
+
 // Driver errors
 var (
-	ErrNilConfig      = fmt.Errorf("no config")
-	ErrNoDatabaseName = fmt.Errorf("no database name")
-	ErrNoSchema       = fmt.Errorf("no schema")
-	ErrDatabaseDirty  = fmt.Errorf("database is dirty")
+	ErrNilConfig      = errors.New("no config")
+	ErrNoDatabaseName = errors.New("no database name")
+	ErrNoSchema       = errors.New("no schema")
+	ErrDatabaseDirty  = errors.New("database is dirty")
+	ErrLockHeld       = errors.New("unable to obtain lock")
+	ErrLockNotHeld    = errors.New("unable to release already released lock")
 )
 
 // Config used for a Spanner instance
@@ -56,6 +65,8 @@ type Spanner struct {
 	db *DB
 
 	config *Config
+
+	lock *uatomic.Uint32
 }
 
 type DB struct {
@@ -87,6 +98,7 @@ func WithInstance(instance *DB, config *Config) (database.Driver, error) {
 	sx := &Spanner{
 		db:     instance,
 		config: config,
+		lock:   uatomic.NewUint32(unlockedVal),
 	}
 
 	if err := sx.ensureVersionTable(); err != nil {
@@ -143,12 +155,18 @@ func (s *Spanner) Close() error {
 // Lock implements database.Driver but doesn't do anything because Spanner only
 // enqueues the UpdateDatabaseDdlRequest.
 func (s *Spanner) Lock() error {
-	return nil
+	if swapped := s.lock.CAS(unlockedVal, lockedVal); swapped {
+		return nil
+	}
+	return ErrLockHeld
 }
 
 // Unlock implements database.Driver but no action required, see Lock.
 func (s *Spanner) Unlock() error {
-	return nil
+	if swapped := s.lock.CAS(lockedVal, unlockedVal); swapped {
+		return nil
+	}
+	return ErrLockNotHeld
 }
 
 // Run implements database.Driver

go.mod

@@ -44,6 +44,7 @@ require (
 	github.com/xdg/stringprep v1.0.0 // indirect
 	gitlab.com/nyarla/go-crypt v0.0.0-20160106005555-d9a5dc2b789b // indirect
 	go.mongodb.org/mongo-driver v1.1.0
+	go.uber.org/atomic v1.4.0
 	golang.org/x/crypto v0.0.0-20200709230013-948cd5f35899 // indirect
 	golang.org/x/net v0.0.0-20200813134508-3edf25e44fcc
 	golang.org/x/sys v0.0.0-20200817155316-9781c653f443 // indirect

go.sum

@@ -263,6 +263,7 @@ github.com/jmoiron/sqlx v1.2.0/go.mod h1:1FEQNm3xlJgrMD+FBdI9+xvCksHtbpVBBw5dYhB
 github.com/jstemmer/go-junit-report v0.0.0-20190106144839-af01ea7f8024/go.mod h1:6v2b51hI/fHJwM22ozAgKL4VKDeJcHhJFhtBdhmNjmU=
 github.com/jstemmer/go-junit-report v0.9.1 h1:6QPYqodiu3GuPL+7mfx+NwDdp2eTkp9IfEUpgAwUN0o=
 github.com/jstemmer/go-junit-report v0.9.1/go.mod h1:Brl9GWCQeLvo8nXZwPNNblvFj/XSXhF0NWZEnDohbsk=
+github.com/k0kubun/colorstring v0.0.0-20150214042306-9440f1994b88 h1:uC1QfSlInpQF+M0ao65imhwqKnz3Q2z/d8PWZRMQvDM=
 github.com/k0kubun/colorstring v0.0.0-20150214042306-9440f1994b88/go.mod h1:3w7q1U84EfirKl04SVQ/s7nPm1ZPhiXd34z40TNz36k=
 github.com/k0kubun/pp v2.3.0+incompatible h1:EKhKbi34VQDWJtq+zpsKSEhkHHs9w2P8Izbq8IhLVSo=
 github.com/k0kubun/pp v2.3.0+incompatible/go.mod h1:GWse8YhT0p8pT4ir3ZgBbfZild3tgzSScAn6HmfYukg=
@@ -381,6 +382,7 @@ go.opencensus.io v0.22.3/go.mod h1:yxeiOL68Rb0Xd1ddK5vPZ/oVn4vY4Ynel7k9FzqtOIw=
 go.opencensus.io v0.22.4 h1:LYy1Hy3MJdrCdMwwzxA/dRok4ejH+RwNGbuoD9fCjto=
 go.opencensus.io v0.22.4/go.mod h1:yxeiOL68Rb0Xd1ddK5vPZ/oVn4vY4Ynel7k9FzqtOIw=
 go.uber.org/atomic v1.3.2/go.mod h1:gD2HeocX3+yG+ygLZcrzQJaqmWj9AIm7n08wl/qW/PE=
+go.uber.org/atomic v1.4.0 h1:cxzIVoETapQEqDhQu3QfnvXAV4AlzcvUCxkVUFw3+EU=
 go.uber.org/atomic v1.4.0/go.mod h1:gD2HeocX3+yG+ygLZcrzQJaqmWj9AIm7n08wl/qW/PE=
 go.uber.org/multierr v1.1.0/go.mod h1:wR5kodmAFQ0UK8QlbwjlSNy0Z68gJhDJUG5sjR94q/0=
 go.uber.org/zap v1.9.1/go.mod h1:vwi/ZaCAaUcBkycHslxD9B2zi4UTXhF60s6SWpuDF0Q=