Don't open a new file descriptor for a locked state.

state/local.go

@@ -119,8 +119,20 @@ func (s *LocalState) RefreshState() error {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 
+	if s.PathOut == "" {
+		s.PathOut = s.Path
+	}
+
 	var reader io.Reader
-	if !s.written {
+
+	// The s.Path file is only OK to read if we have not written any state out
+	// (in which case the same state needs to be read in), and no state output file
+	// has been opened (possibly via a lock) or the input path is different
+	// than the output path.
+	// This is important for Windows, as if the input file is the same as the
+	// output file, and the output file has been locked already, we can't open
+	// the file again.
+	if !s.written && (s.stateFileOut == nil || s.Path != s.PathOut) {
 		// we haven't written a state file yet, so load from Path
 		f, err := os.Open(s.Path)
 		if err != nil {

state/local_test.go

@@ -166,3 +166,42 @@ func testLocalState(t *testing.T) *LocalState {
 
 	return ls
 }
+
+// Make sure we can refresh while the state is locked
+func TestLocalState_refreshWhileLocked(t *testing.T) {
+	f, err := ioutil.TempFile("", "tf")
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	err = terraform.WriteState(TestStateInitial(), f)
+	f.Close()
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	s := &LocalState{Path: f.Name()}
+	defer os.Remove(s.Path)
+
+	// lock first
+	info := NewLockInfo()
+	info.Operation = "test"
+	lockID, err := s.Lock(info)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer func() {
+		if err := s.Unlock(lockID); err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	if err := s.RefreshState(); err != nil {
+		t.Fatal(err)
+	}
+
+	readState := s.State()
+	if readState == nil || readState.Lineage == "" {
+		t.Fatal("missing state")
+	}
+}

terraform/state.go

@@ -9,6 +9,7 @@ import (
 	"io"
 	"io/ioutil"
 	"log"
+	"os"
 	"reflect"
 	"sort"
 	"strconv"
@@ -1876,11 +1877,19 @@ var ErrNoState = errors.New("no state")
 // ReadState reads a state structure out of a reader in the format that
 // was written by WriteState.
 func ReadState(src io.Reader) (*State, error) {
+	// check for a nil file specifically, since that produces a platform
+	// specific error if we try to use it in a bufio.Reader.
+	if f, ok := src.(*os.File); ok && f == nil {
+		return nil, ErrNoState
+	}
+
 	buf := bufio.NewReader(src)
+
 	if _, err := buf.Peek(1); err != nil {
-		// the error is either io.EOF or "invalid argument", and both are from
-		// an empty state.
-		return nil, ErrNoState
+		if err == io.EOF {
+			return nil, ErrNoState
+		}
+		return nil, err
 	}
 
 	if err := testForV0State(buf); err != nil {