interp: add eval cancelation by semaphore

Makefile

@@ -18,5 +18,6 @@ generate: gen_all_syscall
 
 tests:
 	GO111MODULE=off go test -v ./...
+	GO111MODULE=off go test -race ./interp
 
 .PHONY: check gen_all_syscall gen_tests

cmd/yaegi/yaegi_test.go

@@ -0,0 +1,91 @@
+package main
+
+import (
+	"bytes"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func TestYaegiCmdCancel(t *testing.T) {
+	tmp, err := ioutil.TempDir("", "yaegi-")
+	if err != nil {
+		t.Fatalf("failed to create tmp directory: %v", err)
+	}
+	defer func() {
+		err = os.RemoveAll(tmp)
+		if err != nil {
+			t.Errorf("failed to clean up %v: %v", tmp, err)
+		}
+	}()
+
+	yaegi := filepath.Join(tmp, "yaegi")
+	build := exec.Command("go", "build", "-race", "-o", yaegi, ".")
+	err = build.Run()
+	if err != nil {
+		t.Fatalf("failed to build yaegi command: %v", err)
+	}
+
+	// Test src must be terminated by a single newline.
+	tests := []string{
+		"for {}\n",
+		"select {}\n",
+	}
+	for _, src := range tests {
+		cmd := exec.Command(yaegi)
+		in, err := cmd.StdinPipe()
+		if err != nil {
+			t.Errorf("failed to get stdin pipe to yaegi command: %v", err)
+		}
+		var outBuf, errBuf bytes.Buffer
+		cmd.Stdout = &outBuf
+		cmd.Stderr = &errBuf
+
+		// https://golang.org/doc/articles/race_detector.html#Options
+		cmd.Env = []string{`GORACE="halt_on_error=1"`}
+
+		err = cmd.Start()
+		if err != nil {
+			t.Fatalf("failed to start yaegi command: %v", err)
+		}
+
+		_, err = in.Write([]byte(src))
+		if err != nil {
+			t.Errorf("failed pipe test source to yaegi command: %v", err)
+		}
+		time.Sleep(100 * time.Millisecond)
+		err = cmd.Process.Signal(os.Interrupt)
+		if err != nil {
+			t.Errorf("failed to send os.Interrupt to yaegi command: %v", err)
+		}
+
+		_, err = in.Write([]byte("1+1\n"))
+		if err != nil {
+			t.Errorf("failed to probe race: %v", err)
+		}
+		err = in.Close()
+		if err != nil {
+			t.Errorf("failed to close stdin pipe: %v", err)
+		}
+
+		err = cmd.Wait()
+		if err != nil {
+			if cmd.ProcessState.ExitCode() == 66 { // See race_detector.html article.
+				t.Errorf("race detected running yaegi command canceling %q: %v", src, err)
+				if testing.Verbose() {
+					t.Log(&errBuf)
+				}
+			} else {
+				t.Errorf("error running yaegi command for %q: %v", src, err)
+			}
+			continue
+		}
+
+		if outBuf.String() != "context canceled\n2\n" {
+			t.Errorf("unexpected output: %q", &outBuf)
+		}
+	}
+}

interp/ast.go

@@ -8,6 +8,7 @@ import (
 	"go/token"
 	"reflect"
 	"strconv"
+	"sync/atomic"
 )
 
 // nkind defines the kind of AST, i.e. the grammar category
@@ -356,9 +357,9 @@ func (interp *Interpreter) ast(src, name string) (string, *node, error) {
 	var pkgName string
 
 	addChild := func(root **node, anc astNode, pos token.Pos, kind nkind, act action) *node {
-		interp.nindex++
 		var i interface{}
-		n := &node{anc: anc.node, interp: interp, index: interp.nindex, pos: pos, kind: kind, action: act, val: &i, gen: builtin[act]}
+		nindex := atomic.AddInt64(&interp.nindex, 1)
+		n := &node{anc: anc.node, interp: interp, index: nindex, pos: pos, kind: kind, action: act, val: &i, gen: builtin[act]}
 		n.start = n
 		if anc.node == nil {
 			*root = n
@@ -369,15 +370,15 @@ func (interp *Interpreter) ast(src, name string) (string, *node, error) {
 				if len(ancAst.List)+len(ancAst.Body) == len(anc.node.child) {
 					// All case clause children are collected.
 					// Split children in condition and body nodes to desambiguify the AST.
-					interp.nindex++
-					body := &node{anc: anc.node, interp: interp, index: interp.nindex, pos: pos, kind: caseBody, action: aNop, val: &i, gen: nop}
+					nindex = atomic.AddInt64(&interp.nindex, 1)
+					body := &node{anc: anc.node, interp: interp, index: nindex, pos: pos, kind: caseBody, action: aNop, val: &i, gen: nop}
 
 					if ts := anc.node.anc.anc; ts.kind == typeSwitch && ts.child[1].action == aAssign {
 						// In type switch clause, if a switch guard is assigned, duplicate the switch guard symbol
 						// in each clause body, so a different guard type can be set in each clause
 						name := ts.child[1].child[0].ident
-						interp.nindex++
-						gn := &node{anc: body, interp: interp, ident: name, index: interp.nindex, pos: pos, kind: identExpr, action: aNop, val: &i, gen: nop}
+						nindex = atomic.AddInt64(&interp.nindex, 1)
+						gn := &node{anc: body, interp: interp, ident: name, index: nindex, pos: pos, kind: identExpr, action: aNop, val: &i, gen: nop}
 						body.child = append(body.child, gn)
 					}
 
@@ -553,6 +554,9 @@ func (interp *Interpreter) ast(src, name string) (string, *node, error) {
 		case *ast.CommClause:
 			st.push(addChild(&root, anc, pos, commClause, aNop), nod)
 
+		case *ast.CommentGroup:
+			return false
+
 		case *ast.CompositeLit:
 			st.push(addChild(&root, anc, pos, compositeLitExpr, aCompositeLit), nod)
 
@@ -844,9 +848,9 @@ func (s *nodestack) top() astNode {
 
 // dup returns a duplicated node subtree
 func (interp *Interpreter) dup(nod, anc *node) *node {
-	interp.nindex++
+	nindex := atomic.AddInt64(&interp.nindex, 1)
 	n := *nod
-	n.index = interp.nindex
+	n.index = nindex
 	n.anc = anc
 	n.start = &n
 	n.pos = anc.pos