blob: 0131b30228d5322034eaafde21bf3fccbdb85707 [file] [log] [blame]
// Copyright 2017 The LUCI Authors.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
// +build darwin linux freebsd netbsd openbsd android
package vpython
import (
// systemSpecificLaunch launches the process described by "cmd" while ensuring
// that the VirtualEnv lock is held throughout its duration (best effort).
// On Linux/Mac, we use "execve" to *become* the target process. We need to
// continue to hold the lock for that process, though. We do this by passing it
// as an open file handle to the subprocess.
// This can be error-prone, as it places the burden on the subprocess to
// manage the file descriptor.
func systemSpecificLaunch(c context.Context, ve *venv.Env, cl *python.CommandLine, env environ.Env, dir string) error {
return Exec(c, ve.Interpreter(), cl, env, dir, func() error {
// Clear the close-on-exec flag, which Go enables by default.
lockFD := ve.LockHandle.LockFile().Fd()
fdFlags, err := unix.FcntlInt(lockFD, unix.F_GETFD, 0)
if err != nil {
return errors.Annotate(err, "could not get flags for lock file").Err()
if _, err := unix.FcntlInt(lockFD, unix.F_SETFD,
fdFlags & ^unix.FD_CLOEXEC); err != nil {
return errors.Annotate(err, "could not remove close-on-exec for lock file").Err()
return nil
func execImpl(c context.Context, argv []string, env environ.Env, dir string, setupFn func() error) error {
// Change directory.
if dir != "" {
if err := os.Chdir(dir); err != nil {
return errors.Annotate(err, "failed to chdir to %q", dir).Err()
// At this point, ANY ERROR will be fatal (panic). We assume that each
// operation may permanently alter our runtime environment.
if setupFn != nil {
if err := setupFn(); err != nil {
if err := syscall.Exec(argv[0], argv, env.Sorted()); err != nil {
panic(errors.Annotate(err, "failed to execve %q", argv[0]).Err())
panic("must not return")