Add detection for locked git repos.

gclient_scm.py

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Gclient-specific SCM-specific operations."""
 
 from __future__ import print_function
 
 import errno
 import logging
@@ skipping 1058 matching lines @@
   def _IsRebasing(self):
     # Check for any of REBASE-i/REBASE-m/REBASE/AM. Unfortunately git doesn't
     # have a plumbing command to determine whether a rebase is in progress, so
     # for now emualate (more-or-less) git-rebase.sh / git-completion.bash
     g = os.path.join(self.checkout_path, '.git')
     return (
       os.path.isdir(os.path.join(g, "rebase-merge")) or
       os.path.isdir(os.path.join(g, "rebase-apply")))
 
   def _CheckClean(self, rev_str):
+    lockfile = os.path.join(self.checkout_path, ".git", "index.lock")
+    if os.path.exists(lockfile):
+      raise gclient_utils.Error(
+        '\n____ %s%s\n'
+        '\tYour repo is locked, possibly due to a concurrent git process.\n'
+        '\tIf no git executable is running, then clean up %r and try again.\n'
+        % (self.relpath, rev_str, lockfile))
+
     # Make sure the tree is clean; see git-rebase.sh for reference
     try:
       scm.GIT.Capture(['update-index', '--ignore-submodules', '--refresh'],
                       cwd=self.checkout_path)
     except subprocess2.CalledProcessError:
       raise gclient_utils.Error('\n____ %s%s\n'
                                 '\tYou have unstaged changes.\n'
                                 '\tPlease commit, stash, or reset.\n'
                                   % (self.relpath, rev_str))
     try:
@@ skipping 592 matching lines @@
       new_command.append('--force')
       if command[0] != 'checkout' and scm.SVN.AssertVersion('1.6')[0]:
         new_command.extend(('--accept', 'theirs-conflict'))
     elif options.manually_grab_svn_rev:
       new_command.append('--force')
       if command[0] != 'checkout' and scm.SVN.AssertVersion('1.6')[0]:
         new_command.extend(('--accept', 'postpone'))
     elif command[0] != 'checkout' and scm.SVN.AssertVersion('1.6')[0]:
       new_command.extend(('--accept', 'postpone'))
     return new_command