changeset 27193:c7217f1458bf

commands: make backout acquire locks before processing

Before this patch, "hg backout" executes below before acquisition of
wlock.

  - cmdutil.checkunfinished()
  - cmdutil.bailifchanged()
  - repo.dirstate.parents()

It may cause unintentional result, if another command runs parallelly
(see also issue4368).

In addition to it, "hg backout" refers changelog for purposes below
without acquisition of store lock (slock), and it may cause
unintentional result, if store is updated parallelly.

  - show and update to the revision by 'repo.changelog.tip()'

  - examine for "created new head" by 'repo.branchheads()' and
    'cmdutil.commitstatus()'

To avoid this issue, this patch makes "hg backout" acquire wlock and
slock before processing.

--- a/mercurial/commands.py	Wed Dec 02 03:12:07 2015 +0900
+++ b/mercurial/commands.py	Wed Dec 02 03:12:07 2015 +0900
@@ -574,6 +574,15 @@
     Returns 0 on success, 1 if nothing to backout or there are unresolved
     files.
     '''
+    wlock = lock = None
+    try:
+        wlock = repo.wlock()
+        lock = repo.lock()
+        return _dobackout(ui, repo, node, rev, commit, **opts)
+    finally:
+        release(lock, wlock)
+
+def _dobackout(ui, repo, node=None, rev=None, commit=False, **opts):
     if rev and node:
         raise error.Abort(_("please specify just one revision"))
 
@@ -612,7 +621,6 @@
         parent = p1
 
     # the backout should appear on the same branch
-    wlock = repo.wlock()
     try:
         branch = repo.dirstate.branch()
         bheads = repo.branchheads(branch)
@@ -675,7 +683,9 @@
             finally:
                 ui.setconfig('ui', 'forcemerge', '', '')
     finally:
-        wlock.release()
+        # TODO: get rid of this meaningless try/finally enclosing.
+        # this is kept only to reduce changes in a patch.
+        pass
     return 0
 
 @command('bisect',