comparison mercurial/context.py @ 25753:fe03f522dda9

context: write dirstate out explicitly after marking files as clean

To detect change of a file without redundant comparison of file
content, dirstate recognizes a file as certainly clean, if:

  (1) it is already known as "normal",
  (2) dirstate entry for it has valid (= not "-1") timestamp, and
  (3) mode, size and timestamp of it on the filesystem are as same as
      ones expected in dirstate

This works as expected in many cases, but doesn't in the corner case
that changing a file keeps mode, size and timestamp of it on the
filesystem.

The timetable below shows steps in one of typical such situations:

  ---- ----------------------------------- ----------------
                                           timestamp of "f"
                                           ----------------
                                           dirstate   file-
  time          action                     mem  file  system
  ---- ----------------------------------- ---- ----- -----
  N                                              -1    ***
       - make file "f" clean                            N

       - execute 'hg foobar'
         - instantiate 'dirstate'           -1   -1
         - 'dirstate.normal("f")'           N    -1
           (e.g. via dirty check)
         - change "f", but keep size                    N
  N+1
         - release wlock
           - 'dirstate.write()'             N    N

       - 'hg status' shows "f" as "clean"   N    N      N
  ---- ----------------------------------- ---- ----- -----

The most important point is that 'dirstate.write()' is executed at N+1
or later. This causes writing dirstate timestamp N of "f" out
successfully. If it is executed at N, 'parsers.pack_dirstate()'
replaces timestamp N with "-1" before actual writing dirstate out.

Occasional test failure for unexpected file status is typical example
of this corner case. Batch execution with small working directory is
finished in no time, and rarely satisfies condition (2) above.

This issue can occur in cases below;

  - 'hg revert --rev REV' for revisions other than the parent
  - failure of 'merge.update()' before 'merge.recordupdates()'

The root cause of this issue is that files are changed without
flushing in-memory dirstate changes via 'repo.commit()' (even though
omitting 'dirstate.normallookup()' on changed files also causes this
issue).

To detect changes of files correctly, this patch writes in-memory
dirstate changes out explicitly after marking files as clean in
'workingctx._checklookup()', which is invoked via 'repo.status()'.

After this change, timetable is changed as below:

  ---- ----------------------------------- ----------------
                                           timestamp of "f"
                                           ----------------
                                           dirstate   file-
  time          action                     mem  file  system
  ---- ----------------------------------- ---- ----- -----
  N                                              -1    ***
       - make file "f" clean                            N

       - execute 'hg foobar'
         - instantiate 'dirstate'           -1   -1
         - 'dirstate.normal("f")'           N    -1
           (e.g. via dirty check)
       ----------------------------------- ---- ----- -----
         - 'dirsttate.write()'              -1   -1
       ----------------------------------- ---- ----- -----
         - change "f", but keep size                    N
  N+1
         - release wlock
           - 'dirstate.write()'             -1   -1

       - 'hg status'                        -1   -1      N
  ---- ----------------------------------- ---- ----- -----

To reproduce this issue in tests certainly, this patch emulates some
timing critical actions as below:

  - timestamp of "f" in '.hg/dirstate' is -1 at the beginning

    'hg debugrebuildstate' before command invocation ensures it.

  - make file "f" clean at N
  - change "f" at N

    'touch -t 200001010000' before and after command invocation
    changes mtime of "f" to "2000-01-01 00:00" (= N).

  - invoke 'dirstate.write()' via 'repo.status()' at N

    'fakedirstatewritetime.py' forces 'pack_dirstate()' to use
    "2000-01-01 00:00" as "now", only if 'pack_dirstate()' is invoked
    via 'workingctx._checklookup()'.

  - invoke 'dirstate.write()' via releasing wlock at N+1 (or "not at N")

    'pack_dirstate()' via releasing wlock uses actual timestamp at
    runtime as "now", and it should be different from the "2000-01-01
    00:00" of "f".

BTW, this patch also changes 'test-largefiles-misc.t', because adding
'dirstate.write()' makes recent dirstate changes visible to external
process.

25752:815df73abf12

                wlock = self._repo.wlock(False)
                normal = self._repo.dirstate.normal
                try:
                    for f in fixup:
                        normal(f)
                finally:
                    wlock.release()
            except error.LockError:
                pass
        return modified, fixup

25753:fe03f522dda9

                wlock = self._repo.wlock(False)
                normal = self._repo.dirstate.normal
                try:
                    for f in fixup:
                        normal(f)
                    # write changes out explicitly, because nesting
                    # wlock at runtime may prevent 'wlock.release()'
                    # below from doing so for subsequent changing files
                    self._repo.dirstate.write()
                finally:
                    wlock.release()
            except error.LockError:
                pass
        return modified, fixup