view CONTRIBUTORS @ 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.

[This file is here for historical purposes, all recent contributors
should appear in the changelog directly]

Andrea Arcangeli <andrea at suse.de>
Thomas Arendsen Hein <thomas at intevation.de>
Goffredo Baroncelli <kreijack at libero.it>
Muli Ben-Yehuda <mulix at mulix.org>
Mikael Berthe <mikael at lilotux.net>
Benoit Boissinot <bboissin at gmail.com>
Brendan Cully <brendan at kublai.com>
Vincent Danjean <vdanjean.ml at free.fr>
Jake Edge <jake at edge2.net>
Michael Fetterman <michael.fetterman at intel.com>
Edouard Gomez <ed.gomez at free.fr>
Eric Hopper <hopper at omnifarious.org>
Alecs King <alecsk at gmail.com>
Volker Kleinfeld <Volker.Kleinfeld at gmx.de>
Vadim Lebedev <vadim at mbdsys.com>
Christopher Li <hg at chrisli.org>
Chris Mason <mason at suse.com>
Colin McMillen <mcmillen at cs.cmu.edu>
Wojciech Milkowski <wmilkowski at interia.pl>
Chad Netzer <chad.netzer at gmail.com>
Bryan O'Sullivan <bos at serpentine.com>
Vicent Seguí Pascual <vseguip at gmail.com>
Sean Perry <shaleh at speakeasy.net>
Nguyen Anh Quynh <aquynh at gmail.com>
Ollivier Robert <roberto at keltia.freenix.fr>
Alexander Schremmer <alex at alexanderweb.de>
Arun Sharma <arun at sharma-home.net>
Josef "Jeff" Sipek <jeffpc at optonline.net>
Kevin Smith <yarcs at qualitycode.com>
TK Soh <teekaysoh at yahoo.com>
Radoslaw Szkodzinski <astralstorm at gorzow.mm.pl>
Samuel Tardieu <sam at rfc1149.net>
K Thananchayan <thananck at yahoo.com>
Andrew Thompson <andrewkt at aktzero.com>
Michael S. Tsirkin <mst at mellanox.co.il>
Rafael Villar Burke <pachi at mmn-arquitectos.com>
Tristan Wibberley <tristan at wibberley.org>
Mark Williamson <mark.williamson at cl.cam.ac.uk>