view CONTRIBUTORS @ 36701:d77c3b023393

lock: block signal interrupt while making a lock file

On Windows where symlink isn't supported, util.makelock() could leave an empty
file if interrupted immediately after os.open(). This empty lock never dies
as it has no process id recorded.

    ld = os.open(pathname, os.O_CREAT | os.O_WRONLY | os.O_EXCL)
    # an interrupt may occur here
    os.write(ld, info)
    os.close(ld)

This was a long-standing bug of TortoiseHg which runs a command-server and
kills it by CTRL_C_EVENT, reported by random Windows users.

https://bitbucket.org/tortoisehg/thg/issues/4873/#comment-43591129

At first, I tried to fix makelock() to clean up a stale lock file, which
turned out to be hard because any instructions may be interrupted by a
signal.

    ld = None
    try:
        # CALL_FUNCTION  # os.open(...)
        # an interrupt may occur here
        # STORE_FAST     # ld = ...
        ld = os.open(pathname, os.O_CREAT | os.O_WRONLY | os.O_EXCL)
        os.write(ld, info)
        ...
        return True
    except:
        if ld:
            ...
            os.unlink(pathname)
        return False

So I decided to block signals by temporarily replacing the signal handlers
so makelcok() and held = 1 will never be interrupted.

Many thanks to Fernando Najera for investigating the issue.

[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>