hg

lock: avoid unintentional lock acquisition at failure of readlock

Acquiring lock by vfs.makelock() and getting lock holder (aka
"locker") information by vfs.readlock() aren't atomic action.
Therefore, failure of the former doesn't ensure success of the latter.

Before this patch, lock is unintentionally acquired, if ENOENT
causes failure of vfs.readlock() while 5 times retrying, because
lock._trylock() returns to caller silently after retrying, and
lock.lock() assumes that lock._trylock() returns successfully only if
lock is acquired.

In this case, lock symlink (or file) isn't created, even though lock
is treated as acquired in memory.

To avoid this issue, this patch makes lock._trylock() raise
LockHeld(EAGAIN) at the end of it, if lock isn't acquired while
retrying.

An empty "locker" meaning "busy for frequent lock/unlock by many
processes" might appear in an abortion message, if lock acquisition
fails. Therefore, this patch also does:

  - use '%r' to increase visibility of "locker", even if it is empty
  - show hint message to explain what empty "locker" means

#!/usr/bin/env python
#
# mercurial - scalable distributed SCM
#
# Copyright 2005-2007 Matt Mackall <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

import os
import sys

if os.environ.get('HGUNICODEPEDANTRY', False):
    try:
        reload(sys)
        sys.setdefaultencoding("undefined")
    except NameError:
        pass

libdir = '@LIBDIR@'

if libdir != '@' 'LIBDIR' '@':
    if not os.path.isabs(libdir):
        libdir = os.path.join(os.path.dirname(os.path.realpath(__file__)),
                              libdir)
        libdir = os.path.abspath(libdir)
    sys.path.insert(0, libdir)

# enable importing on demand to reduce startup time
try:
    if sys.version_info[0] < 3:
        from mercurial import demandimport; demandimport.enable()
except ImportError:
    sys.stderr.write("abort: couldn't find mercurial libraries in [%s]\n" %
                     ' '.join(sys.path))
    sys.stderr.write("(check your install and PYTHONPATH)\n")
    sys.exit(-1)

import mercurial.util
import mercurial.dispatch

for fp in (sys.stdin, sys.stdout, sys.stderr):
    mercurial.util.setbinary(fp)

mercurial.dispatch.run()