annotate hgext/remotefilelog/extutil.py @ 41720:6704696141b8

templates: adding a config() function for template customization

This allows templates to be written such that users can customize them easily,
or that they can be customized based on other configuration of the system.  For
enterprise deployments, we often have complex template aliases, and right now
the only way individual users can customize those is by replacing the whole
template alias (which means they won't get company-wide updates to it anymore,
plus most users don't want to have to get a complex template right).
With this change, they can just set a config option which feeds into our
templates for common changes (e.g. whether to limit commit descriptions to the
width of their terminal or not).

To work around the issue of having to register the config options, I declared
a dedicated section [templateconfig] for these options to be dynamically
declared. They can still reference any other config option that's registered
elsewhere.

I only did string, bool and int at this time - list and date would add other
complications with parsing the default so I'll leave that as an exercise to
the reader :)

Differential Revision: https://phab.mercurial-scm.org/D5959

# extutil.py - useful utility methods for extensions
#
# Copyright 2016 Facebook
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

import contextlib
import errno
import os
import time

from mercurial import (
    error,
    lock as lockmod,
    util,
    vfs as vfsmod,
)

@contextlib.contextmanager
def flock(lockpath, description, timeout=-1):
    """A flock based lock object. Currently it is always non-blocking.

    Note that since it is flock based, you can accidentally take it multiple
    times within one process and the first one to be released will release all
    of them. So the caller needs to be careful to not create more than one
    instance per lock.
    """

    # best effort lightweight lock
    try:
        import fcntl
        fcntl.flock
    except ImportError:
        # fallback to Mercurial lock
        vfs = vfsmod.vfs(os.path.dirname(lockpath))
        with lockmod.lock(vfs, os.path.basename(lockpath), timeout=timeout):
            yield
        return
    # make sure lock file exists
    util.makedirs(os.path.dirname(lockpath))
    with open(lockpath, 'a'):
        pass
    lockfd = os.open(lockpath, os.O_RDONLY, 0o664)
    start = time.time()
    while True:
        try:
            fcntl.flock(lockfd, fcntl.LOCK_EX | fcntl.LOCK_NB)
            break
        except IOError as ex:
            if ex.errno == errno.EAGAIN:
                if timeout != -1 and time.time() - start > timeout:
                    raise error.LockHeld(errno.EAGAIN, lockpath, description,
                                         '')
                else:
                    time.sleep(0.05)
                    continue
            raise

    try:
        yield
    finally:
        fcntl.flock(lockfd, fcntl.LOCK_UN)
        os.close(lockfd)