view mercurial/txnutil.py @ 43778:888bd39ed555

lock: pass "success" boolean to _afterlock callbacks

This lets the callback decide if it should actually run or not. I suspect that
most callbacks (and hooks) *should not* run in this scenario, but I'm trying
to not break any existing behavior. `persistmanifestcache`, however, seems
actively dangerous to run: we just encountered an exception and the repo is in
an unknown state (hopefully a consistent one due to transactions, but this is
not 100% guaranteed), and the data we cache may be based on this unknown
state.

This was observed by our users since we wrap some of the functions that
persistmanifestcache calls and it expects that the repo object is in a certain
state that we'd set up earlier. If the user hits ctrl-c before we establish
that state, we end up crashing there. I'm going to  make that extension
resilient to this issue, but figured it might be a common issue and should be
handled here as well instead of just working around the issue.

Differential Revision: https://phab.mercurial-scm.org/D7459

# txnutil.py - transaction related utilities
#
#  Copyright FUJIWARA Katsunori <[e-mail]> and others
#
# 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 errno

from . import encoding


def mayhavepending(root):
    '''return whether 'root' may have pending changes, which are
    visible to this process.
    '''
    return root == encoding.environ.get(b'HG_PENDING')


def trypending(root, vfs, filename, **kwargs):
    '''Open  file to be read according to HG_PENDING environment variable

    This opens '.pending' of specified 'filename' only when HG_PENDING
    is equal to 'root'.

    This returns '(fp, is_pending_opened)' tuple.
    '''
    if mayhavepending(root):
        try:
            return (vfs(b'%s.pending' % filename, **kwargs), True)
        except IOError as inst:
            if inst.errno != errno.ENOENT:
                raise
    return (vfs(filename, **kwargs), False)