view mercurial/txnutil.py @ 41221:73203cdfe3fe

revset: detect integer list on parsing

Right now, using "%ld" with `repo.revs("…%ld…", somerevs)` is very
inefficient, all items in `somerevs` will be serialized to ascii and then
reparsed as integers. If `somerevs` contains just an handful of entry this is
fine, however, when you get to thousands or hundreds of thousands of revisions
this becomes very slow.

To avoid this serialization we need to first detect this situation. The code
involved in the whole process is quite complex so we start simple and focus on
some "simple" but widespread cases.

So far we only detect the situation and don't do anything special about it.
The singled out will be serialized in `formatspec` in the same way as before.

# 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('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('%s.pending' % filename, **kwargs), True)
        except IOError as inst:
            if inst.errno != errno.ENOENT:
                raise
    return (vfs(filename, **kwargs), False)