view mercurial/txnutil.py @ 47349:7138c863d0a1

dirstate-v2: Skip readdir in status based on directory mtime

When calling `read_dir` during `status` and the directory is found to be
eligible for caching (see code comments), write the directory’s mtime to the
dirstate. The presence of a directory mtime in the dirstate is meaningful
and indicates eligibility.

When an eligible directory mtime is found in the dirstate and `stat()` shows
that the mtime has not changed, `status` can skip calling `read_dir` again
and instead rely on the names of child nodes in the dirstate tree.

The `tempfile` crate is used to create a temporary file in order to use its
modification time as "current time" with the same truncation as other files
and directories would have in their own modification time.

Differential Revision: https://phab.mercurial-scm.org/D10826

# 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)