view mercurial/txnutil.py @ 36523:e7411fb7ba7f

wireprotoserver: ability to run an SSH server until an event is set

It seems useful to be able to start an SSH protocol server that
won't run forever and won't call sys.exit() when it stops. This
could be used to facilitate intra-process testing of the SSH
protocol, for example.

We teach the server function to loop until a threading.Event is set
and invent a new API to run the server until an event is set. It also
won't sys.exit() afterwards.

There aren't many callers of serve_forever(). So we could refactor
them relatively easily. But I was lazy.

threading.Event might be a bit heavyweight. An alternative would be
a list whose only elements is changed. We can't use a simple scalar
value like a bool or int because those types are immutable. Events
are what you use in systems programming for this use case, so the
use of threading.Event seems justified.

Differential Revision: https://phab.mercurial-scm.org/D2461

# 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)