tests/test-check-interfaces.py

lock: block signal interrupt while making a lock file

On Windows where symlink isn't supported, util.makelock() could leave an empty
file if interrupted immediately after os.open(). This empty lock never dies
as it has no process id recorded.

    ld = os.open(pathname, os.O_CREAT | os.O_WRONLY | os.O_EXCL)
    # an interrupt may occur here
    os.write(ld, info)
    os.close(ld)

This was a long-standing bug of TortoiseHg which runs a command-server and
kills it by CTRL_C_EVENT, reported by random Windows users.

https://bitbucket.org/tortoisehg/thg/issues/4873/#comment-43591129

At first, I tried to fix makelock() to clean up a stale lock file, which
turned out to be hard because any instructions may be interrupted by a
signal.

    ld = None
    try:
        # CALL_FUNCTION  # os.open(...)
        # an interrupt may occur here
        # STORE_FAST     # ld = ...
        ld = os.open(pathname, os.O_CREAT | os.O_WRONLY | os.O_EXCL)
        os.write(ld, info)
        ...
        return True
    except:
        if ld:
            ...
            os.unlink(pathname)
        return False

So I decided to block signals by temporarily replacing the signal handlers
so makelcok() and held = 1 will never be interrupted.

Many thanks to Fernando Najera for investigating the issue.

# Test that certain objects conform to well-defined interfaces.

from __future__ import absolute_import, print_function

from mercurial import (
    bundlerepo,
    httppeer,
    localrepo,
    sshpeer,
    statichttprepo,
    ui as uimod,
    unionrepo,
)

def checkobject(o):
    """Verify a constructed object conforms to interface rules.

    An object must have __abstractmethods__ defined.

    All "public" attributes of the object (attributes not prefixed with
    an underscore) must be in __abstractmethods__ or appear on a base class
    with __abstractmethods__.
    """
    name = o.__class__.__name__

    allowed = set()
    for cls in o.__class__.__mro__:
        if not getattr(cls, '__abstractmethods__', set()):
            continue

        allowed |= cls.__abstractmethods__
        allowed |= {a for a in dir(cls) if not a.startswith('_')}

    if not allowed:
        print('%s does not have abstract methods' % name)
        return

    public = {a for a in dir(o) if not a.startswith('_')}

    for attr in sorted(public - allowed):
        print('public attributes not in abstract interface: %s.%s' % (
            name, attr))

# Facilitates testing localpeer.
class dummyrepo(object):
    def __init__(self):
        self.ui = uimod.ui()
    def filtered(self, name):
        pass
    def _restrictcapabilities(self, caps):
        pass

# Facilitates testing sshpeer without requiring an SSH server.
class badpeer(httppeer.httppeer):
    def __init__(self):
        super(badpeer, self).__init__(uimod.ui(), 'http://localhost')
        self.badattribute = True

    def badmethod(self):
        pass

class dummypipe(object):
    def close(self):
        pass

def main():
    ui = uimod.ui()

    checkobject(badpeer())
    checkobject(httppeer.httppeer(ui, 'http://localhost'))
    checkobject(localrepo.localpeer(dummyrepo()))
    checkobject(sshpeer.sshv1peer(ui, 'ssh://localhost/foo', None, dummypipe(),
                                  dummypipe(), None, None))
    checkobject(sshpeer.sshv2peer(ui, 'ssh://localhost/foo', None, dummypipe(),
                                  dummypipe(), None, None))
    checkobject(bundlerepo.bundlepeer(dummyrepo()))
    checkobject(statichttprepo.statichttppeer(dummyrepo()))
    checkobject(unionrepo.unionpeer(dummyrepo()))

main()