revset: make filteredset.__nonzero__ respect the order of the filteredset
This fix allows __nonzero__ to respect the direction of iteration of the
whole filteredset. Here's the case when it matters. Imagine that we have a
very large repository and we want to execute a command like:
$ hg log --rev '(tip:0) and user(ikostia)' --limit 1
(we want to get the latest commit by me).
Mercurial will evaluate a filteredset lazy data structure, an
instance of the filteredset class, which will know that it has to iterate
in a descending order (isdescending() will return True if called). This
means that when some code iterates over the instance of this filteredset,
the 'and user(ikostia)' condition will be first checked on the latest
revision, then on the second latest and so on, allowing Mercurial to
print matches as it founds them. However, cmdutil.getgraphlogrevs
contains the following code:
revs = _logrevs(repo, opts)
if not revs:
return revset.baseset(), None, None
The "not revs" expression is evaluated by calling filteredset.__nonzero__,
which in its current implementation will try to iterate the filteredset
in ascending order until it finds a revision that matches the 'and user(..'
condition. If the condition is only true on late revisions, a lot of
useless iterations will be done. These iterations could be avoided if
__nonzero__ followed the order of the filteredset, which in my opinion
is a sensible thing to do here.
The problem gets even worse when instead of 'user(ikostia)' some more
expensive check is performed, like grepping the commit diff.
I tested this fix on a very large repo where tip is my commit and my very
first commit comes fairly late in the revision history. Results of timing
of the above command on that very large repo.
-with my fix:
real 0m1.795s
user 0m1.657s
sys 0m0.135s
-without my fix:
real 1m29.245s
user 1m28.223s
sys 0m0.929s
I understand that this is a very specific kind of problem that presents
itself very rarely, only on very big repositories and with expensive
checks and so on. But I don't see any disadvantages to this kind of fix
either.
# __init__.py - Startup and module loading logic for Mercurial.
#
# Copyright 2015 Gregory Szorc <gregory.szorc@gmail.com>
#
# 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 imp
import os
import sys
import zipimport
from . import (
policy
)
__all__ = []
modulepolicy = policy.policy
# Modules that have both Python and C implementations. See also the
# set of .py files under mercurial/pure/.
_dualmodules = set([
'mercurial.base85',
'mercurial.bdiff',
'mercurial.diffhelpers',
'mercurial.mpatch',
'mercurial.osutil',
'mercurial.parsers',
])
class hgimporter(object):
"""Object that conforms to import hook interface defined in PEP-302."""
def find_module(self, name, path=None):
# We only care about modules that have both C and pure implementations.
if name in _dualmodules:
return self
return None
def load_module(self, name):
mod = sys.modules.get(name, None)
if mod:
return mod
mercurial = sys.modules['mercurial']
# The zip importer behaves sufficiently differently from the default
# importer to warrant its own code path.
loader = getattr(mercurial, '__loader__', None)
if isinstance(loader, zipimport.zipimporter):
def ziploader(*paths):
"""Obtain a zipimporter for a directory under the main zip."""
path = os.path.join(loader.archive, *paths)
zl = sys.path_importer_cache.get(path)
if not zl:
zl = zipimport.zipimporter(path)
return zl
try:
if modulepolicy == 'py':
raise ImportError()
zl = ziploader('mercurial')
mod = zl.load_module(name)
# Unlike imp, ziploader doesn't expose module metadata that
# indicates the type of module. So just assume what we found
# is OK (even though it could be a pure Python module).
except ImportError:
if modulepolicy == 'c':
raise
zl = ziploader('mercurial', 'pure')
mod = zl.load_module(name)
sys.modules[name] = mod
return mod
# Unlike the default importer which searches special locations and
# sys.path, we only look in the directory where "mercurial" was
# imported from.
# imp.find_module doesn't support submodules (modules with ".").
# Instead you have to pass the parent package's __path__ attribute
# as the path argument.
stem = name.split('.')[-1]
try:
if modulepolicy == 'py':
raise ImportError()
modinfo = imp.find_module(stem, mercurial.__path__)
# The Mercurial installer used to copy files from
# mercurial/pure/*.py to mercurial/*.py. Therefore, it's possible
# for some installations to have .py files under mercurial/*.
# Loading Python modules when we expected C versions could result
# in a) poor performance b) loading a version from a previous
# Mercurial version, potentially leading to incompatibility. Either
# scenario is bad. So we verify that modules loaded from
# mercurial/* are C extensions. If the current policy allows the
# loading of .py modules, the module will be re-imported from
# mercurial/pure/* below.
if modinfo[2][2] != imp.C_EXTENSION:
raise ImportError('.py version of %s found where C '
'version should exist' % name)
except ImportError:
if modulepolicy == 'c':
raise
# Could not load the C extension and pure Python is allowed. So
# try to load them.
from . import pure
modinfo = imp.find_module(stem, pure.__path__)
if not modinfo:
raise ImportError('could not find mercurial module %s' %
name)
mod = imp.load_module(name, *modinfo)
sys.modules[name] = mod
return mod
# We automagically register our custom importer as a side-effect of loading.
# This is necessary to ensure that any entry points are able to import
# mercurial.* modules without having to perform this registration themselves.
if not any(isinstance(x, hgimporter) for x in sys.meta_path):
# meta_path is used before any implicit finders and before sys.path.
sys.meta_path.insert(0, hgimporter())