hgdemandimport: apply lazy module loading to sys.meta_path finders
Python's `sys.meta_path` finders are the primary objects whose job it
is to find a module at import time. When `import` is called, Python
iterates objects in this list and calls `o.find_spec(...)` to find
a `ModuleSpec` (or None if the module couldn't be found by that
finder). If no meta path finder can find a module, import fails.
One of the default meta path finders is `PathFinder`. Its job is to
import modules from the filesystem and is probably the most important
importer. This finder looks at `sys.path` and `sys.path_hooks` to do
its job.
The `ModuleSpec` returned by `MetaPathImporter.find_spec()` has a
`loader` attribute, which defines the concrete module loader to use.
`sys.path_hooks` is a hook point for teaching `PathFinder` to
instantiate custom loader types.
Previously, we injected a custom `sys.path_hook` that told `PathFinder`
to wrap the default loaders with a loader that creates a module object
that is lazy.
This approach worked. But its main limitation was that it only applied
to the `PathFinder` meta path importer. There are other meta path
importers that are registered. And in the case of PyOxidizer loading
modules from memory, `PathFinder` doesn't come into play since
PyOxidizer's own meta path importer was handling all imports.
This commit changes our approach to lazy module loading by proxying
all meta path importers. Specifically, we overload the `find_spec()`
method to swap in a wrapped loader on the `ModuleSpec` before it
is returned. The end result of this is all meta path importers should
be lazy.
As much as I would have loved to utilize .__class__ manipulation to
achieve this, some meta path importers are implemented in C/Rust
in such a way that they cannot be monkeypatched. This is why we
use __getattribute__ to define a proxy.
Also, this change could theoretically open us up to regressions in
meta path importers whose loader is creating module objects which
can't be monkeypatched. But I'm not aware of any of these in the
wild. So I think we'll be safe.
According to hyperfine, this change yields a decent startup time win of
5-6ms:
```
Benchmark #1: ~/.pyenv/versions/3.6.10/bin/python ./hg version
Time (mean ? ?): 86.8 ms ? 0.5 ms [User: 78.0 ms, System: 8.7 ms]
Range (min ? max): 86.0 ms ? 89.1 ms 50 runs
Time (mean ? ?): 81.1 ms ? 2.7 ms [User: 74.5 ms, System: 6.5 ms]
Range (min ? max): 77.8 ms ? 90.5 ms 50 runs
Benchmark #2: ~/.pyenv/versions/3.7.6/bin/python ./hg version
Time (mean ? ?): 78.9 ms ? 0.6 ms [User: 70.2 ms, System: 8.7 ms]
Range (min ? max): 78.1 ms ? 81.2 ms 50 runs
Time (mean ? ?): 73.4 ms ? 0.6 ms [User: 65.3 ms, System: 8.0 ms]
Range (min ? max): 72.4 ms ? 75.7 ms 50 runs
Benchmark #3: ~/.pyenv/versions/3.8.1/bin/python ./hg version
Time (mean ? ?): 78.1 ms ? 0.6 ms [User: 70.2 ms, System: 7.9 ms]
Range (min ? max): 77.4 ms ? 80.9 ms 50 runs
Time (mean ? ?): 72.1 ms ? 0.4 ms [User: 64.4 ms, System: 7.6 ms]
Range (min ? max): 71.4 ms ? 74.1 ms 50 runs
```
Differential Revision: https://phab.mercurial-scm.org/D7954
# httpconnection.py - urllib2 handler for new http support
#
# Copyright 2005, 2006, 2007, 2008 Matt Mackall <mpm@selenic.com>
# Copyright 2006, 2007 Alexis S. L. Carvalho <alexis@cecm.usp.br>
# Copyright 2006 Vadim Gelfer <vadim.gelfer@gmail.com>
# Copyright 2011 Google, Inc.
#
# 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 os
from .i18n import _
from .pycompat import open
from . import (
pycompat,
util,
)
urlerr = util.urlerr
urlreq = util.urlreq
# moved here from url.py to avoid a cycle
class httpsendfile(object):
"""This is a wrapper around the objects returned by python's "open".
Its purpose is to send file-like objects via HTTP.
It do however not define a __len__ attribute because the length
might be more than Py_ssize_t can handle.
"""
def __init__(self, ui, *args, **kwargs):
self.ui = ui
self._data = open(*args, **kwargs)
self.seek = self._data.seek
self.close = self._data.close
self.write = self._data.write
self.length = os.fstat(self._data.fileno()).st_size
self._pos = 0
# We pass double the max for total because we currently have
# to send the bundle twice in the case of a server that
# requires authentication. Since we can't know until we try
# once whether authentication will be required, just lie to
# the user and maybe the push succeeds suddenly at 50%.
self._progress = ui.makeprogress(
_(b'sending'), unit=_(b'kb'), total=(self.length // 1024 * 2)
)
def read(self, *args, **kwargs):
ret = self._data.read(*args, **kwargs)
if not ret:
self._progress.complete()
return ret
self._pos += len(ret)
self._progress.update(self._pos // 1024)
return ret
def __enter__(self):
return self
def __exit__(self, exc_type, exc_val, exc_tb):
self.close()
# moved here from url.py to avoid a cycle
def readauthforuri(ui, uri, user):
uri = pycompat.bytesurl(uri)
# Read configuration
groups = {}
for key, val in ui.configitems(b'auth'):
if key in (b'cookiefile',):
continue
if b'.' not in key:
ui.warn(_(b"ignoring invalid [auth] key '%s'\n") % key)
continue
group, setting = key.rsplit(b'.', 1)
gdict = groups.setdefault(group, {})
if setting in (b'username', b'cert', b'key'):
val = util.expandpath(val)
gdict[setting] = val
# Find the best match
scheme, hostpath = uri.split(b'://', 1)
bestuser = None
bestlen = 0
bestauth = None
for group, auth in pycompat.iteritems(groups):
if user and user != auth.get(b'username', user):
# If a username was set in the URI, the entry username
# must either match it or be unset
continue
prefix = auth.get(b'prefix')
if not prefix:
continue
prefixurl = util.url(prefix)
if prefixurl.user and prefixurl.user != user:
# If a username was set in the prefix, it must match the username in
# the URI.
continue
# The URI passed in has been stripped of credentials, so erase the user
# here to allow simpler matching.
prefixurl.user = None
prefix = bytes(prefixurl)
p = prefix.split(b'://', 1)
if len(p) > 1:
schemes, prefix = [p[0]], p[1]
else:
schemes = (auth.get(b'schemes') or b'https').split()
if (
(prefix == b'*' or hostpath.startswith(prefix))
and (
len(prefix) > bestlen
or (
len(prefix) == bestlen
and not bestuser
and b'username' in auth
)
)
and scheme in schemes
):
bestlen = len(prefix)
bestauth = group, auth
bestuser = auth.get(b'username')
if user and not bestuser:
auth[b'username'] = user
return bestauth