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 ± σ): 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 ± σ): 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 ± σ): 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 ± σ): 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 ± σ): 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 ± σ): 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
# filelog.py - file history class for mercurial
#
# Copyright 2005-2007 Matt Mackall <mpm@selenic.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
from .i18n import _
from .node import (
nullid,
nullrev,
)
from . import (
error,
revlog,
)
from .interfaces import (
repository,
util as interfaceutil,
)
from .utils import storageutil
@interfaceutil.implementer(repository.ifilestorage)
class filelog(object):
def __init__(self, opener, path):
self._revlog = revlog.revlog(
opener, b'/'.join((b'data', path + b'.i')), censorable=True
)
# Full name of the user visible file, relative to the repository root.
# Used by LFS.
self._revlog.filename = path
def __len__(self):
return len(self._revlog)
def __iter__(self):
return self._revlog.__iter__()
def hasnode(self, node):
if node in (nullid, nullrev):
return False
try:
self._revlog.rev(node)
return True
except (TypeError, ValueError, IndexError, error.LookupError):
return False
def revs(self, start=0, stop=None):
return self._revlog.revs(start=start, stop=stop)
def parents(self, node):
return self._revlog.parents(node)
def parentrevs(self, rev):
return self._revlog.parentrevs(rev)
def rev(self, node):
return self._revlog.rev(node)
def node(self, rev):
return self._revlog.node(rev)
def lookup(self, node):
return storageutil.fileidlookup(
self._revlog, node, self._revlog.indexfile
)
def linkrev(self, rev):
return self._revlog.linkrev(rev)
def commonancestorsheads(self, node1, node2):
return self._revlog.commonancestorsheads(node1, node2)
# Used by dagop.blockdescendants().
def descendants(self, revs):
return self._revlog.descendants(revs)
def heads(self, start=None, stop=None):
return self._revlog.heads(start, stop)
# Used by hgweb, children extension.
def children(self, node):
return self._revlog.children(node)
def iscensored(self, rev):
return self._revlog.iscensored(rev)
def revision(self, node, _df=None, raw=False):
return self._revlog.revision(node, _df=_df, raw=raw)
def rawdata(self, node, _df=None):
return self._revlog.rawdata(node, _df=_df)
def emitrevisions(
self,
nodes,
nodesorder=None,
revisiondata=False,
assumehaveparentrevisions=False,
deltamode=repository.CG_DELTAMODE_STD,
):
return self._revlog.emitrevisions(
nodes,
nodesorder=nodesorder,
revisiondata=revisiondata,
assumehaveparentrevisions=assumehaveparentrevisions,
deltamode=deltamode,
)
def addrevision(
self,
revisiondata,
transaction,
linkrev,
p1,
p2,
node=None,
flags=revlog.REVIDX_DEFAULT_FLAGS,
cachedelta=None,
):
return self._revlog.addrevision(
revisiondata,
transaction,
linkrev,
p1,
p2,
node=node,
flags=flags,
cachedelta=cachedelta,
)
def addgroup(
self,
deltas,
linkmapper,
transaction,
addrevisioncb=None,
maybemissingparents=False,
):
if maybemissingparents:
raise error.Abort(
_(
b'revlog storage does not support missing '
b'parents write mode'
)
)
return self._revlog.addgroup(
deltas, linkmapper, transaction, addrevisioncb=addrevisioncb
)
def getstrippoint(self, minlink):
return self._revlog.getstrippoint(minlink)
def strip(self, minlink, transaction):
return self._revlog.strip(minlink, transaction)
def censorrevision(self, tr, node, tombstone=b''):
return self._revlog.censorrevision(tr, node, tombstone=tombstone)
def files(self):
return self._revlog.files()
def read(self, node):
return storageutil.filtermetadata(self.revision(node))
def add(self, text, meta, transaction, link, p1=None, p2=None):
if meta or text.startswith(b'\1\n'):
text = storageutil.packmeta(meta, text)
return self.addrevision(text, transaction, link, p1, p2)
def renamed(self, node):
return storageutil.filerevisioncopied(self, node)
def size(self, rev):
"""return the size of a given revision"""
# for revisions with renames, we have to go the slow way
node = self.node(rev)
if self.renamed(node):
return len(self.read(node))
if self.iscensored(rev):
return 0
# XXX if self.read(node).startswith("\1\n"), this returns (size+4)
return self._revlog.size(rev)
def cmp(self, node, text):
"""compare text with a given file revision
returns True if text is different than what is stored.
"""
return not storageutil.filedataequivalent(self, node, text)
def verifyintegrity(self, state):
return self._revlog.verifyintegrity(state)
def storageinfo(
self,
exclusivefiles=False,
sharedfiles=False,
revisionscount=False,
trackedsize=False,
storedsize=False,
):
return self._revlog.storageinfo(
exclusivefiles=exclusivefiles,
sharedfiles=sharedfiles,
revisionscount=revisionscount,
trackedsize=trackedsize,
storedsize=storedsize,
)
# TODO these aren't part of the interface and aren't internal methods.
# Callers should be fixed to not use them.
# Used by bundlefilelog, unionfilelog.
@property
def indexfile(self):
return self._revlog.indexfile
@indexfile.setter
def indexfile(self, value):
self._revlog.indexfile = value
# Used by repo upgrade.
def clone(self, tr, destrevlog, **kwargs):
if not isinstance(destrevlog, filelog):
raise error.ProgrammingError(b'expected filelog to clone()')
return self._revlog.clone(tr, destrevlog._revlog, **kwargs)
class narrowfilelog(filelog):
"""Filelog variation to be used with narrow stores."""
def __init__(self, opener, path, narrowmatch):
super(narrowfilelog, self).__init__(opener, path)
self._narrowmatch = narrowmatch
def renamed(self, node):
res = super(narrowfilelog, self).renamed(node)
# Renames that come from outside the narrowspec are problematic
# because we may lack the base text for the rename. This can result
# in code attempting to walk the ancestry or compute a diff
# encountering a missing revision. We address this by silently
# removing rename metadata if the source file is outside the
# narrow spec.
#
# A better solution would be to see if the base revision is available,
# rather than assuming it isn't.
#
# An even better solution would be to teach all consumers of rename
# metadata that the base revision may not be available.
#
# TODO consider better ways of doing this.
if res and not self._narrowmatch(res[0]):
return None
return res
def size(self, rev):
# Because we have a custom renamed() that may lie, we need to call
# the base renamed() to report accurate results.
node = self.node(rev)
if super(narrowfilelog, self).renamed(node):
return len(self.read(node))
else:
return super(narrowfilelog, self).size(rev)
def cmp(self, node, text):
different = super(narrowfilelog, self).cmp(node, text)
# Because renamed() may lie, we may get false positives for
# different content. Check for this by comparing against the original
# renamed() implementation.
if different:
if super(narrowfilelog, self).renamed(node):
t2 = self.read(node)
return t2 != text
return different