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view hgdemandimport/demandimportpy3.py @ 44417:8f7c6656ac79
rust-nodemap: pure Rust example
To run, use `cargo run --release --example nodemap`
This demonstrates that simple scenarios entirely written
in Rust can content themselves with `NodeTree<T>`.
The example mmaps both the nodemap file and the changelog index.
We had of course to include an implementation of `RevlogIndex`
directly, which isn't much at this stage. It felt a bit
prematurate to include it in the lib.
Here are some first performance measurements, obtained with
this example, on a clone of mozilla-central with 440000
changesets:
(create) Nodemap constructed in RAM in 153.638305ms
(query CAE63161B68962) found in 22.362us: Ok(Some(269489))
(bench) Did 3 queries in 36.418µs (mean 12.139µs)
(bench) Did 50 queries in 184.318µs (mean 3.686µs)
(bench) Did 100000 queries in 31.053461ms (mean 310ns)
To be fair, even between bench runs, results tend to depend whether
the file is still in kernel caches, and it's not so easy to
get back to a real cold start. The worst we've seen was in the
50us ballpark.
In any busy server setting, the pages would always be in RAM.
We hope it's good enough not to be significantly slower on any
concrete Mercurial operation than the C nodetree when fully in RAM,
and of course this implementation has the serious headstart advantage
of persistence.
Differential Revision: https://phab.mercurial-scm.org/D7797
author | Georges Racinet <georges.racinet@octobus.net> |
---|---|
date | Tue, 18 Feb 2020 19:11:15 +0100 |
parents | f81c17ec303c |
children | a6e12d477595 |
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# demandimportpy3 - global demand-loading of modules for Mercurial # # Copyright 2017 Facebook Inc. # # This software may be used and distributed according to the terms of the # GNU General Public License version 2 or any later version. """Lazy loading for Python 3.6 and above. This uses the new importlib finder/loader functionality available in Python 3.5 and up. The code reuses most of the mechanics implemented inside importlib.util, but with a few additions: * Allow excluding certain modules from lazy imports. * Expose an interface that's substantially the same as demandimport for Python 2. This also has some limitations compared to the Python 2 implementation: * Much of the logic is per-package, not per-module, so any packages loaded before demandimport is enabled will not be lazily imported in the future. In practice, we only expect builtins to be loaded before demandimport is enabled. """ # This line is unnecessary, but it satisfies test-check-py3-compat.t. from __future__ import absolute_import import contextlib import importlib.util import sys from . import tracing _deactivated = False # Python 3.5's LazyLoader doesn't work for some reason. # https://bugs.python.org/issue26186 is a known issue with extension # importing. But it appears to not have a meaningful effect with # Mercurial. _supported = sys.version_info[0:2] >= (3, 6) class _lazyloaderex(importlib.util.LazyLoader): """This is a LazyLoader except it also follows the _deactivated global and the ignore list. """ def exec_module(self, module): """Make the module load lazily.""" with tracing.log('demandimport %s', module): if _deactivated or module.__name__ in ignores: self.loader.exec_module(module) else: super().exec_module(module) class LazyFinder(object): """A wrapper around a ``MetaPathFinder`` that makes loaders lazy. ``sys.meta_path`` finders have their ``find_spec()`` called to locate a module. This returns a ``ModuleSpec`` if found or ``None``. The ``ModuleSpec`` has a ``loader`` attribute, which is called to actually load a module. Our class wraps an existing finder and overloads its ``find_spec()`` to replace the ``loader`` with our lazy loader proxy. We have to use __getattribute__ to proxy the instance because some meta path finders don't support monkeypatching. """ __slots__ = ("_finder",) def __init__(self, finder): object.__setattr__(self, "_finder", finder) def __repr__(self): return "<LazyFinder for %r>" % object.__getattribute__(self, "_finder") # __bool__ is canonical Python 3. But check-code insists on __nonzero__ being # defined via `def`. def __nonzero__(self): return bool(object.__getattribute__(self, "_finder")) __bool__ = __nonzero__ def __getattribute__(self, name): if name in ("_finder", "find_spec"): return object.__getattribute__(self, name) return getattr(object.__getattribute__(self, "_finder"), name) def __delattr__(self, name): return delattr(object.__getattribute__(self, "_finder")) def __setattr__(self, name, value): return setattr(object.__getattribute__(self, "_finder"), name, value) def find_spec(self, *args, **kwargs): finder = object.__getattribute__(self, "_finder") spec = finder.find_spec(*args, **kwargs) # Lazy loader requires exec_module(). if ( spec is not None and spec.loader is not None and getattr(spec.loader, "exec_module") ): spec.loader = _lazyloaderex(spec.loader) return spec ignores = set() def init(ignoreset): global ignores ignores = ignoreset def isenabled(): return not _deactivated and any( isinstance(finder, LazyFinder) for finder in sys.meta_path ) def disable(): new_finders = [] for finder in sys.meta_path: new_finders.append( finder._finder if isinstance(finder, LazyFinder) else finder ) sys.meta_path[:] = new_finders def enable(): if not _supported: return new_finders = [] for finder in sys.meta_path: new_finders.append( LazyFinder(finder) if not isinstance(finder, LazyFinder) else finder ) sys.meta_path[:] = new_finders @contextlib.contextmanager def deactivated(): # This implementation is a bit different from Python 2's. Python 3 # maintains a per-package finder cache in sys.path_importer_cache (see # PEP 302). This means that we can't just call disable + enable. # If we do that, in situations like: # # demandimport.enable() # ... # from foo.bar import mod1 # with demandimport.deactivated(): # from foo.bar import mod2 # # mod2 will be imported lazily. (The converse also holds -- whatever finder # first gets cached will be used.) # # Instead, have a global flag the LazyLoader can use. global _deactivated demandenabled = isenabled() if demandenabled: _deactivated = True try: yield finally: if demandenabled: _deactivated = False