Mercurial > hg
view mercurial/demandimport.py @ 26375:3686fa2b8eee
windows: insert file positioning call between reads and writes
fopen() and fdopen() have a unique-to-Windows requirement that
transitions between read and write operations in files opened
in modes r+, w+, and a+ perform a file positioning call
(fsetpos, fseek, or rewind) in between. While the MSDN docs don't
say what will happen if this is not done, observations reveal
that Python raises an IOError with errno 0. Furthermore, I
/think/ this behavior isn't deterministic. But I can reproduce
it reliably with subsequent patches applied that open revlogs
in a+ mode and perform both reads and writes.
This patch introduces a proxy class for file handles opened
in r+, w+, and a+ mode on Windows. The class intercepts calls
and audits whether a file positioning function has been called
between read and write operations. If not, a dummy, no-op seek
to the current file position is performed. This appears to be
sufficient to "trick" Windows into allowing transitions between
read and writes without raising errors.
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Sun, 27 Sep 2015 18:46:53 -0700 |
parents | 3beed01daff9 |
children | f2bf76d3d567 |
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# demandimport.py - global demand-loading of modules for Mercurial # # Copyright 2006, 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. ''' demandimport - automatic demandloading of modules To enable this module, do: import demandimport; demandimport.enable() Imports of the following forms will be demand-loaded: import a, b.c import a.b as c from a import b,c # a will be loaded immediately These imports will not be delayed: from a import * b = __import__(a) ''' from __future__ import absolute_import import contextlib import os import sys # __builtin__ in Python 2, builtins in Python 3. try: import __builtin__ as builtins except ImportError: import builtins contextmanager = contextlib.contextmanager _origimport = __import__ nothing = object() # Python 3 doesn't have relative imports nor level -1. level = -1 if sys.version_info[0] >= 3: level = 0 _import = _origimport def _hgextimport(importfunc, name, globals, *args, **kwargs): try: return importfunc(name, globals, *args, **kwargs) except ImportError: if not globals: raise # extensions are loaded with "hgext_" prefix hgextname = 'hgext_%s' % name nameroot = hgextname.split('.', 1)[0] contextroot = globals.get('__name__', '').split('.', 1)[0] if nameroot != contextroot: raise # retry to import with "hgext_" prefix return importfunc(hgextname, globals, *args, **kwargs) class _demandmod(object): """module demand-loader and proxy""" def __init__(self, name, globals, locals, level=level): if '.' in name: head, rest = name.split('.', 1) after = [rest] else: head = name after = [] object.__setattr__(self, "_data", (head, globals, locals, after, level)) object.__setattr__(self, "_module", None) def _extend(self, name): """add to the list of submodules to load""" self._data[3].append(name) def _load(self): if not self._module: head, globals, locals, after, level = self._data mod = _hgextimport(_import, head, globals, locals, None, level) # load submodules def subload(mod, p): h, t = p, None if '.' in p: h, t = p.split('.', 1) if getattr(mod, h, nothing) is nothing: setattr(mod, h, _demandmod(p, mod.__dict__, mod.__dict__)) elif t: subload(getattr(mod, h), t) for x in after: subload(mod, x) # are we in the locals dictionary still? if locals and locals.get(head) == self: locals[head] = mod object.__setattr__(self, "_module", mod) def __repr__(self): if self._module: return "<proxied module '%s'>" % self._data[0] return "<unloaded module '%s'>" % self._data[0] def __call__(self, *args, **kwargs): raise TypeError("%s object is not callable" % repr(self)) def __getattribute__(self, attr): if attr in ('_data', '_extend', '_load', '_module'): return object.__getattribute__(self, attr) self._load() return getattr(self._module, attr) def __setattr__(self, attr, val): self._load() setattr(self._module, attr, val) def _demandimport(name, globals=None, locals=None, fromlist=None, level=level): if not locals or name in ignore or fromlist == ('*',): # these cases we can't really delay return _hgextimport(_import, name, globals, locals, fromlist, level) elif not fromlist: # import a [as b] if '.' in name: # a.b base, rest = name.split('.', 1) # email.__init__ loading email.mime if globals and globals.get('__name__', None) == base: return _import(name, globals, locals, fromlist, level) # if a is already demand-loaded, add b to its submodule list if base in locals: if isinstance(locals[base], _demandmod): locals[base]._extend(rest) return locals[base] return _demandmod(name, globals, locals, level) else: # There is a fromlist. # from a import b,c,d # from . import b,c,d # from .a import b,c,d # level == -1: relative and absolute attempted (Python 2 only). # level >= 0: absolute only (Python 2 w/ absolute_import and Python 3). # The modern Mercurial convention is to use absolute_import everywhere, # so modern Mercurial code will have level >= 0. if level >= 0: # Mercurial's enforced import style does not use # "from a import b,c,d" or "from .a import b,c,d" syntax. In # addition, this appears to be giving errors with some modules # for unknown reasons. Since we shouldn't be using this syntax # much, work around the problems. if name: return _hgextimport(_origimport, name, globals, locals, fromlist, level) mod = _hgextimport(_origimport, name, globals, locals, level=level) for x in fromlist: # Missing symbols mean they weren't defined in the module # itself which means they are sub-modules. if getattr(mod, x, nothing) is nothing: setattr(mod, x, _demandmod(x, mod.__dict__, locals, level=level)) return mod # But, we still need to support lazy loading of standard library and 3rd # party modules. So handle level == -1. mod = _hgextimport(_origimport, name, globals, locals) # recurse down the module chain for comp in name.split('.')[1:]: if getattr(mod, comp, nothing) is nothing: setattr(mod, comp, _demandmod(comp, mod.__dict__, mod.__dict__)) mod = getattr(mod, comp) for x in fromlist: # set requested submodules for demand load if getattr(mod, x, nothing) is nothing: setattr(mod, x, _demandmod(x, mod.__dict__, locals)) return mod ignore = [ '__future__', '_hashlib', '_xmlplus', 'fcntl', 'win32com.gen_py', '_winreg', # 2.7 mimetypes needs immediate ImportError 'pythoncom', # imported by tarfile, not available under Windows 'pwd', 'grp', # imported by profile, itself imported by hotshot.stats, # not available under Windows 'resource', # this trips up many extension authors 'gtk', # setuptools' pkg_resources.py expects "from __main__ import x" to # raise ImportError if x not defined '__main__', '_ssl', # conditional imports in the stdlib, issue1964 'rfc822', 'mimetools', # setuptools 8 expects this module to explode early when not on windows 'distutils.msvc9compiler' ] def isenabled(): return builtins.__import__ == _demandimport def enable(): "enable global demand-loading of modules" if os.environ.get('HGDEMANDIMPORT') != 'disable': builtins.__import__ = _demandimport def disable(): "disable global demand-loading of modules" builtins.__import__ = _origimport @contextmanager def deactivated(): "context manager for disabling demandimport in 'with' blocks" demandenabled = isenabled() if demandenabled: disable() try: yield finally: if demandenabled: enable()