hgdemandimport/__init__.py

profile: upgrade the "profile" context manager to a full class

So far we have been able to use a simple decorator for this. However using the
current context manager makes the scope of the profiling in dispatch
constrainted and the time frame to decide to enable profiling quite limited
(using "maybeprofile")

This is the first step toward the ability to enable the profiling from within
the profiling scope. eg::

  with maybeprofiling(ui) as profiler:
      ...
      bar.foo():
      ...
      if options['profile']:
          profiler.start()
      ...
      fooz()
      ...

My target usecase is adding support for  "--profile" to alias definitions with
effect.  These are to be used with "profiling.output=blackbox" to gather data
about operation that get slow from time to time (eg: pull being minutes instead
of seconds from time to time).

Of course, in such case, the scope of the profiling would be smaller since
profiler would be started after running extensions 'reposetup' (and other
potentially costly logic), but these are not relevant for my target usecase
(multiple second commits, multiple tens of seconds pull).

Currently adding '--profile' to a command through alias requires to re-spin a
Mercurial binary (using "!$HG" in alias), which as a significant performance
impact, especially in context where startup performance is being worked on...

An alternative approach would be to stop using the context manager in dispatch
and move back to a try/finally setup.

# hgdemandimport - 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.

'''demandimport - automatic demand-loading of modules'''

# This is in a separate package from mercurial because in Python 3,
# demand loading is per-package. Keeping demandimport in the mercurial package
# would disable demand loading for any modules in mercurial.

from __future__ import absolute_import

import sys

if sys.version_info[0] >= 3:
    from . import demandimportpy3 as demandimport
else:
    from . import demandimportpy2 as demandimport

# Extensions can add to this list if necessary.
ignore = [
    '__future__',
    '_hashlib',
    # ImportError during pkg_resources/__init__.py:fixup_namespace_package
    '_imp',
    '_xmlplus',
    'fcntl',
    'nt', # pathlib2 tests the existence of built-in 'nt' module
    'win32com.gen_py',
    'win32com.shell', # 'appdirs' tries to import win32com.shell
    '_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
    '_sre', # issue4920
    'rfc822',
    'mimetools',
    'sqlalchemy.events', # has import-time side effects (issue5085)
    # setuptools 8 expects this module to explode early when not on windows
    'distutils.msvc9compiler',
    '__builtin__',
    'builtins',
    'urwid.command_map', # for pudb
    ]

_pypy = '__pypy__' in sys.builtin_module_names

if _pypy:
    ignore.extend([
        # _ctypes.pointer is shadowed by "from ... import pointer" (PyPy 5)
        '_ctypes.pointer',
    ])

demandimport.init(ignore)

# Re-export.
isenabled = demandimport.isenabled
enable = demandimport.enable
disable = demandimport.disable
deactivated = demandimport.deactivated