view mercurial/policy.py @ 29781:2654a0aac80d

profiling: move profiling code from dispatch.py (API)

Currently, profiling code lives in dispatch.py, which is a low-level
module centered around command dispatch. Furthermore, dispatch.py
imports a lot of other modules, meaning that importing dispatch.py
to get at profiling functionality would often result in a module import
cycle.

Profiling is a generic activity. It shouldn't be limited to command
dispatch. This patch moves profiling code from dispatch.py to the
new profiling.py. The low-level "run a profiler against a function"
functions have been moved verbatim. The code for determining how to
invoke the profiler has been extracted to its own function.

I decided to create a new module rather than stick this code
elsewhere (such as util.py) because util.py is already quite large.
And, I foresee this file growing larger once Facebook's profiling
enhancements get added to it.

# policy.py - module policy logic for Mercurial.
#
# Copyright 2015 Gregory Szorc <[e-mail]>
#
# 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
import sys

# Rules for how modules can be loaded. Values are:
#
#    c - require C extensions
#    allow - allow pure Python implementation when C loading fails
#    cffi - required cffi versions (implemented within pure module)
#    cffi-allow - allow pure Python implementation if cffi version is missing
#    py - only load pure Python modules
#
# By default, require the C extensions for performance reasons.
policy = 'c'
policynoc = ('cffi', 'cffi-allow', 'py')
policynocffi = ('c', 'py')

try:
    from . import __modulepolicy__
    policy = __modulepolicy__.modulepolicy
except ImportError:
    pass

# PyPy doesn't load C extensions.
#
# The canonical way to do this is to test platform.python_implementation().
# But we don't import platform and don't bloat for it here.
if '__pypy__' in sys.builtin_module_names:
    policy = 'cffi'

# Our C extensions aren't yet compatible with Python 3. So use pure Python
# on Python 3 for now.
if sys.version_info[0] >= 3:
    policy = 'py'

# Environment variable can always force settings.
policy = os.environ.get('HGMODULEPOLICY', policy)