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| author | iancottrell@chromium.org <iancottrell@chromium.org@0039d316-1c4b-4281-b951-d872f2087c98> | 2013-11-13 17:22:51 +0000 |
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| committer | iancottrell@chromium.org <iancottrell@chromium.org@0039d316-1c4b-4281-b951-d872f2087c98> | 2013-11-13 17:22:51 +0000 |
| commit | 61a85f474124c99fefe4fcc87e19dc26e549dd12 (patch) | |
| tree | d2d5574dbb1b9fc2f08507115b25adf3f82f975a | |
| parent | 840fe15f84e2ccfc98d87be673ff5c2d8e9f2691 (diff) | |
| download | chromium_src-61a85f474124c99fefe4fcc87e19dc26e549dd12.zip chromium_src-61a85f474124c99fefe4fcc87e19dc26e549dd12.tar.gz chromium_src-61a85f474124c99fefe4fcc87e19dc26e549dd12.tar.bz2 | |
Adding in the module scan and load system.
BUG=316397
Review URL: https://codereview.chromium.org/70083003
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234839 0039d316-1c4b-4281-b951-d872f2087c98
| -rw-r--r-- | tools/cr/cr/loader.py | 123 |
1 files changed, 123 insertions, 0 deletions
diff --git a/tools/cr/cr/loader.py b/tools/cr/cr/loader.py new file mode 100644 index 0000000..ecb251b --- /dev/null +++ b/tools/cr/cr/loader.py @@ -0,0 +1,123 @@ +# Copyright 2013 The Chromium Authors. All rights reserved. +# Use of this source code is governed by a BSD-style license that can be +# found in the LICENSE file. + +"""Module scan and load system. + +The main interface to this module is the Scan function, which triggers a +recursive scan of all packages and modules below cr, with modules being +imported as they are found. +This allows all the plugins in the system to self register. +The aim is to make writing plugins as simple as possible, minimizing the +boilerplate so the actual functionality is clearer. +""" +from importlib import import_module +import os +import sys + +import cr + +# This is the name of the variable inserted into modules to track which +# scanners have been applied. +_MODULE_SCANNED_TAG = '_CR_MODULE_SCANNED' + + +class AutoExport(object): + """A marker for classes that should be promoted up into the cr namespace.""" + + +def _AutoExportScanner(module): + """Scan the modules for things that need wiring up automatically.""" + for name, value in module.__dict__.items(): + if isinstance(value, type) and issubclass(value, AutoExport): + # Add this straight to the cr module. + if not hasattr(cr, name): + setattr(cr, name, value) + + +scan_hooks = [_AutoExportScanner] + + +def _Import(name): + """Import a module or package if it is not already imported.""" + module = sys.modules.get(name, None) + if module is not None: + return module + return import_module(name, None) + + +def _ScanModule(module): + """Runs all the scan_hooks for a module.""" + scanner_tags = getattr(module, _MODULE_SCANNED_TAG, None) + if scanner_tags is None: + # First scan, add the scanned marker set. + scanner_tags = set() + setattr(module, _MODULE_SCANNED_TAG, scanner_tags) + for scan in scan_hooks: + if scan not in scanner_tags: + scanner_tags.add(scan) + scan(module) + + +def _ScanPackage(package): + """Scan a package for child packages and modules.""" + modules = [] + # Recurse sub folders. + for path in package.__path__: + try: + basenames = os.listdir(path) + except OSError: + basenames = [] + for basename in basenames: + fullpath = os.path.join(path, basename) + if os.path.isdir(fullpath): + name = '.'.join([package.__name__, basename]) + child = _Import(name) + modules.extend(_ScanPackage(child)) + elif basename.endswith('.py') and not basename.startswith('_'): + name = '.'.join([package.__name__, basename[:-3]]) + modules.append(name) + return modules + + +def Scan(): + """Scans from the cr package down, loading modules as needed. + + This finds all packages and modules below the cr package, by scanning the + file system. It imports all the packages, and then runs post import hooks on + each module to do any automated work. One example of this is the hook that + finds all classes that extend AutoExport and copies them up into the cr + namespace directly. + + Modules are allowed to refer to each other, their import will be retried + until it succeeds or no progress can be made on any module. + """ + remains = _ScanPackage(cr) + progress = True + modules = [] + while progress and remains: + progress = False + todo = remains + remains = [] + for name in todo: + try: + module = _Import(name) + modules.append(module) + _ScanModule(module) + progress = True + except: # sink all errors here pylint: disable=bare-except + # Try this one again, if progress was made on a possible dependency + remains.append(name) + if remains: + # There are modules that won't import in any order. + # Print all the errors as we can't determine root cause. + for name in remains: + try: + _Import(name) + except ImportError as e: + print 'Failed importing', name, ':', e + exit(1) + # Now scan all the found modules one more time. + # This happens after all imports, in case any imports register scan hooks. + for module in modules: + _ScanModule(module) |