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1165 lines (958 loc) · 38.3 KB
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"""Core implementation of import.
This module is NOT meant to be directly imported! It has been designed such
that it can be bootstrapped into Python as the implementation of import. As
such it requires the injection of specific modules and attributes in order to
work. One should use importlib as the public-facing version of this module.
"""
#
# IMPORTANT: Whenever making changes to this module, be sure to run
# a top-level make in order to get the frozen version of the module
# updated. Not doing so will result in the Makefile to fail for
# all others who don't have a ./python around to freeze the module
# in the early stages of compilation.
#
# See importlib._setup() for what is injected into the global namespace.
# When editing this code be aware that code executed at import time CANNOT
# reference any injected objects! This includes not only global code but also
# anything specified at the class level.
# Bootstrap-related code ######################################################
_bootstrap_external = None
def _wrap(new, old):
"""Simple substitute for functools.update_wrapper."""
for replace in ['__module__', '__name__', '__qualname__', '__doc__']:
if hasattr(old, replace):
setattr(new, replace, getattr(old, replace))
new.__dict__.update(old.__dict__)
def _new_module(name):
return type(sys)(name)
# Module-level locking ########################################################
# A dict mapping module names to weakrefs of _ModuleLock instances
# Dictionary protected by the global import lock
_module_locks = {}
# A dict mapping thread ids to _ModuleLock instances
_blocking_on = {}
class _DeadlockError(RuntimeError):
pass
class _ModuleLock:
"""A recursive lock implementation which is able to detect deadlocks
(e.g. thread 1 trying to take locks A then B, and thread 2 trying to
take locks B then A).
"""
def __init__(self, name):
self.lock = _thread.allocate_lock()
self.wakeup = _thread.allocate_lock()
self.name = name
self.owner = None
self.count = 0
self.waiters = 0
def has_deadlock(self):
# Deadlock avoidance for concurrent circular imports.
me = _thread.get_ident()
tid = self.owner
while True:
lock = _blocking_on.get(tid)
if lock is None:
return False
tid = lock.owner
if tid == me:
return True
def acquire(self):
"""
Acquire the module lock. If a potential deadlock is detected,
a _DeadlockError is raised.
Otherwise, the lock is always acquired and True is returned.
"""
tid = _thread.get_ident()
_blocking_on[tid] = self
try:
while True:
with self.lock:
if self.count == 0 or self.owner == tid:
self.owner = tid
self.count += 1
return True
if self.has_deadlock():
raise _DeadlockError('deadlock detected by %r' % self)
if self.wakeup.acquire(False):
self.waiters += 1
# Wait for a release() call
self.wakeup.acquire()
self.wakeup.release()
finally:
del _blocking_on[tid]
def release(self):
tid = _thread.get_ident()
with self.lock:
if self.owner != tid:
raise RuntimeError('cannot release un-acquired lock')
assert self.count > 0
self.count -= 1
if self.count == 0:
self.owner = None
if self.waiters:
self.waiters -= 1
self.wakeup.release()
def __repr__(self):
return '_ModuleLock({!r}) at {}'.format(self.name, id(self))
class _DummyModuleLock:
"""A simple _ModuleLock equivalent for Python builds without
multi-threading support."""
def __init__(self, name):
self.name = name
self.count = 0
def acquire(self):
self.count += 1
return True
def release(self):
if self.count == 0:
raise RuntimeError('cannot release un-acquired lock')
self.count -= 1
def __repr__(self):
return '_DummyModuleLock({!r}) at {}'.format(self.name, id(self))
class _ModuleLockManager:
def __init__(self, name):
self._name = name
self._lock = None
def __enter__(self):
self._lock = _get_module_lock(self._name)
self._lock.acquire()
def __exit__(self, *args, **kwargs):
self._lock.release()
# The following two functions are for consumption by Python/import.c.
def _get_module_lock(name):
"""Get or create the module lock for a given module name.
Acquire/release internally the global import lock to protect
_module_locks."""
_imp.acquire_lock()
try:
try:
lock = _module_locks[name]()
except KeyError:
lock = None
if lock is None:
if _thread is None:
lock = _DummyModuleLock(name)
else:
lock = _ModuleLock(name)
def cb(ref, name=name):
_imp.acquire_lock()
try:
# bpo-31070: Check if another thread created a new lock
# after the previous lock was destroyed
# but before the weakref callback was called.
if _module_locks.get(name) is ref:
del _module_locks[name]
finally:
_imp.release_lock()
_module_locks[name] = _weakref.ref(lock, cb)
finally:
_imp.release_lock()
return lock
def _lock_unlock_module(name):
"""Acquires then releases the module lock for a given module name.
This is used to ensure a module is completely initialized, in the
event it is being imported by another thread.
"""
lock = _get_module_lock(name)
try:
lock.acquire()
except _DeadlockError:
# Concurrent circular import, we'll accept a partially initialized
# module object.
pass
else:
lock.release()
# Frame stripping magic ###############################################
def _call_with_frames_removed(f, *args, **kwds):
"""remove_importlib_frames in import.c will always remove sequences
of importlib frames that end with a call to this function
Use it instead of a normal call in places where including the importlib
frames introduces unwanted noise into the traceback (e.g. when executing
module code)
"""
return f(*args, **kwds)
def _verbose_message(message, *args, verbosity=1):
"""Print the message to stderr if -v/PYTHONVERBOSE is turned on."""
if sys.flags.verbose >= verbosity:
if not message.startswith(('#', 'import ')):
message = '# ' + message
print(message.format(*args), file=sys.stderr)
def _requires_builtin(fxn):
"""Decorator to verify the named module is built-in."""
def _requires_builtin_wrapper(self, fullname):
if fullname not in sys.builtin_module_names:
raise ImportError('{!r} is not a built-in module'.format(fullname),
name=fullname)
return fxn(self, fullname)
_wrap(_requires_builtin_wrapper, fxn)
return _requires_builtin_wrapper
def _requires_frozen(fxn):
"""Decorator to verify the named module is frozen."""
def _requires_frozen_wrapper(self, fullname):
if not _imp.is_frozen(fullname):
raise ImportError('{!r} is not a frozen module'.format(fullname),
name=fullname)
return fxn(self, fullname)
_wrap(_requires_frozen_wrapper, fxn)
return _requires_frozen_wrapper
# Typically used by loader classes as a method replacement.
def _load_module_shim(self, fullname):
"""Load the specified module into sys.modules and return it.
This method is deprecated. Use loader.exec_module instead.
"""
spec = spec_from_loader(fullname, self)
if fullname in sys.modules:
module = sys.modules[fullname]
_exec(spec, module)
return sys.modules[fullname]
else:
return _load(spec)
# Module specifications #######################################################
def _module_repr(module):
# The implementation of ModuleType.__repr__().
loader = getattr(module, '__loader__', None)
if hasattr(loader, 'module_repr'):
# As soon as BuiltinImporter, FrozenImporter, and NamespaceLoader
# drop their implementations for module_repr. we can add a
# deprecation warning here.
try:
return loader.module_repr(module)
except Exception:
pass
try:
spec = module.__spec__
except AttributeError:
pass
else:
if spec is not None:
return _module_repr_from_spec(spec)
# We could use module.__class__.__name__ instead of 'module' in the
# various repr permutations.
try:
name = module.__name__
except AttributeError:
name = '?'
try:
filename = module.__file__
except AttributeError:
if loader is None:
return '<module {!r}>'.format(name)
else:
return '<module {!r} ({!r})>'.format(name, loader)
else:
return '<module {!r} from {!r}>'.format(name, filename)
class _installed_safely:
def __init__(self, module):
self._module = module
self._spec = module.__spec__
def __enter__(self):
# This must be done before putting the module in sys.modules
# (otherwise an optimization shortcut in import.c becomes
# wrong)
self._spec._initializing = True
sys.modules[self._spec.name] = self._module
def __exit__(self, *args):
try:
spec = self._spec
if any(arg is not None for arg in args):
try:
del sys.modules[spec.name]
except KeyError:
pass
else:
_verbose_message('import {!r} # {!r}', spec.name, spec.loader)
finally:
self._spec._initializing = False
class ModuleSpec:
"""The specification for a module, used for loading.
A module's spec is the source for information about the module. For
data associated with the module, including source, use the spec's
loader.
`name` is the absolute name of the module. `loader` is the loader
to use when loading the module. `parent` is the name of the
package the module is in. The parent is derived from the name.
`is_package` determines if the module is considered a package or
not. On modules this is reflected by the `__path__` attribute.
`origin` is the specific location used by the loader from which to
load the module, if that information is available. When filename is
set, origin will match.
`has_location` indicates that a spec's "origin" reflects a location.
When this is True, `__file__` attribute of the module is set.
`cached` is the location of the cached bytecode file, if any. It
corresponds to the `__cached__` attribute.
`submodule_search_locations` is the sequence of path entries to
search when importing submodules. If set, is_package should be
True--and False otherwise.
Packages are simply modules that (may) have submodules. If a spec
has a non-None value in `submodule_search_locations`, the import
system will consider modules loaded from the spec as packages.
Only finders (see importlib.abc.MetaPathFinder and
importlib.abc.PathEntryFinder) should modify ModuleSpec instances.
"""
def __init__(self, name, loader, *, origin=None, loader_state=None,
is_package=None):
self.name = name
self.loader = loader
self.origin = origin
self.loader_state = loader_state
self.submodule_search_locations = [] if is_package else None
# file-location attributes
self._set_fileattr = False
self._cached = None
def __repr__(self):
args = ['name={!r}'.format(self.name),
'loader={!r}'.format(self.loader)]
if self.origin is not None:
args.append('origin={!r}'.format(self.origin))
if self.submodule_search_locations is not None:
args.append('submodule_search_locations={}'
.format(self.submodule_search_locations))
return '{}({})'.format(self.__class__.__name__, ', '.join(args))
def __eq__(self, other):
smsl = self.submodule_search_locations
try:
return (self.name == other.name and
self.loader == other.loader and
self.origin == other.origin and
smsl == other.submodule_search_locations and
self.cached == other.cached and
self.has_location == other.has_location)
except AttributeError:
return False
@property
def cached(self):
if self._cached is None:
if self.origin is not None and self._set_fileattr:
if _bootstrap_external is None:
raise NotImplementedError
self._cached = _bootstrap_external._get_cached(self.origin)
return self._cached
@cached.setter
def cached(self, cached):
self._cached = cached
@property
def parent(self):
"""The name of the module's parent."""
if self.submodule_search_locations is None:
return self.name.rpartition('.')[0]
else:
return self.name
@property
def has_location(self):
return self._set_fileattr
@has_location.setter
def has_location(self, value):
self._set_fileattr = bool(value)
def spec_from_loader(name, loader, *, origin=None, is_package=None):
"""Return a module spec based on various loader methods."""
if hasattr(loader, 'get_filename'):
if _bootstrap_external is None:
raise NotImplementedError
spec_from_file_location = _bootstrap_external.spec_from_file_location
if is_package is None:
return spec_from_file_location(name, loader=loader)
search = [] if is_package else None
return spec_from_file_location(name, loader=loader,
submodule_search_locations=search)
if is_package is None:
if hasattr(loader, 'is_package'):
try:
is_package = loader.is_package(name)
except ImportError:
is_package = None # aka, undefined
else:
# the default
is_package = False
return ModuleSpec(name, loader, origin=origin, is_package=is_package)
def _spec_from_module(module, loader=None, origin=None):
# This function is meant for use in _setup().
try:
spec = module.__spec__
except AttributeError:
pass
else:
if spec is not None:
return spec
name = module.__name__
if loader is None:
try:
loader = module.__loader__
except AttributeError:
# loader will stay None.
pass
try:
location = module.__file__
except AttributeError:
location = None
if origin is None:
if location is None:
try:
origin = loader._ORIGIN
except AttributeError:
origin = None
else:
origin = location
try:
cached = module.__cached__
except AttributeError:
cached = None
try:
submodule_search_locations = list(module.__path__)
except AttributeError:
submodule_search_locations = None
spec = ModuleSpec(name, loader, origin=origin)
spec._set_fileattr = False if location is None else True
spec.cached = cached
spec.submodule_search_locations = submodule_search_locations
return spec
def _init_module_attrs(spec, module, *, override=False):
# The passed-in module may be not support attribute assignment,
# in which case we simply don't set the attributes.
# __name__
if (override or getattr(module, '__name__', None) is None):
try:
module.__name__ = spec.name
except AttributeError:
pass
# __loader__
if override or getattr(module, '__loader__', None) is None:
loader = spec.loader
if loader is None:
# A backward compatibility hack.
if spec.submodule_search_locations is not None:
if _bootstrap_external is None:
raise NotImplementedError
_NamespaceLoader = _bootstrap_external._NamespaceLoader
loader = _NamespaceLoader.__new__(_NamespaceLoader)
loader._path = spec.submodule_search_locations
spec.loader = loader
# While the docs say that module.__file__ is not set for
# built-in modules, and the code below will avoid setting it if
# spec.has_location is false, this is incorrect for namespace
# packages. Namespace packages have no location, but their
# __spec__.origin is None, and thus their module.__file__
# should also be None for consistency. While a bit of a hack,
# this is the best place to ensure this consistency.
#
# See # https://docs.python.org/3/library/importlib.html#importlib.abc.Loader.load_module
# and bpo-32305
module.__file__ = None
try:
module.__loader__ = loader
except AttributeError:
pass
# __package__
if override or getattr(module, '__package__', None) is None:
try:
module.__package__ = spec.parent
except AttributeError:
pass
# __spec__
try:
module.__spec__ = spec
except AttributeError:
pass
# __path__
if override or getattr(module, '__path__', None) is None:
if spec.submodule_search_locations is not None:
try:
module.__path__ = spec.submodule_search_locations
except AttributeError:
pass
# __file__/__cached__
if spec.has_location:
if override or getattr(module, '__file__', None) is None:
try:
module.__file__ = spec.origin
except AttributeError:
pass
if override or getattr(module, '__cached__', None) is None:
if spec.cached is not None:
try:
module.__cached__ = spec.cached
except AttributeError:
pass
return module
def module_from_spec(spec):
"""Create a module based on the provided spec."""
# Typically loaders will not implement create_module().
module = None
if hasattr(spec.loader, 'create_module'):
# If create_module() returns `None` then it means default
# module creation should be used.
module = spec.loader.create_module(spec)
elif hasattr(spec.loader, 'exec_module'):
raise ImportError('loaders that define exec_module() '
'must also define create_module()')
if module is None:
module = _new_module(spec.name)
_init_module_attrs(spec, module)
return module
def _module_repr_from_spec(spec):
"""Return the repr to use for the module."""
# We mostly replicate _module_repr() using the spec attributes.
name = '?' if spec.name is None else spec.name
if spec.origin is None:
if spec.loader is None:
return '<module {!r}>'.format(name)
else:
return '<module {!r} ({!r})>'.format(name, spec.loader)
else:
if spec.has_location:
return '<module {!r} from {!r}>'.format(name, spec.origin)
else:
return '<module {!r} ({})>'.format(spec.name, spec.origin)
# Used by importlib.reload() and _load_module_shim().
def _exec(spec, module):
"""Execute the spec's specified module in an existing module's namespace."""
name = spec.name
with _ModuleLockManager(name):
if sys.modules.get(name) is not module:
msg = 'module {!r} not in sys.modules'.format(name)
raise ImportError(msg, name=name)
if spec.loader is None:
if spec.submodule_search_locations is None:
raise ImportError('missing loader', name=spec.name)
# namespace package
_init_module_attrs(spec, module, override=True)
return module
_init_module_attrs(spec, module, override=True)
if not hasattr(spec.loader, 'exec_module'):
# (issue19713) Once BuiltinImporter and ExtensionFileLoader
# have exec_module() implemented, we can add a deprecation
# warning here.
spec.loader.load_module(name)
else:
spec.loader.exec_module(module)
return sys.modules[name]
def _load_backward_compatible(spec):
# (issue19713) Once BuiltinImporter and ExtensionFileLoader
# have exec_module() implemented, we can add a deprecation
# warning here.
spec.loader.load_module(spec.name)
# The module must be in sys.modules at this point!
module = sys.modules[spec.name]
if getattr(module, '__loader__', None) is None:
try:
module.__loader__ = spec.loader
except AttributeError:
pass
if getattr(module, '__package__', None) is None:
try:
# Since module.__path__ may not line up with
# spec.submodule_search_paths, we can't necessarily rely
# on spec.parent here.
module.__package__ = module.__name__
if not hasattr(module, '__path__'):
module.__package__ = spec.name.rpartition('.')[0]
except AttributeError:
pass
if getattr(module, '__spec__', None) is None:
try:
module.__spec__ = spec
except AttributeError:
pass
return module
def _load_unlocked(spec):
# A helper for direct use by the import system.
if spec.loader is not None:
# not a namespace package
if not hasattr(spec.loader, 'exec_module'):
return _load_backward_compatible(spec)
module = module_from_spec(spec)
with _installed_safely(module):
if spec.loader is None:
if spec.submodule_search_locations is None:
raise ImportError('missing loader', name=spec.name)
# A namespace package so do nothing.
else:
spec.loader.exec_module(module)
# We don't ensure that the import-related module attributes get
# set in the sys.modules replacement case. Such modules are on
# their own.
return sys.modules[spec.name]
# A method used during testing of _load_unlocked() and by
# _load_module_shim().
def _load(spec):
"""Return a new module object, loaded by the spec's loader.
The module is not added to its parent.
If a module is already in sys.modules, that existing module gets
clobbered.
"""
with _ModuleLockManager(spec.name):
return _load_unlocked(spec)
# Loaders #####################################################################
class BuiltinImporter:
"""Meta path import for built-in modules.
All methods are either class or static methods to avoid the need to
instantiate the class.
"""
@staticmethod
def module_repr(module):
"""Return repr for the module.
The method is deprecated. The import machinery does the job itself.
"""
return '<module {!r} (built-in)>'.format(module.__name__)
@classmethod
def find_spec(cls, fullname, path=None, target=None):
if path is not None:
return None
if _imp.is_builtin(fullname):
return spec_from_loader(fullname, cls, origin='built-in')
else:
return None
@classmethod
def find_module(cls, fullname, path=None):
"""Find the built-in module.
If 'path' is ever specified then the search is considered a failure.
This method is deprecated. Use find_spec() instead.
"""
spec = cls.find_spec(fullname, path)
return spec.loader if spec is not None else None
@classmethod
def create_module(self, spec):
"""Create a built-in module"""
if spec.name not in sys.builtin_module_names:
raise ImportError('{!r} is not a built-in module'.format(spec.name),
name=spec.name)
return _call_with_frames_removed(_imp.create_builtin, spec)
@classmethod
def exec_module(self, module):
"""Exec a built-in module"""
_call_with_frames_removed(_imp.exec_builtin, module)
@classmethod
@_requires_builtin
def get_code(cls, fullname):
"""Return None as built-in modules do not have code objects."""
return None
@classmethod
@_requires_builtin
def get_source(cls, fullname):
"""Return None as built-in modules do not have source code."""
return None
@classmethod
@_requires_builtin
def is_package(cls, fullname):
"""Return False as built-in modules are never packages."""
return False
load_module = classmethod(_load_module_shim)
class FrozenImporter:
"""Meta path import for frozen modules.
All methods are either class or static methods to avoid the need to
instantiate the class.
"""
@staticmethod
def module_repr(m):
"""Return repr for the module.
The method is deprecated. The import machinery does the job itself.
"""
return '<module {!r} (frozen)>'.format(m.__name__)
@classmethod
def find_spec(cls, fullname, path=None, target=None):
if _imp.is_frozen(fullname):
return spec_from_loader(fullname, cls, origin='frozen')
else:
return None
@classmethod
def find_module(cls, fullname, path=None):
"""Find a frozen module.
This method is deprecated. Use find_spec() instead.
"""
return cls if _imp.is_frozen(fullname) else None
@classmethod
def create_module(cls, spec):
"""Use default semantics for module creation."""
@staticmethod
def exec_module(module):
name = module.__spec__.name
if not _imp.is_frozen(name):
raise ImportError('{!r} is not a frozen module'.format(name),
name=name)
code = _call_with_frames_removed(_imp.get_frozen_object, name)
exec(code, module.__dict__)
@classmethod
def load_module(cls, fullname):
"""Load a frozen module.
This method is deprecated. Use exec_module() instead.
"""
return _load_module_shim(cls, fullname)
@classmethod
@_requires_frozen
def get_code(cls, fullname):
"""Return the code object for the frozen module."""
return _imp.get_frozen_object(fullname)
@classmethod
@_requires_frozen
def get_source(cls, fullname):
"""Return None as frozen modules do not have source code."""
return None
@classmethod
@_requires_frozen
def is_package(cls, fullname):
"""Return True if the frozen module is a package."""
return _imp.is_frozen_package(fullname)
# Import itself ###############################################################
class _ImportLockContext:
"""Context manager for the import lock."""
def __enter__(self):
"""Acquire the import lock."""
_imp.acquire_lock()
def __exit__(self, exc_type, exc_value, exc_traceback):
"""Release the import lock regardless of any raised exceptions."""
_imp.release_lock()
def _resolve_name(name, package, level):
"""Resolve a relative module name to an absolute one."""
bits = package.rsplit('.', level - 1)
if len(bits) < level:
raise ValueError('attempted relative import beyond top-level package')
base = bits[0]
return '{}.{}'.format(base, name) if name else base
def _find_spec_legacy(finder, name, path):
# This would be a good place for a DeprecationWarning if
# we ended up going that route.
loader = finder.find_module(name, path)
if loader is None:
return None
return spec_from_loader(name, loader)
def _find_spec(name, path, target=None):
"""Find a module's spec."""
meta_path = sys.meta_path
if meta_path is None:
# PyImport_Cleanup() is running or has been called.
raise ImportError("sys.meta_path is None, Python is likely "
"shutting down")
if not meta_path:
_warnings.warn('sys.meta_path is empty', ImportWarning)
# We check sys.modules here for the reload case. While a passed-in
# target will usually indicate a reload there is no guarantee, whereas
# sys.modules provides one.
is_reload = name in sys.modules
for finder in meta_path:
with _ImportLockContext():
try:
find_spec = finder.find_spec
except AttributeError:
spec = _find_spec_legacy(finder, name, path)
if spec is None:
continue
else:
spec = find_spec(name, path, target)
if spec is not None:
# The parent import may have already imported this module.
if not is_reload and name in sys.modules:
module = sys.modules[name]
try:
__spec__ = module.__spec__
except AttributeError:
# We use the found spec since that is the one that
# we would have used if the parent module hadn't
# beaten us to the punch.
return spec
else:
if __spec__ is None:
return spec
else:
return __spec__
else:
return spec
else:
return None
def _sanity_check(name, package, level):
"""Verify arguments are "sane"."""
if not isinstance(name, str):
raise TypeError('module name must be str, not {}'.format(type(name)))
if level < 0:
raise ValueError('level must be >= 0')
if level > 0:
if not isinstance(package, str):
raise TypeError('__package__ not set to a string')
elif not package:
raise ImportError('attempted relative import with no known parent '
'package')
if not name and level == 0:
raise ValueError('Empty module name')
_ERR_MSG_PREFIX = 'No module named '
_ERR_MSG = _ERR_MSG_PREFIX + '{!r}'
def _find_and_load_unlocked(name, import_):
path = None
parent = name.rpartition('.')[0]
if parent:
if parent not in sys.modules:
_call_with_frames_removed(import_, parent)
# Crazy side-effects!
if name in sys.modules:
return sys.modules[name]
parent_module = sys.modules[parent]
try:
path = parent_module.__path__
except AttributeError:
msg = (_ERR_MSG + '; {!r} is not a package').format(name, parent)
raise ModuleNotFoundError(msg, name=name) from None
spec = _find_spec(name, path)
if spec is None:
raise ModuleNotFoundError(_ERR_MSG.format(name), name=name)
else:
module = _load_unlocked(spec)
if parent:
# Set the module as an attribute on its parent.
parent_module = sys.modules[parent]
setattr(parent_module, name.rpartition('.')[2], module)
return module
_NEEDS_LOADING = object()
def _find_and_load(name, import_):
"""Find and load the module."""
with _ModuleLockManager(name):
module = sys.modules.get(name, _NEEDS_LOADING)
if module is _NEEDS_LOADING:
return _find_and_load_unlocked(name, import_)
if module is None:
message = ('import of {} halted; '
'None in sys.modules'.format(name))
raise ModuleNotFoundError(message, name=name)
_lock_unlock_module(name)
return module
def _gcd_import(name, package=None, level=0):
"""Import and return the module based on its name, the package the call is
being made from, and the level adjustment.
This function represents the greatest common denominator of functionality
between import_module and __import__. This includes setting __package__ if
the loader did not.