mirror of
https://github.com/janeczku/calibre-web
synced 2024-12-27 02:20:31 +00:00
245 lines
6.9 KiB
Python
245 lines
6.9 KiB
Python
""":mod:`wand.resource` --- Global resource management
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
There is the global resource to manage in MagickWand API. This module
|
|
implements automatic global resource management through reference counting.
|
|
|
|
"""
|
|
import contextlib
|
|
import ctypes
|
|
import warnings
|
|
|
|
from .api import library
|
|
from .compat import string_type
|
|
from .exceptions import TYPE_MAP, WandException
|
|
|
|
|
|
__all__ = ('genesis', 'terminus', 'increment_refcount', 'decrement_refcount',
|
|
'Resource', 'DestroyedResourceError')
|
|
|
|
|
|
def genesis():
|
|
"""Instantiates the MagickWand API.
|
|
|
|
.. warning::
|
|
|
|
Don't call this function directly. Use :func:`increment_refcount()` and
|
|
:func:`decrement_refcount()` functions instead.
|
|
|
|
"""
|
|
library.MagickWandGenesis()
|
|
|
|
|
|
def terminus():
|
|
"""Cleans up the MagickWand API.
|
|
|
|
.. warning::
|
|
|
|
Don't call this function directly. Use :func:`increment_refcount()` and
|
|
:func:`decrement_refcount()` functions instead.
|
|
|
|
"""
|
|
library.MagickWandTerminus()
|
|
|
|
|
|
#: (:class:`numbers.Integral`) The internal integer value that maintains
|
|
#: the number of referenced objects.
|
|
#:
|
|
#: .. warning::
|
|
#:
|
|
#: Don't touch this global variable. Use :func:`increment_refcount()` and
|
|
#: :func:`decrement_refcount()` functions instead.
|
|
#:
|
|
reference_count = 0
|
|
|
|
|
|
def increment_refcount():
|
|
"""Increments the :data:`reference_count` and instantiates the MagickWand
|
|
API if it is the first use.
|
|
|
|
"""
|
|
global reference_count
|
|
if reference_count:
|
|
reference_count += 1
|
|
else:
|
|
genesis()
|
|
reference_count = 1
|
|
|
|
|
|
def decrement_refcount():
|
|
"""Decrements the :data:`reference_count` and cleans up the MagickWand
|
|
API if it will be no more used.
|
|
|
|
"""
|
|
global reference_count
|
|
if not reference_count:
|
|
raise RuntimeError('wand.resource.reference_count is already zero')
|
|
reference_count -= 1
|
|
if not reference_count:
|
|
terminus()
|
|
|
|
|
|
class Resource(object):
|
|
"""Abstract base class for MagickWand object that requires resource
|
|
management. Its all subclasses manage the resource semiautomatically
|
|
and support :keyword:`with` statement as well::
|
|
|
|
with Resource() as resource:
|
|
# use the resource...
|
|
pass
|
|
|
|
It doesn't implement constructor by itself, so subclasses should
|
|
implement it. Every constructor should assign the pointer of its
|
|
resource data into :attr:`resource` attribute inside of :keyword:`with`
|
|
:meth:`allocate()` context. For example::
|
|
|
|
class Pizza(Resource):
|
|
'''My pizza yummy.'''
|
|
|
|
def __init__(self):
|
|
with self.allocate():
|
|
self.resource = library.NewPizza()
|
|
|
|
.. versionadded:: 0.1.2
|
|
|
|
"""
|
|
|
|
#: (:class:`ctypes.CFUNCTYPE`) The :mod:`ctypes` predicate function
|
|
#: that returns whether the given pointer (that contains a resource data
|
|
#: usuaully) is a valid resource.
|
|
#:
|
|
#: .. note::
|
|
#:
|
|
#: It is an abstract attribute that has to be implemented
|
|
#: in the subclass.
|
|
c_is_resource = NotImplemented
|
|
|
|
#: (:class:`ctypes.CFUNCTYPE`) The :mod:`ctypes` function that destroys
|
|
#: the :attr:`resource`.
|
|
#:
|
|
#: .. note::
|
|
#:
|
|
#: It is an abstract attribute that has to be implemented
|
|
#: in the subclass.
|
|
c_destroy_resource = NotImplemented
|
|
|
|
#: (:class:`ctypes.CFUNCTYPE`) The :mod:`ctypes` function that gets
|
|
#: an exception from the :attr:`resource`.
|
|
#:
|
|
#: .. note::
|
|
#:
|
|
#: It is an abstract attribute that has to be implemented
|
|
#: in the subclass.
|
|
c_get_exception = NotImplemented
|
|
|
|
#: (:class:`ctypes.CFUNCTYPE`) The :mod:`ctypes` function that clears
|
|
#: an exception of the :attr:`resource`.
|
|
#:
|
|
#: .. note::
|
|
#:
|
|
#: It is an abstract attribute that has to be implemented
|
|
#: in the subclass.
|
|
c_clear_exception = NotImplemented
|
|
|
|
@property
|
|
def resource(self):
|
|
"""Internal pointer to the resource instance. It may raise
|
|
:exc:`DestroyedResourceError` when the resource has destroyed already.
|
|
|
|
"""
|
|
if getattr(self, 'c_resource', None) is None:
|
|
raise DestroyedResourceError(repr(self) + ' is destroyed already')
|
|
return self.c_resource
|
|
|
|
@resource.setter
|
|
def resource(self, resource):
|
|
# Delete the existing resource if there is one
|
|
if getattr(self, 'c_resource', None):
|
|
self.destroy()
|
|
|
|
if self.c_is_resource(resource):
|
|
self.c_resource = resource
|
|
else:
|
|
raise TypeError(repr(resource) + ' is an invalid resource')
|
|
increment_refcount()
|
|
|
|
@resource.deleter
|
|
def resource(self):
|
|
self.c_destroy_resource(self.resource)
|
|
self.c_resource = None
|
|
|
|
@contextlib.contextmanager
|
|
def allocate(self):
|
|
"""Allocates the memory for the resource explicitly. Its subclasses
|
|
should assign the created resource into :attr:`resource` attribute
|
|
inside of this context. For example::
|
|
|
|
with resource.allocate():
|
|
resource.resource = library.NewResource()
|
|
|
|
"""
|
|
increment_refcount()
|
|
try:
|
|
yield self
|
|
except:
|
|
decrement_refcount()
|
|
raise
|
|
|
|
def destroy(self):
|
|
"""Cleans up the resource explicitly. If you use the resource in
|
|
:keyword:`with` statement, it was called implicitly so have not to
|
|
call it.
|
|
|
|
"""
|
|
del self.resource
|
|
decrement_refcount()
|
|
|
|
def get_exception(self):
|
|
"""Gets a current exception instance.
|
|
|
|
:returns: a current exception. it can be ``None`` as well if any
|
|
errors aren't occurred
|
|
:rtype: :class:`wand.exceptions.WandException`
|
|
|
|
"""
|
|
severity = ctypes.c_int()
|
|
desc = self.c_get_exception(self.resource, ctypes.byref(severity))
|
|
if severity.value == 0:
|
|
return
|
|
self.c_clear_exception(self.wand)
|
|
exc_cls = TYPE_MAP[severity.value]
|
|
message = desc.value
|
|
if not isinstance(message, string_type):
|
|
message = message.decode(errors='replace')
|
|
return exc_cls(message)
|
|
|
|
def raise_exception(self, stacklevel=1):
|
|
"""Raises an exception or warning if it has occurred."""
|
|
e = self.get_exception()
|
|
if isinstance(e, Warning):
|
|
warnings.warn(e, stacklevel=stacklevel + 1)
|
|
elif isinstance(e, Exception):
|
|
raise e
|
|
|
|
def __enter__(self):
|
|
return self
|
|
|
|
def __exit__(self, type, value, traceback):
|
|
self.destroy()
|
|
|
|
def __del__(self):
|
|
try:
|
|
self.destroy()
|
|
except DestroyedResourceError:
|
|
pass
|
|
|
|
|
|
class DestroyedResourceError(WandException, ReferenceError, AttributeError):
|
|
"""An error that rises when some code tries access to an already
|
|
destroyed resource.
|
|
|
|
.. versionchanged:: 0.3.0
|
|
It becomes a subtype of :exc:`wand.exceptions.WandException`.
|
|
|
|
"""
|