# Copyright 2020 Canonical Ltd.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""The Operator Framework infrastructure."""
import collections
import collections.abc
import inspect
import keyword
import logging
import marshal
import os
import pathlib
import pdb
import re
import sys
import types
import weakref
from ops import charm
from ops.storage import (
NoSnapshotError,
SQLiteStorage,
)
logger = logging.getLogger(__name__)
[docs]class Handle:
"""Handle defines a name for an object in the form of a hierarchical path.
The provided parent is the object (or that object's handle) that this handle
sits under, or None if the object identified by this handle stands by itself
as the root of its own hierarchy.
The handle kind is a string that defines a namespace so objects with the
same parent and kind will have unique keys.
The handle key is a string uniquely identifying the object. No other objects
under the same parent and kind may have the same key.
"""
def __init__(self, parent, kind, key):
if parent and not isinstance(parent, Handle):
parent = parent.handle
self._parent = parent
self._kind = kind
self._key = key
if parent:
if key:
self._path = "{}/{}[{}]".format(parent, kind, key)
else:
self._path = "{}/{}".format(parent, kind)
else:
if key:
self._path = "{}[{}]".format(kind, key)
else:
self._path = "{}".format(kind)
[docs] def nest(self, kind, key):
"""Create a new handle as child of the current one."""
return Handle(self, kind, key)
def __hash__(self):
return hash((self.parent, self.kind, self.key))
def __eq__(self, other):
return (self.parent, self.kind, self.key) == (other.parent, other.kind, other.key)
def __str__(self):
return self.path
@property
def parent(self):
"""Return own parent handle."""
return self._parent
@property
def kind(self):
"""Return the handle's kind."""
return self._kind
@property
def key(self):
"""Return the handle's key."""
return self._key
@property
def path(self):
"""Return the handle's path."""
return self._path
[docs] @classmethod
def from_path(cls, path):
"""Build a handle from the indicated path."""
handle = None
for pair in path.split("/"):
pair = pair.split("[")
good = False
if len(pair) == 1:
kind, key = pair[0], None
good = True
elif len(pair) == 2:
kind, key = pair
if key and key[-1] == ']':
key = key[:-1]
good = True
if not good:
raise RuntimeError("attempted to restore invalid handle path {}".format(path))
handle = Handle(handle, kind, key)
return handle
[docs]class EventBase:
"""The base for all the different Events.
Inherit this and override 'snapshot' and 'restore' methods to build a custom event.
"""
def __init__(self, handle):
self.handle = handle
self.deferred = False
def __repr__(self):
return "<%s via %s>" % (self.__class__.__name__, self.handle)
[docs] def defer(self):
"""Defer the event to the future.
Deferring an event from a handler puts that handler into a queue, to be
called again the next time the charm is invoked. This invocation may be
the result of an action, or any event other than metric events. The
queue of events will be dispatched before the new event is processed.
From the above you may deduce, but it's important to point out:
* ``defer()`` does not interrupt the execution of the current event
handler. In almost all cases, a call to ``defer()`` should be followed
by an explicit ``return`` from the handler;
* the re-execution of the deferred event handler starts from the top of
the handler method (not where defer was called);
* only the handlers that actually called ``defer()`` are called again
(that is: despite talking about “deferring an event” it is actually
the handler/event combination that is deferred); and
* any deferred events get processed before the event (or action) that
caused the current invocation of the charm.
The general desire to call ``defer()`` happens when some precondition
isn't yet met. However, care should be exercised as to whether it is
better to defer this event so that you see it again, or whether it is
better to just wait for the event that indicates the precondition has
been met.
For example, if ``config-changed`` is fired, and you are waiting for
different config, there is no reason to defer the event because there
will be a *different* ``config-changed`` event when the config actually
changes, rather than checking to see if maybe config has changed prior
to every other event that occurs.
Similarly, if you need 2 events to occur before you are ready to
proceed (say event A and B). When you see event A, you could chose to
``defer()`` it because you haven't seen B yet. However, that leads to:
1. event A fires, calls defer()
2. event B fires, event A handler is called first, still hasn't seen B
happen, so is deferred again. Then B happens, which progresses since
it has seen A.
3. At some future time, event C happens, which also checks if A can
proceed.
"""
logger.debug("Deferring %s.", self)
self.deferred = True
[docs] def snapshot(self):
"""Return the snapshot data that should be persisted.
Subclasses must override to save any custom state.
"""
return None
[docs] def restore(self, snapshot):
"""Restore the value state from the given snapshot.
Subclasses must override to restore their custom state.
"""
self.deferred = False
[docs]class EventSource:
"""EventSource wraps an event type with a descriptor to facilitate observing and emitting.
It is generally used as:
class SomethingHappened(EventBase):
pass
class SomeObject(Object):
something_happened = EventSource(SomethingHappened)
With that, instances of that type will offer the someobj.something_happened
attribute which is a BoundEvent and may be used to emit and observe the event.
"""
def __init__(self, event_type):
if not isinstance(event_type, type) or not issubclass(event_type, EventBase):
raise RuntimeError(
'Event requires a subclass of EventBase as an argument, got {}'.format(event_type))
self.event_type = event_type
self.event_kind = None
self.emitter_type = None
def _set_name(self, emitter_type, event_kind):
if self.event_kind is not None:
raise RuntimeError(
'EventSource({}) reused as {}.{} and {}.{}'.format(
self.event_type.__name__,
self.emitter_type.__name__,
self.event_kind,
emitter_type.__name__,
event_kind,
))
self.event_kind = event_kind
self.emitter_type = emitter_type
def __get__(self, emitter, emitter_type=None):
if emitter is None:
return self
# Framework might not be available if accessed as CharmClass.on.event
# rather than charm_instance.on.event, but in that case it couldn't be
# emitted anyway, so there's no point to registering it.
framework = getattr(emitter, 'framework', None)
if framework is not None:
framework.register_type(self.event_type, emitter, self.event_kind)
return BoundEvent(emitter, self.event_type, self.event_kind)
[docs]class BoundEvent:
"""Event bound to an Object."""
def __repr__(self):
return '<BoundEvent {} bound to {}.{} at {}>'.format(
self.event_type.__name__,
type(self.emitter).__name__,
self.event_kind,
hex(id(self)),
)
def __init__(self, emitter, event_type, event_kind):
self.emitter = emitter
self.event_type = event_type
self.event_kind = event_kind
[docs] def emit(self, *args, **kwargs):
"""Emit event to all registered observers.
The current storage state is committed before and after each observer is notified.
"""
framework = self.emitter.framework
key = framework._next_event_key()
event = self.event_type(Handle(self.emitter, self.event_kind, key), *args, **kwargs)
framework._emit(event)
[docs]class HandleKind:
"""Helper descriptor to define the Object.handle_kind field.
The handle_kind for an object defaults to its type name, but it may
be explicitly overridden if desired.
"""
def __get__(self, obj, obj_type):
kind = obj_type.__dict__.get("handle_kind")
if kind:
return kind
return obj_type.__name__
class _Metaclass(type):
"""Helper class to ensure proper instantiation of Object-derived classes.
This class currently has a single purpose: events derived from EventSource
that are class attributes of Object-derived classes need to be told what
their name is in that class. For example, in
class SomeObject(Object):
something_happened = EventSource(SomethingHappened)
the instance of EventSource needs to know it's called 'something_happened'.
Starting from python 3.6 we could use __set_name__ on EventSource for this,
but until then this (meta)class does the equivalent work.
TODO: when we drop support for 3.5 drop this class, and rename _set_name in
EventSource to __set_name__; everything should continue to work.
"""
def __new__(typ, *a, **kw):
k = super().__new__(typ, *a, **kw)
# k is now the Object-derived class; loop over its class attributes
for n, v in vars(k).items():
# we could do duck typing here if we want to support
# non-EventSource-derived shenanigans. We don't.
if isinstance(v, EventSource):
# this is what 3.6+ does automatically for us:
v._set_name(k, n)
return k
[docs]class Object(metaclass=_Metaclass):
"""Base class of all the charm-related objects."""
handle_kind = HandleKind()
def __init__(self, parent, key):
kind = self.handle_kind
if isinstance(parent, Framework):
self.framework = parent
# Avoid Framework instances having a circular reference to themselves.
if self.framework is self:
self.framework = weakref.proxy(self.framework)
self.handle = Handle(None, kind, key)
else:
self.framework = parent.framework
self.handle = Handle(parent, kind, key)
self.framework._track(self)
# TODO Detect conflicting handles here.
@property
def model(self):
"""Shortcut for more simple access the model."""
return self.framework.model
[docs]class ObjectEvents(Object):
"""Convenience type to allow defining .on attributes at class level."""
handle_kind = "on"
def __init__(self, parent=None, key=None):
if parent is not None:
super().__init__(parent, key)
else:
self._cache = weakref.WeakKeyDictionary()
def __get__(self, emitter, emitter_type):
if emitter is None:
return self
instance = self._cache.get(emitter)
if instance is None:
# Same type, different instance, more data. Doing this unusual construct
# means people can subclass just this one class to have their own 'on'.
instance = self._cache[emitter] = type(self)(emitter)
return instance
[docs] @classmethod
def define_event(cls, event_kind, event_type):
"""Define an event on this type at runtime.
cls: a type to define an event on.
event_kind: an attribute name that will be used to access the
event. Must be a valid python identifier, not be a keyword
or an existing attribute.
event_type: a type of the event to define.
"""
prefix = 'unable to define an event with event_kind that '
if not event_kind.isidentifier():
raise RuntimeError(prefix + 'is not a valid python identifier: ' + event_kind)
elif keyword.iskeyword(event_kind):
raise RuntimeError(prefix + 'is a python keyword: ' + event_kind)
try:
getattr(cls, event_kind)
raise RuntimeError(
prefix + 'overlaps with an existing type {} attribute: {}'.format(cls, event_kind))
except AttributeError:
pass
event_descriptor = EventSource(event_type)
event_descriptor._set_name(cls, event_kind)
setattr(cls, event_kind, event_descriptor)
def _event_kinds(self):
event_kinds = []
# We have to iterate over the class rather than instance to allow for properties which
# might call this method (e.g., event views), leading to infinite recursion.
for attr_name, attr_value in inspect.getmembers(type(self)):
if isinstance(attr_value, EventSource):
# We actually care about the bound_event, however, since it
# provides the most info for users of this method.
event_kinds.append(attr_name)
return event_kinds
[docs] def events(self):
"""Return a mapping of event_kinds to bound_events for all available events."""
return {event_kind: getattr(self, event_kind) for event_kind in self._event_kinds()}
def __getitem__(self, key):
return PrefixedEvents(self, key)
def __repr__(self):
k = type(self)
event_kinds = ', '.join(sorted(self._event_kinds()))
return '<{}.{}: {}>'.format(k.__module__, k.__qualname__, event_kinds)
[docs]class PrefixedEvents:
"""Events to be found in all events using a specific prefix."""
def __init__(self, emitter, key):
self._emitter = emitter
self._prefix = key.replace("-", "_") + '_'
def __getattr__(self, name):
return getattr(self._emitter, self._prefix + name)
[docs]class PreCommitEvent(EventBase):
"""Events that will be emited first on commit."""
[docs]class CommitEvent(EventBase):
"""Events that will be emited second on commit."""
[docs]class FrameworkEvents(ObjectEvents):
"""Manager of all framework events."""
pre_commit = EventSource(PreCommitEvent)
commit = EventSource(CommitEvent)
[docs]class NoTypeError(Exception):
"""No class to hold it was found when restoring an event."""
def __init__(self, handle_path):
self.handle_path = handle_path
def __str__(self):
return "cannot restore {} since no class was registered for it".format(self.handle_path)
# the message to show to the user when a pdb breakpoint goes active
_BREAKPOINT_WELCOME_MESSAGE = """
Starting pdb to debug charm operator.
Run `h` for help, `c` to continue, or `exit`/CTRL-d to abort.
Future breakpoints may interrupt execution again.
More details at https://discourse.jujucharms.com/t/debugging-charm-hooks
"""
_event_regex = r'^(|.*/)on/[a-zA-Z_]+\[\d+\]$'
[docs]class Framework(Object):
"""Main interface to from the Charm to the Operator Framework internals."""
on = FrameworkEvents()
# Override properties from Object so that we can set them in __init__.
model = None
meta = None
charm_dir = None
def __init__(self, storage, charm_dir, meta, model):
super().__init__(self, None)
self.charm_dir = charm_dir
self.meta = meta
self.model = model
self._observers = [] # [(observer_path, method_name, parent_path, event_key)]
self._observer = weakref.WeakValueDictionary() # {observer_path: observer}
self._objects = weakref.WeakValueDictionary()
self._type_registry = {} # {(parent_path, kind): cls}
self._type_known = set() # {cls}
if isinstance(storage, (str, pathlib.Path)):
logger.warning(
"deprecated: Framework now takes a Storage not a path")
storage = SQLiteStorage(storage)
self._storage = storage
# We can't use the higher-level StoredState because it relies on events.
self.register_type(StoredStateData, None, StoredStateData.handle_kind)
stored_handle = Handle(None, StoredStateData.handle_kind, '_stored')
try:
self._stored = self.load_snapshot(stored_handle)
except NoSnapshotError:
self._stored = StoredStateData(self, '_stored')
self._stored['event_count'] = 0
# Flag to indicate that we already presented the welcome message in a debugger breakpoint
self._breakpoint_welcomed = False
# Parse the env var once, which may be used multiple times later
debug_at = os.environ.get('JUJU_DEBUG_AT')
self._juju_debug_at = debug_at.split(',') if debug_at else ()
[docs] def set_breakpointhook(self):
"""Hook into sys.breakpointhook so the builtin breakpoint() works as expected.
This method is called by ``main``, and is not intended to be
called by users of the framework itself outside of perhaps
some testing scenarios.
It returns the old value of sys.excepthook.
The breakpoint function is a Python >= 3.7 feature.
This method was added in ops 1.0; before that, it was done as
part of the Framework's __init__.
"""
old_breakpointhook = getattr(sys, 'breakpointhook', None)
if old_breakpointhook is not None:
# Hook into builtin breakpoint, so if Python >= 3.7, devs will be able to just do
# breakpoint()
sys.breakpointhook = self.breakpoint
return old_breakpointhook
[docs] def close(self):
"""Close the underlying backends."""
self._storage.close()
def _track(self, obj):
"""Track object and ensure it is the only object created using its handle path."""
if obj is self:
# Framework objects don't track themselves
return
if obj.handle.path in self.framework._objects:
raise RuntimeError(
'two objects claiming to be {} have been created'.format(obj.handle.path))
self._objects[obj.handle.path] = obj
def _forget(self, obj):
"""Stop tracking the given object. See also _track."""
self._objects.pop(obj.handle.path, None)
[docs] def commit(self):
"""Save changes to the underlying backends."""
# Give a chance for objects to persist data they want to before a commit is made.
self.on.pre_commit.emit()
# Make sure snapshots are saved by instances of StoredStateData. Any possible state
# modifications in on_commit handlers of instances of other classes will not be persisted.
self.on.commit.emit()
# Save our event count after all events have been emitted.
self.save_snapshot(self._stored)
self._storage.commit()
[docs] def register_type(self, cls, parent, kind=None):
"""Register a type to a handle."""
if parent and not isinstance(parent, Handle):
parent = parent.handle
if parent:
parent_path = parent.path
else:
parent_path = None
if not kind:
kind = cls.handle_kind
self._type_registry[(parent_path, kind)] = cls
self._type_known.add(cls)
[docs] def save_snapshot(self, value):
"""Save a persistent snapshot of the provided value.
The provided value must implement the following interface:
value.handle = Handle(...)
value.snapshot() => {...} # Simple builtin types only.
value.restore(snapshot) # Restore custom state from prior snapshot.
"""
if type(value) not in self._type_known:
raise RuntimeError(
'cannot save {} values before registering that type'.format(type(value).__name__))
data = value.snapshot()
# Use marshal as a validator, enforcing the use of simple types, as we later the
# information is really pickled, which is too error prone for future evolution of the
# stored data (e.g. if the developer stores a custom object and later changes its
# class name; when unpickling the original class will not be there and event
# data loading will fail).
try:
marshal.dumps(data)
except ValueError:
msg = "unable to save the data for {}, it must contain only simple types: {!r}"
raise ValueError(msg.format(value.__class__.__name__, data))
self._storage.save_snapshot(value.handle.path, data)
[docs] def load_snapshot(self, handle):
"""Load a persistent snapshot."""
parent_path = None
if handle.parent:
parent_path = handle.parent.path
cls = self._type_registry.get((parent_path, handle.kind))
if not cls:
raise NoTypeError(handle.path)
data = self._storage.load_snapshot(handle.path)
obj = cls.__new__(cls)
obj.framework = self
obj.handle = handle
obj.restore(data)
self._track(obj)
return obj
[docs] def drop_snapshot(self, handle):
"""Discard a persistent snapshot."""
self._storage.drop_snapshot(handle.path)
[docs] def observe(self, bound_event: BoundEvent, observer: types.MethodType):
"""Register observer to be called when bound_event is emitted.
The bound_event is generally provided as an attribute of the object that emits
the event, and is created in this style::
class SomeObject:
something_happened = Event(SomethingHappened)
That event may be observed as::
framework.observe(someobj.something_happened, self._on_something_happened)
Raises:
RuntimeError: if bound_event or observer are the wrong type.
"""
if not isinstance(bound_event, BoundEvent):
raise RuntimeError(
'Framework.observe requires a BoundEvent as second parameter, got {}'.format(
bound_event))
if not isinstance(observer, types.MethodType):
# help users of older versions of the framework
if isinstance(observer, charm.CharmBase):
raise TypeError(
'observer methods must now be explicitly provided;'
' please replace observe(self.on.{0}, self)'
' with e.g. observe(self.on.{0}, self._on_{0})'.format(
bound_event.event_kind))
raise RuntimeError(
'Framework.observe requires a method as third parameter, got {}'.format(observer))
event_type = bound_event.event_type
event_kind = bound_event.event_kind
emitter = bound_event.emitter
self.register_type(event_type, emitter, event_kind)
if hasattr(emitter, "handle"):
emitter_path = emitter.handle.path
else:
raise RuntimeError(
'event emitter {} must have a "handle" attribute'.format(type(emitter).__name__))
# Validate that the method has an acceptable call signature.
sig = inspect.signature(observer)
# Self isn't included in the params list, so the first arg will be the event.
extra_params = list(sig.parameters.values())[1:]
method_name = observer.__name__
observer = observer.__self__
if not sig.parameters:
raise TypeError(
'{}.{} must accept event parameter'.format(type(observer).__name__, method_name))
elif any(param.default is inspect.Parameter.empty for param in extra_params):
# Allow for additional optional params, since there's no reason to exclude them, but
# required params will break.
raise TypeError(
'{}.{} has extra required parameter'.format(type(observer).__name__, method_name))
# TODO Prevent the exact same parameters from being registered more than once.
self._observer[observer.handle.path] = observer
self._observers.append((observer.handle.path, method_name, emitter_path, event_kind))
def _next_event_key(self):
"""Return the next event key that should be used, incrementing the internal counter."""
# Increment the count first; this means the keys will start at 1, and 0
# means no events have been emitted.
self._stored['event_count'] += 1
return str(self._stored['event_count'])
def _emit(self, event):
"""See BoundEvent.emit for the public way to call this."""
saved = False
event_path = event.handle.path
event_kind = event.handle.kind
parent_path = event.handle.parent.path
# TODO Track observers by (parent_path, event_kind) rather than as a list of
# all observers. Avoiding linear search through all observers for every event
for observer_path, method_name, _parent_path, _event_kind in self._observers:
if _parent_path != parent_path:
continue
if _event_kind and _event_kind != event_kind:
continue
if not saved:
# Save the event for all known observers before the first notification
# takes place, so that either everyone interested sees it, or nobody does.
self.save_snapshot(event)
saved = True
# Again, only commit this after all notices are saved.
self._storage.save_notice(event_path, observer_path, method_name)
if saved:
self._reemit(event_path)
[docs] def reemit(self):
"""Reemit previously deferred events to the observers that deferred them.
Only the specific observers that have previously deferred the event will be
notified again. Observers that asked to be notified about events after it's
been first emitted won't be notified, as that would mean potentially observing
events out of order.
"""
self._reemit()
def _reemit(self, single_event_path=None):
last_event_path = None
deferred = True
for event_path, observer_path, method_name in self._storage.notices(single_event_path):
event_handle = Handle.from_path(event_path)
if last_event_path != event_path:
if not deferred and last_event_path is not None:
self._storage.drop_snapshot(last_event_path)
last_event_path = event_path
deferred = False
try:
event = self.load_snapshot(event_handle)
except NoTypeError:
self._storage.drop_notice(event_path, observer_path, method_name)
continue
event.deferred = False
observer = self._observer.get(observer_path)
if observer:
if single_event_path is None:
logger.debug("Re-emitting %s.", event)
custom_handler = getattr(observer, method_name, None)
if custom_handler:
event_is_from_juju = isinstance(event, charm.HookEvent)
event_is_action = isinstance(event, charm.ActionEvent)
if (event_is_from_juju or event_is_action) and 'hook' in self._juju_debug_at:
# Present the welcome message and run under PDB.
self._show_debug_code_message()
pdb.runcall(custom_handler, event)
else:
# Regular call to the registered method.
custom_handler(event)
if event.deferred:
deferred = True
else:
self._storage.drop_notice(event_path, observer_path, method_name)
# We intentionally consider this event to be dead and reload it from
# scratch in the next path.
self.framework._forget(event)
if not deferred and last_event_path is not None:
self._storage.drop_snapshot(last_event_path)
def _show_debug_code_message(self):
"""Present the welcome message (only once!) when using debugger functionality."""
if not self._breakpoint_welcomed:
self._breakpoint_welcomed = True
print(_BREAKPOINT_WELCOME_MESSAGE, file=sys.stderr, end='')
[docs] def breakpoint(self, name=None):
"""Add breakpoint, optionally named, at the place where this method is called.
For the breakpoint to be activated the JUJU_DEBUG_AT environment variable
must be set to "all" or to the specific name parameter provided, if any. In every
other situation calling this method does nothing.
The framework also provides a standard breakpoint named "hook", that will
stop execution when a hook event is about to be handled.
For those reasons, the "all" and "hook" breakpoint names are reserved.
"""
# If given, validate the name comply with all the rules
if name is not None:
if not isinstance(name, str):
raise TypeError('breakpoint names must be strings')
if name in ('hook', 'all'):
raise ValueError('breakpoint names "all" and "hook" are reserved')
if not re.match(r'^[a-z0-9]([a-z0-9\-]*[a-z0-9])?$', name):
raise ValueError('breakpoint names must look like "foo" or "foo-bar"')
indicated_breakpoints = self._juju_debug_at
if not indicated_breakpoints:
return
if 'all' in indicated_breakpoints or name in indicated_breakpoints:
self._show_debug_code_message()
# If we call set_trace() directly it will open the debugger *here*, so indicating
# it to use our caller's frame
code_frame = inspect.currentframe().f_back
pdb.Pdb().set_trace(code_frame)
else:
logger.warning(
"Breakpoint %r skipped (not found in the requested breakpoints: %s)",
name, indicated_breakpoints)
[docs] def remove_unreferenced_events(self):
"""Remove events from storage that are not referenced.
In older versions of the framework, events that had no observers would get recorded but
never deleted. This makes a best effort to find these events and remove them from the
database.
"""
event_regex = re.compile(_event_regex)
to_remove = []
for handle_path in self._storage.list_snapshots():
if event_regex.match(handle_path):
notices = self._storage.notices(handle_path)
if next(notices, None) is None:
# There are no notices for this handle_path, it is valid to remove it
to_remove.append(handle_path)
for handle_path in to_remove:
self._storage.drop_snapshot(handle_path)
[docs]class StoredStateData(Object):
"""Manager of the stored data."""
def __init__(self, parent, attr_name):
super().__init__(parent, attr_name)
self._cache = {}
self.dirty = False
def __getitem__(self, key):
return self._cache.get(key)
def __setitem__(self, key, value):
self._cache[key] = value
self.dirty = True
def __contains__(self, key):
return key in self._cache
[docs] def snapshot(self):
"""Return the current state."""
return self._cache
[docs] def restore(self, snapshot):
"""Restore current state to the given snapshot."""
self._cache = snapshot
self.dirty = False
[docs] def on_commit(self, event):
"""Save changes to the storage backend."""
if self.dirty:
self.framework.save_snapshot(self)
self.dirty = False
[docs]class BoundStoredState:
"""Stored state data bound to a specific Object."""
def __init__(self, parent, attr_name):
parent.framework.register_type(StoredStateData, parent)
handle = Handle(parent, StoredStateData.handle_kind, attr_name)
try:
data = parent.framework.load_snapshot(handle)
except NoSnapshotError:
data = StoredStateData(parent, attr_name)
# __dict__ is used to avoid infinite recursion.
self.__dict__["_data"] = data
self.__dict__["_attr_name"] = attr_name
parent.framework.observe(parent.framework.on.commit, self._data.on_commit)
def __getattr__(self, key):
# "on" is the only reserved key that can't be used in the data map.
if key == "on":
return self._data.on
if key not in self._data:
raise AttributeError("attribute '{}' is not stored".format(key))
return _wrap_stored(self._data, self._data[key])
def __setattr__(self, key, value):
if key == "on":
raise AttributeError("attribute 'on' is reserved and cannot be set")
value = _unwrap_stored(self._data, value)
if not isinstance(value, (type(None), int, float, str, bytes, list, dict, set)):
raise AttributeError(
'attribute {!r} cannot be a {}: must be int/float/dict/list/etc'.format(
key, type(value).__name__))
self._data[key] = _unwrap_stored(self._data, value)
[docs] def set_default(self, **kwargs):
"""Set the value of any given key if it has not already been set."""
for k, v in kwargs.items():
if k not in self._data:
self._data[k] = v
[docs]class StoredState:
"""A class used to store data the charm needs persisted across invocations.
Example::
class MyClass(Object):
_stored = StoredState()
Instances of `MyClass` can transparently save state between invocations by
setting attributes on `_stored`. Initial state should be set with
`set_default` on the bound object, that is::
class MyClass(Object):
_stored = StoredState()
def __init__(self, parent, key):
super().__init__(parent, key)
self._stored.set_default(seen=set())
self.framework.observe(self.on.seen, self._on_seen)
def _on_seen(self, event):
self._stored.seen.add(event.uuid)
"""
def __init__(self):
self.parent_type = None
self.attr_name = None
def __get__(self, parent, parent_type=None):
if self.parent_type is not None and self.parent_type not in parent_type.mro():
# the StoredState instance is being shared between two unrelated classes
# -> unclear what is exepcted of us -> bail out
raise RuntimeError(
'StoredState shared by {} and {}'.format(
self.parent_type.__name__, parent_type.__name__))
if parent is None:
# accessing via the class directly (e.g. MyClass.stored)
return self
bound = None
if self.attr_name is not None:
bound = parent.__dict__.get(self.attr_name)
if bound is not None:
# we already have the thing from a previous pass, huzzah
return bound
# need to find ourselves amongst the parent's bases
for cls in parent_type.mro():
for attr_name, attr_value in cls.__dict__.items():
if attr_value is not self:
continue
# we've found ourselves! is it the first time?
if bound is not None:
# the StoredState instance is being stored in two different
# attributes -> unclear what is expected of us -> bail out
raise RuntimeError("StoredState shared by {0}.{1} and {0}.{2}".format(
cls.__name__, self.attr_name, attr_name))
# we've found ourselves for the first time; save where, and bind the object
self.attr_name = attr_name
self.parent_type = cls
bound = BoundStoredState(parent, attr_name)
if bound is not None:
# cache the bound object to avoid the expensive lookup the next time
# (don't use setattr, to keep things symmetric with the fast-path lookup above)
parent.__dict__[self.attr_name] = bound
return bound
raise AttributeError(
'cannot find {} attribute in type {}'.format(
self.__class__.__name__, parent_type.__name__))
def _wrap_stored(parent_data, value):
t = type(value)
if t is dict:
return StoredDict(parent_data, value)
if t is list:
return StoredList(parent_data, value)
if t is set:
return StoredSet(parent_data, value)
return value
def _unwrap_stored(parent_data, value):
t = type(value)
if t is StoredDict or t is StoredList or t is StoredSet:
return value._under
return value
def _wrapped_repr(obj):
t = type(obj)
if obj._under:
return "{}.{}({!r})".format(t.__module__, t.__name__, obj._under)
else:
return "{}.{}()".format(t.__module__, t.__name__)
[docs]class StoredDict(collections.abc.MutableMapping):
"""A dict-like object that uses the StoredState as backend."""
def __init__(self, stored_data, under):
self._stored_data = stored_data
self._under = under
def __getitem__(self, key):
return _wrap_stored(self._stored_data, self._under[key])
def __setitem__(self, key, value):
self._under[key] = _unwrap_stored(self._stored_data, value)
self._stored_data.dirty = True
def __delitem__(self, key):
del self._under[key]
self._stored_data.dirty = True
def __iter__(self):
return self._under.__iter__()
def __len__(self):
return len(self._under)
def __eq__(self, other):
if isinstance(other, StoredDict):
return self._under == other._under
elif isinstance(other, collections.abc.Mapping):
return self._under == other
else:
return NotImplemented
__repr__ = _wrapped_repr
[docs]class StoredList(collections.abc.MutableSequence):
"""A list-like object that uses the StoredState as backend."""
def __init__(self, stored_data, under):
self._stored_data = stored_data
self._under = under
def __getitem__(self, index):
return _wrap_stored(self._stored_data, self._under[index])
def __setitem__(self, index, value):
self._under[index] = _unwrap_stored(self._stored_data, value)
self._stored_data.dirty = True
def __delitem__(self, index):
del self._under[index]
self._stored_data.dirty = True
def __len__(self):
return len(self._under)
[docs] def insert(self, index, value):
"""Insert value before index."""
self._under.insert(index, value)
self._stored_data.dirty = True
[docs] def append(self, value):
"""Append value to the end of the list."""
self._under.append(value)
self._stored_data.dirty = True
def __eq__(self, other):
if isinstance(other, StoredList):
return self._under == other._under
elif isinstance(other, collections.abc.Sequence):
return self._under == other
else:
return NotImplemented
def __lt__(self, other):
if isinstance(other, StoredList):
return self._under < other._under
elif isinstance(other, collections.abc.Sequence):
return self._under < other
else:
return NotImplemented
def __le__(self, other):
if isinstance(other, StoredList):
return self._under <= other._under
elif isinstance(other, collections.abc.Sequence):
return self._under <= other
else:
return NotImplemented
def __gt__(self, other):
if isinstance(other, StoredList):
return self._under > other._under
elif isinstance(other, collections.abc.Sequence):
return self._under > other
else:
return NotImplemented
def __ge__(self, other):
if isinstance(other, StoredList):
return self._under >= other._under
elif isinstance(other, collections.abc.Sequence):
return self._under >= other
else:
return NotImplemented
__repr__ = _wrapped_repr
[docs]class StoredSet(collections.abc.MutableSet):
"""A set-like object that uses the StoredState as backend."""
def __init__(self, stored_data, under):
self._stored_data = stored_data
self._under = under
[docs] def add(self, key):
"""Add a key to a set.
This has no effect if the key is already present.
"""
self._under.add(key)
self._stored_data.dirty = True
[docs] def discard(self, key):
"""Remove a key from a set if it is a member.
If the key is not a member, do nothing.
"""
self._under.discard(key)
self._stored_data.dirty = True
def __contains__(self, key):
return key in self._under
def __iter__(self):
return self._under.__iter__()
def __len__(self):
return len(self._under)
@classmethod
def _from_iterable(cls, it):
"""Construct an instance of the class from any iterable input.
Per https://docs.python.org/3/library/collections.abc.html
if the Set mixin is being used in a class with a different constructor signature,
you will need to override _from_iterable() with a classmethod that can construct
new instances from an iterable argument.
"""
return set(it)
def __le__(self, other):
if isinstance(other, StoredSet):
return self._under <= other._under
elif isinstance(other, collections.abc.Set):
return self._under <= other
else:
return NotImplemented
def __ge__(self, other):
if isinstance(other, StoredSet):
return self._under >= other._under
elif isinstance(other, collections.abc.Set):
return self._under >= other
else:
return NotImplemented
def __eq__(self, other):
if isinstance(other, StoredSet):
return self._under == other._under
elif isinstance(other, collections.abc.Set):
return self._under == other
else:
return NotImplemented
__repr__ = _wrapped_repr