[WIP] Added TTLCacheDatastore with potential PubSub

[vshekar]

Checklist

• Add a Changelog entry
• Add the ticket number which this PR closes to the comment section

[danielballan]

I see a potential race here. Consider using itertools.count with collections.defaultdict.

[danielballan]

Maybe reuse the CallbackHandler? It's defined under tiled.client.streams but could be moved to tiled.calback_handler for use by client- or server-side modules.

tiled/tiled/client/stream.py

Lines 120 to 220 in 9746553

	class CallbackRegistry(Generic[T]):
	"""
	Distribute updates to user-provided callback functions.
	Parameters
	----------
	executor : concurrent.futures.Executor
	Launches tasks asynchronously, in response to updates
	"""
	def __init__(self, executor: concurrent.futures.Executor):
	self._executor = executor
	self._callbacks: set[T] = set()
	@property
	def executor(self):
	return self._executor
	def process(self, update: T):
	"Fan an update out to all registered callbacks."
	for ref in self._callbacks:
	callback = ref()
	if callback is not None:
	self.executor.submit(callback, update)
	def add_callback(self, callback: Callback[T]) -> Self:
	"""
	Register a callback to be run when the Subscription receives an update.
	The callback registry only holds a weak reference to the callback. If
	no hard references are held elsewhere in the program, the callback will
	be silently removed.
	Parameters
	----------
	callback : Callback
	Returns
	-------
	Subscription
	Examples
	--------
	Simply subscribe the print function.
	>>> sub.add_callback(print)
	Subscribe a custom function.
	>>> def f(sub, data):
	...
	>>> sub.add_callback(f)
	Start receiving updates, beginning with the next one.
	>>> sub.start()
	Or start receiving updates beginning as far back as the server has
	available.
	>>> sub.start(0)
	Or start receiving updates beginning with a specific sequence number.
	>>> sub.start(3)
	The method calls can be chained like:
	>>> sub.add_callback(f).add_callback(g).start()
	"""
	def cleanup(ref: weakref.ref) -> None:
	# When an object is garbage collected, remove its entry
	# from the set of callbacks.
	self._callbacks.remove(ref)
	if inspect.ismethod(callback):
	# This holds the reference to the method until the object it is
	# bound to is garbage collected.
	ref = weakref.WeakMethod(callback, cleanup)
	else:
	ref = weakref.ref(callback, cleanup)
	self._callbacks.add(ref)
	def remove_callback(self, callback: Callback[T]) -> Self:
	"""
	Unregister a callback.
	Parameters
	----------
	callback : Callback
	Returns
	-------
	Subscription
	"""
	self._callbacks.remove(callback)

[danielballan]

I'm not 100% sure this is a good idea. It's nice that your version is async. (This one uses threads.) Maybe just borrowing patterns from this rather than copy/pasting it would be better.