import typing
from hazelcast.future import Future
from hazelcast.protocol.codec import (
topic_add_message_listener_codec,
topic_publish_codec,
topic_remove_message_listener_codec,
)
from hazelcast.proxy.base import PartitionSpecificProxy, TopicMessage
from hazelcast.types import MessageType
from hazelcast.serialization.compact import SchemaNotReplicatedError
[docs]class Topic(PartitionSpecificProxy["BlockingTopic"], typing.Generic[MessageType]):
"""Hazelcast provides distribution mechanism for publishing messages that
are delivered to multiple subscribers, which is also known as a
publish/subscribe (pub/sub) messaging model.
Publish and subscriptions are cluster-wide. When a member subscribes for
a topic, it is actually registering for messages published by any member
in the cluster, including the new members joined after you added the
listener.
Messages are ordered, meaning that listeners(subscribers) will process the
messages in the order they are actually published.
"""
[docs] def add_listener(
self, on_message: typing.Callable[[TopicMessage[MessageType]], None] = None
) -> Future[str]:
"""Subscribes to this topic.
When someone publishes a message on this topic, ``on_message`` function
is called if provided.
Args:
on_message: Function to be called when a message is published.
Returns:
A registration id which is used as a key to remove the listener.
"""
codec = topic_add_message_listener_codec
request = codec.encode_request(self.name, self._is_smart)
def handle(item_data, publish_time, uuid):
member = self._context.cluster_service.get_member(uuid)
item_event = TopicMessage(
self.name, self._to_object(item_data), publish_time / 1000.0, member
)
on_message(item_event)
return self._register_listener(
request,
lambda r: codec.decode_response(r),
lambda reg_id: topic_remove_message_listener_codec.encode_request(self.name, reg_id),
lambda m: codec.handle(m, handle),
)
[docs] def publish(self, message: MessageType) -> Future[None]:
"""Publishes the message to all subscribers of this topic
Args:
message: The message to be published.
"""
try:
message_data = self._to_data(message)
except SchemaNotReplicatedError as e:
return self._send_schema_and_retry(e, self.publish, message)
request = topic_publish_codec.encode_request(self.name, message_data)
return self._invoke(request)
[docs] def remove_listener(self, registration_id: str) -> Future[bool]:
"""Stops receiving messages for the given message listener.
If the given listener already removed, this method does nothing.
Args:
registration_id: Registration id of the listener to be removed.
Returns:
``True`` if the listener is removed, ``False`` otherwise.
"""
return self._deregister_listener(registration_id)
[docs] def blocking(self) -> "BlockingTopic[MessageType]":
return BlockingTopic(self)
[docs]class BlockingTopic(Topic[MessageType]):
__slots__ = ("_wrapped", "name", "service_name")
def __init__(self, wrapped: Topic[MessageType]):
self.name = wrapped.name
self.service_name = wrapped.service_name
self._wrapped = wrapped
[docs] def add_listener( # type: ignore[override]
self,
on_message: typing.Callable[[TopicMessage[MessageType]], None] = None,
) -> str:
return self._wrapped.add_listener(on_message).result()
[docs] def publish( # type: ignore[override]
self,
message: MessageType,
) -> None:
return self._wrapped.publish(message).result()
[docs] def remove_listener( # type: ignore[override]
self,
registration_id: str,
) -> bool:
return self._wrapped.remove_listener(registration_id).result()
[docs] def destroy(self) -> bool:
return self._wrapped.destroy()
[docs] def blocking(self) -> "BlockingTopic[MessageType]":
return self
def __repr__(self) -> str:
return self._wrapped.__repr__()