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core.messaging.dispatchers.message_dispatcher

MessageDispatcher Objects​

class MessageDispatcher(abc.ABC, typing.Generic[MessageType])

Base message dispatcher responsible for sending messages to registered handlers.

Dispatching a message (locally) is done by passing the message to one or more registered message handlers within a Service. The message dispatcher also performs pre- and post-dispatching tasks and takes care of catching errors raised in a handler.

__init__​

def __init__(meta_information_type: type[MessageMetaInformationType])

Arguments:

  • meta_information_type - The required type of the message meta information passed alongside the actual messages.

process​

def process() -> None

Called to perform periodic tasks.

pre_dispatch​

def pre_dispatch(msg: MessageType,
                 msg_meta: MessageMetaInformationType) -> None

Called to perform tasks before sending a message.

This method is called before any service-registered message handler is invoked.

Arguments:

  • msg - The message that is about to be dispatched.
  • msg_meta - The message meta information.

Raises:

  • RuntimeError - If the meta information type is invalid.

dispatch​

def dispatch(msg: MessageType, msg_meta: MessageMetaInformationType,
             handler: MessageHandlerMapping, ctx: MessageContextType) -> None

Dispatches a message to locally registered message handlers.

Handlers can be either called synchronously or asynchronously, depending on how the handler was registered.

Notes:

Exceptions arising within a message handler will not interrupt the running program; instead, such errors will only be logged.

Arguments:

  • msg - The message to be dispatched.
  • msg_meta - The message meta information.
  • handler - The handler to be invoked.
  • ctx - The message context.

Raises:

  • RuntimeError - If the handler requires a different message type.

post_dispatch​

def post_dispatch(msg: MessageType,
                  msg_meta: MessageMetaInformationType) -> None

Called to perform tasks after sending a message.

This method is called after any service-registered message handler have been invoked.

Arguments:

  • msg - The message that has just been dispatched.
  • msg_meta - The message meta information.