从另一个线程获取消息的确认

pika/pika: Pure Python RabbitMQ/AMQP 0-9-1 client library
https://github.com/pika/pika#requesting-message-acknowledgements-from-another-thread

Requesting message acknowledgements from another thread

The single-threaded usage constraint of an individual Pika connection adapter instance may result in a dropped AMQP/stream connection due to AMQP heartbeat timeout in consumers that take a long time to process an incoming message. A common solution is to delegate processing of the incoming messages to another thread, while the connection adapter's thread continues to service its I/O loop's message pump, permitting AMQP heartbeats and other I/O to be serviced in a timely fashion.

Messages processed in another thread may not be acknowledged directly from that thread, since all accesses to the connection adapter instance must be from a single thread, which is the thread running the adapter's I/O loop. This is accomplished by requesting a callback to be executed in the adapter's I/O loop thread. For example, the callback function's implementation might look like this:

def ack_message(channel, delivery_tag):
    """Note that `channel` must be the same Pika channel instance via which
    the message being acknowledged was retrieved (AMQP protocol constraint).
    """
    if channel.is_open:
        channel.basic_ack(delivery_tag)
    else:
        # Channel is already closed, so we can't acknowledge this message;
        # log and/or do something that makes sense for your app in this case.
        pass

The code running in the other thread may request the ack_message() function to be executed in the connection adapter's I/O loop thread using an adapter-specific mechanism:

• pika.BlockingConnection abstracts its I/O loop from the application and thus exposes pika.BlockingConnection.add_callback_threadsafe(). Refer to this method's docstring for additional information. For example:

  connection.add_callback_threadsafe(functools.partial(ack_message, channel, delivery_tag))

• When using a non-blocking connection adapter, such as pika.adapters.asyncio_connection.AsyncioConnection orpika.SelectConnection, you use the underlying asynchronous framework's native API for requesting an I/O loop-bound callback from another thread. For example, pika.SelectConnection's I/O loop provides add_callback_threadsafe(),pika.adapters.tornado_connection.TornadoConnection's I/O loop has add_callback(), whilepika.adapters.asyncio_connection.AsyncioConnection's I/O loop exposes call_soon_threadsafe().

This threadsafe callback request mechanism may also be used to delegate publishing of messages, etc., from a background thread to the connection adapter's thread.