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 exposespika.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 providesadd_callback_threadsafe()
,pika.adapters.tornado_connection.TornadoConnection
's I/O loop hasadd_callback()
, whilepika.adapters.asyncio_connection.AsyncioConnection
's I/O loop exposescall_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.