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|
%% The contents of this file are subject to the Mozilla Public License
%% Version 1.1 (the "License"); you may not use this file except in
%% compliance with the License. You may obtain a copy of the License
%% at http://www.mozilla.org/MPL/
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and
%% limitations under the License.
%%
%% The Original Code is RabbitMQ.
%%
%% The Initial Developer of the Original Code is VMware, Inc.
%% Copyright (c) 2007-2012 VMware, Inc. All rights reserved.
%%
-module(rabbit_backing_queue).
-export([behaviour_info/1]).
behaviour_info(callbacks) ->
[
%% Called on startup with a list of durable queue names. The
%% queues aren't being started at this point, but this call
%% allows the backing queue to perform any checking necessary for
%% the consistency of those queues, or initialise any other
%% shared resources.
{start, 1},
%% Called to tear down any state/resources. NB: Implementations
%% should not depend on this function being called on shutdown
%% and instead should hook into the rabbit supervision hierarchy.
{stop, 0},
%% Initialise the backing queue and its state.
%%
%% Takes
%% 1. the amqqueue record
%% 2. a boolean indicating whether the queue is an existing queue
%% that should be recovered
%% 3. an asynchronous callback which accepts a function of type
%% backing-queue-state to backing-queue-state. This callback
%% function can be safely invoked from any process, which
%% makes it useful for passing messages back into the backing
%% queue, especially as the backing queue does not have
%% control of its own mailbox.
{init, 3},
%% Called on queue shutdown when queue isn't being deleted.
{terminate, 2},
%% Called when the queue is terminating and needs to delete all
%% its content.
{delete_and_terminate, 2},
%% Remove all messages in the queue, but not messages which have
%% been fetched and are pending acks.
{purge, 1},
%% Publish a message.
{publish, 4},
%% Called for messages which have already been passed straight
%% out to a client. The queue will be empty for these calls
%% (i.e. saves the round trip through the backing queue).
{publish_delivered, 5},
%% Return ids of messages which have been confirmed since
%% the last invocation of this function (or initialisation).
%%
%% Message ids should only appear in the result of
%% drain_confirmed under the following circumstances:
%%
%% 1. The message appears in a call to publish_delivered/4 and
%% the first argument (ack_required) is false; or
%% 2. The message is fetched from the queue with fetch/2 and the
%% first argument (ack_required) is false; or
%% 3. The message is acked (ack/2 is called for the message); or
%% 4. The message is fully fsync'd to disk in such a way that the
%% recovery of the message is guaranteed in the event of a
%% crash of this rabbit node (excluding hardware failure).
%%
%% In addition to the above conditions, a message id may only
%% appear in the result of drain_confirmed if
%% #message_properties.needs_confirming = true when the msg was
%% published (through whichever means) to the backing queue.
%%
%% It is legal for the same message id to appear in the results
%% of multiple calls to drain_confirmed, which means that the
%% backing queue is not required to keep track of which messages
%% it has already confirmed. The confirm will be issued to the
%% publisher the first time the message id appears in the result
%% of drain_confirmed. All subsequent appearances of that message
%% id will be ignored.
{drain_confirmed, 1},
%% Drop messages from the head of the queue while the supplied
%% predicate returns true. A callback function is supplied
%% allowing callers access to messages that are about to be
%% dropped.
{dropwhile, 3},
%% Produce the next message.
{fetch, 2},
%% Acktags supplied are for messages which can now be forgotten
%% about. Must return 1 msg_id per Ack, in the same order as
%% Acks.
{ack, 2},
%% Acktags supplied are for messages which should be
%% processed. The provided callback function is called with each
%% message.
{fold, 3},
%% Reinsert messages into the queue which have already been
%% delivered and were pending acknowledgement.
{requeue, 2},
%% How long is my queue?
{len, 1},
%% Is my queue empty?
{is_empty, 1},
%% For the next three functions, the assumption is that you're
%% monitoring something like the ingress and egress rates of the
%% queue. The RAM duration is thus the length of time represented
%% by the messages held in RAM given the current rates. If you
%% want to ignore all of this stuff, then do so, and return 0 in
%% ram_duration/1.
%% The target is to have no more messages in RAM than indicated
%% by the duration and the current queue rates.
{set_ram_duration_target, 2},
%% Optionally recalculate the duration internally (likely to be
%% just update your internal rates), and report how many seconds
%% the messages in RAM represent given the current rates of the
%% queue.
{ram_duration, 1},
%% Should 'timeout' be called as soon as the queue process
%% can manage (either on an empty mailbox, or when a timer
%% fires)?
{needs_timeout, 1},
%% Called (eventually) after needs_timeout returns 'idle' or
%% 'timed'. Note this may be called more than once for each
%% 'idle' or 'timed' returned from needs_timeout.
{timeout, 1},
%% Called immediately before the queue hibernates.
{handle_pre_hibernate, 1},
%% Exists for debugging purposes, to be able to expose state via
%% rabbitmqctl list_queues backing_queue_status
{status, 1},
%% Passed a function to be invoked with the relevant backing
%% queue's state. Useful for when the backing queue or other
%% components need to pass functions into the backing queue.
{invoke, 3},
%% Called prior to a publish or publish_delivered call. Allows
%% the BQ to signal that it's already seen this message (and in
%% what capacity - i.e. was it published previously or discarded
%% previously) and thus the message should be dropped.
{is_duplicate, 2},
%% Called to inform the BQ about messages which have reached the
%% queue, but are not going to be further passed to BQ for some
%% reason. Note that this is may be invoked for messages for
%% which BQ:is_duplicate/2 has already returned {'published' |
%% 'discarded', BQS}.
{discard, 3}
];
behaviour_info(_Other) ->
undefined.
|
