diff options
| -rw-r--r-- | src/rabbit_backing_queue.erl | 38 |
1 files changed, 31 insertions, 7 deletions
diff --git a/src/rabbit_backing_queue.erl b/src/rabbit_backing_queue.erl index a15ff846f6..fe09e40042 100644 --- a/src/rabbit_backing_queue.erl +++ b/src/rabbit_backing_queue.erl @@ -39,13 +39,12 @@ behaviour_info(callbacks) -> %% 2. a boolean indicating whether the queue is durable %% 3. a boolean indicating whether the queue is an existing queue %% that should be recovered - %% 4. an asynchronous callback which accepts a function from - %% state to state and invokes it with the current backing - %% queue state. This is useful for handling events, e.g. when - %% the backing queue does not have its own process to receive - %% such events, or when the processing of an event results in - %% a state transition the queue logic needs to know about - %% (such as messages getting confirmed). + %% 4. 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. %% 5. a synchronous callback. Same as the asynchronous callback %% but waits for completion and returns 'error' on error. {init, 5}, @@ -71,6 +70,31 @@ behaviour_info(callbacks) -> %% 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 the 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 |