Spring Itegration Aggregator: meaning of “send-timeout” XML configuration

Question

I would appreciate some clarification about the meaning of "send-timeout" configuration parameter for an Aggregator. Based on Spring documentation, this configuration is The timeout interval for sending the aggregated messages to the output or reply channel. Optional.

Now, based on my understanding the Aggregator is a passive component and only decides to send a message or not based on the result of the release strategy after the receipt of a message; it won't release messages based on timeout events, for that, a separate Reaper component is needed. Is this correct?

Assuming, the send-timeout is the maximum amount of time that the Aggregator can spend sending the completed group of messages to the output channel. What would happen if time runs out (due to this parameter set up) while sending a message. How will the Aggregator handle that message group that was ready to release, started to be sent but never finished? Will it be marked complete?

Thanks

Answer 1

This is a fairly commonly misunderstood attribute. In many places (but not all) we have explained it clearly in the XSD and docs.

Bottom line is it rarely is applied. It only applies when the output channel can block. For example, if the output-channel is a QueueChannel with a capacity and the queue is full; it is the time we will wait to send the message to the channel.

If the output channel is, for example, a DirectChannel, it never applies.

If it does apply, the exception will be thrown back to the caller and the group will remain. Attempts to re-release such groups will occur if you configure a MessageGroupStoreReaper; if the group is still eligible for release, the reaper will again attempt to send the group to the output channel.

The "stuck" group will also be released if new messages arrives for the same group and the release strategy still considers the group eligible (e.g. it uses size >= n rather than size == n).

BTW, while the aggregator is generally a passive component, we did introduce the group-timeout (and group-timeout-expression) in 4.0 which allows partial groups to be released after a timeout, even without a reaper.

However, if such a release fails to happen because of the send-timeout, a new release attempt will only be made if a reaper is configured.