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Project Task Page: Axon Waking Producers Bugfix

Status: Running
Current Developers: MH
Current "inflight" dev location: /branches/private_MH_axon_outboxwakeups
Start Date: 20 October 2006
Expected End Date: 31 November 2006
End Date: ???
Date this page last updated: 23 February 2007
Estimated effort so far: 5 days


To get Axon to wake up producer components when a message they have sent out is consumed. This used to be a feature of axon, but was removed when Axon box delivery optimisations were implemented. This is therefore effectively a bugfix.

This allows producers to sleep if an inbox they are trying to send to becomes full (because it is size limited) and then be woken when it becomes non-full.

Needed by the Mobile reframer.



This section is largely about WHO has influenced this task to do WHAT, and where possible WHY. It is also about WHO to contact with regard to this task to influence what's going on.

Task Sponsor: MH, MS

Task Owner: MH

Developers involved: MH (development), MS (merge)

Users: MH, MS

Interested third parties: MH, MS, SJ (bbc internal)


Relevant Influencing factors:





CVS branch: private_MH_axon_threads

Mainline code: /Code/Python/Axon/Axon/

Mainline code: /Code/Python/Axon/Axon/Tests

Realistic possibilities arising as a result of activity on this task


Tasks that directly enable this task (dependencies)

Sub Tasks

Task Log


This bug-fix brings Axon up to equivalent, but not semantically identical, functionality to the original capabilities of Axon 1.0.

Changes to behaviour/semantics

The original semantics worked for a model where both inbox and outbox sizes could be limited, and a postman microprocess would transfer data along linkages from outboxes to inboxes. In that model:

However, the box delivery optimisations removed the concept of messages being left in an outbox and a postman to carry them. Instead they are immediately and directly put into the final destination inbox.

The differences can therefore be summarised as:

In practical terms, this means that from the perspective of a component developer, behaviour has changed in the following way:

It was not deemed practical to perfectly replicate the old behaviour (without reverting to a postman style model) because of the lack of a concept of messages waiting for dispatch in the outbox.

Performance issues

It could be argued that this strategy of waking all producers may cause a significant performance hit to some Axon based systems as all producers linked to a consumer will be woken every time the consumer collects from that inbox.

An alternative would be to only wake producers when the inbox transitions from being full to becoming not-full. Alternatively, producers could only be woken if they explicitly request it.

However these ideas constitue a more fundamental change in behaviour that component developers would have to take into account, rather than being a simple bug-fix.

-- Matt Hammond, 23 February 2007