Project Task Page: Axon ThreadedComponent API Change

Description

To change the design of ThreadedComponent so that when writing a component based on it, it is almost identical to writing a normal component (just leaving out the yield statements).

The existing design required the component writer to access queue objects to send and receive data, rather than use the self.dataReady(), self.send and self.recv() methods they would use for a normal component.

In the process, thread safety should also be improved, and the ability to add and remove inboxes and outboxes on the fly (ala AdaptiveCommsComponent) should be implemented.

Benefits:

• Much easier to write threaded components
• Very easy to convery a normal component to/from being a threaded one
  
• Possible to write threaded components that dynamically change their inboxes and outboxes (eg. Selector service component)
  

Inputs

• Task Sponsor: Michael (MS)
  
• Task Owner: Matt (MH)
  
• Developers involved: Matt (development), Michael (merging)
  
• Users: Matt, Michael
  
• Interested third parties: none
  
• Requirements
• Just like for a normal component, when writing a threaded one...
  
• MUST be able to use self.dataReady(), self.send() and self.recv()
  
• SHOULD be able to call the main body code main()
  
• MUST be thread safe for:
• sending messages
• receiving messages
• adding inboxes & outboxes
• removing inboxes & outboxes
• creating linkages
• destroying linkages
• SHOULD be able to trap exceptions and throw them back to the main thread so an Axon system can correctly terminate.
  

Relevant Influencing factors:

• Need to implement 'Selector' as a threaded component (for throughput optimisations)
  

Outputs

Expected

• Modifications to Axon (initially in branch, then merged into mainline code)
• Modifications and additions to Axon test suite

Actual

• Code:
• CVS branch: private_MH_axon_threads
• Mainline code: /Code/Python/Axon/Axon/
• Modified: Microprocess, Component and Scheduler
  
• Added: threadedadaptivecommscomponent to ThreadedComponent.py
  
• Mainline code: /Code/Python/Axon/Axon/Tests
• Tests removed that were now inapplicable
• New tests added
• Updated components to use new API:
  
• /Sketches/MPS/backplane.py
• /Sketches/MPS/control_mix.py
• /Sketches/MPS/dj1.py
• /Sketches/MPS/dj2.py
• /Sketches/MPS/music.py

Realistic possibilities arising as a result of activity on this task

Need to make access to CAT threadsafe too.

Task Log

• 13 April 2006 : Added developer Matt
  
• 13 April 2006 : Task status changed to running
• 13 April 2006 : Matt : worked on private_MH_Axon_threads branch for Axon
• 02 May 2006 : Matt : completed development
  
• 03 May 2006 : Added developer Michael : to merge branch into mainline
• 04 May 2006 : Michael : Merge completed
• 04 May 2006 : Task status changed to completed
• 04 May 2006 : Removed developers Matt, Michael
• 22 February 2007 : Project Task Page created
  

Discussion

Distinction between activity-creators and non activity-creator components removed (the scheduler would stop if there wasn't at least one activity-creator microprocess running). This was no longer necessary as there was no longer a postman microprocess (a non activity-creator). Removing support for this from the scheduler simplified things, making implementing support for the new design threaded components (and later quiescence optimisations) easier.

-- Matt Hammond, 22 February 2007