Axon.CoordinatingAssistantTracker

The co-ordinating assistant tracker is designed to allow components to register services and statistics they wish to make public to the rest of the system. Components can also query the co-ordinating assistant tracker to create linkages to specific services, and for specific global statistics.

• A co-ordinating assistant tracker is shared between several/all components
• Components can register an inbox as a service with a name
• Components can retrieve a service by its name

Accessing the Co-ordinating Assistant Tracker

Co-ordinating assistant trackers are designed to work in a singleton manner; accessible via a local or class interface (though this is not enforced).

The simplest way to obtain the global co-ordinating assistant tracker is via the getcat() class (static) method:

from Axon.CoordinatingAssistantTracker import coordinatingassistanttracker

theCAT = coordinatingassistanttracker.getcat()

The first time this method is called, the co-ordinating assistant tracker is created. Subsequent calls, wherever they are made from, return that same instance.

Services

Components can register a named inbox on a component as a named service. This provides a way for a component to provide a service for other components - an inbox that another component can look up and create a linkage to.

Registering a service is simple:

theComponent = MyComponentProvidingServiceOnItsInbox()
theComponent.activate()

theCAT = coordinatingassistanttracker.getcat()
theCAT.registerService("MY_SERVICE", theComponent, "inbox")

Another component can then retrieve the service:

theCAT = coordinatingassistanttracker.getcat()
(comp, inboxname) = theCAT.retrieveService("MY_SERVICE")

Because services are run by components - these by definition die and so also need to be de-registered:

theCAT = coordinatingassistanttracker.getcat()
theCAT.deRegisterService("MY_SERVICE")

Tracking global statistics

Microprocesses can also use the co-ordinating assistant tracker to log/retrieve statistics/information.

Use the trackValue() method to initially start tracking a value under a given name:

value = ...

theCAT = coordinatingassistanttracker.getcat()
theCAT.trackValue("MY_VALUE", value)

This can then be easily retrieved:

theCAT = coordinatingassistanttracker.getcat()
value= theCAT.retrieveValue("MY_VALUE")

Call the updateValue() method (not the trackValue() method) to update the value being tracked:

newvalue = ...

theCAT = coordinatingassistanttracker.getcat()
theCAT.updateValue("MY_VALUE", newvalue)

Hierarchy of co-ordinating assistant trackers

Although at initialisation a parent co-ordinating assistant tracker can be specified; this is not currently used.

Test documentation

Tests passed:

• __init__ - Trying to set a anything other than a coordinated assistant tracker as the parent causes a BadParentTracker exception
• __init__ - Called with no arguments should succeed.
• __init__ - Called with a single argument results in it being the parent for the tracker
• deRegisterService - allows a component to remove their service from being public
• deRegisterService - deleting a non-existant service raises MultipleServiceDeletion exception
• informationItemsLogged - returns the names of pieces of information logged with this tracker
• registerService - adds the named component/inbox to the list of named registered services
• registerService - adding a duplicate service fails, even with same arguments
• registerService - adding a service but not to as a component fails- raises BadComponent assertion
• registerService - adding a service but to a bad/nonexistant inbox fails - raises BadInbox assertion
• retrieveService - Retrieving a tracked service should return the component/inbox pair we supplied under a specific name
• retrieveService - Attempting to retrieve a non-tracked service results in KeyError exception being thrown
• retrieveValue - Retrieving a tracked value should return the value we asked to be tracked
• retrieveValue - attempting to retrieve a value we're not tracking should raise AccessToUndeclaredTrackedVariable
• trackValue - Adding a value to be tracked twice raises NamespaceClash
• trackValue - Adds the name/value pair to the set of info items logged
• updateValue - Updating a value should result in the value stored being updated
• updateValue - Updating a value not declared as tracked should raise AccessToUndeclaredTrackedVariable

coordinatingassistanttracker([parent]) -> new coordinatingassistanttracker object.

Co-ordinating assistant tracker object tracks values and (component,inboxname) services under names.

Keyword arguments:

• parent -- Optional. None, or a parent coordinatingassistanttracker object.