iPOPO Components

A component is an object with a life-cycle, requiring services and providing ones, and associated to properties. The code of a component is reduced to its functional purpose: its life-cycle, dependencies, etc. are handled by iPOPO. In iPOPO, a component is an instance of component factory, i.e. a Python class manipulated with the iPOPO decorators.

Note

Due to the use of Python properties, all component factories must be new-style classes. It is the case of all Python 3 classes, but Python 2.x classes must explicitly inherit from the object class.

Life-cycle

The component life cycle is handled by an instance manager created by the iPOPO service. This instance manager will inject control methods, run-time dependencies, and will register the component services. All changes will be notified to the component using the callback methods it decorated.

iPOPO component life-cycle graph
State Description
INSTANTIATED The component has been instantiated. Its constructor has been called and the control methods have been injected
VALIDATED All required dependencies have been injected. All services provided by the component will be registered right after this method returned
KILLED The component has been invalidated and won’t be usable again
ERRONEOUS The component raised an error during its validation. It is not destroyed and a validation can be retried manually

API

iPOPO components are handled through the iPOPO core service, which can itself be accessed through the Pelix API or the utility context manager use_ipopo(). The core service provides the pelix.ipopo.core specification.

pelix.ipopo.constants.use_ipopo(*args, **kwds)

Utility context to use the iPOPO service safely in a “with” block. It looks after the the iPOPO service and releases its reference when exiting the context.

Parameters:bundle_context – The calling bundle context
Returns:The iPOPO service
Raises:BundleException – Service not found

The following snippet shows how to use this method:

from pelix.ipopo.constants import use_ipopo

# ... considering "context" being a BundleContext object
with use_ipopo(context) as ipopo:
    # use the iPOPO core service with the "ipopo" variable
    ipopo.instantiate("my.factory", "my.component",
                      {"some.property": [1, 2, 3], "answer": 42})

# ... out of the "with" context, the iPOPO service has been released
# and shouldn't be used

Here are the most commonly used methods from the iPOPO core service to handle components and factories:

class pelix.ipopo.core._IPopoService(bundle_context)

The iPOPO registry and service

Parameters:bundle_context – The iPOPO bundle context
add_listener(listener)

Register an iPOPO event listener.

The event listener must have a method with the following prototype:

def handle_ipopo_event(self, event):
    '''
    event: A IPopoEvent object
    '''
    # ...
Parameters:listener – The listener to register
Returns:True if the listener has been added to the registry
get_factories()

Retrieves the names of the registered factories

Returns:A list of factories. Can be empty.
get_factory_details(name)

Retrieves a dictionary with details about the given factory

  • name: The factory name
  • bundle: The Bundle object of the bundle providing the factory
  • properties: Copy of the components properties defined by the factory
  • requirements: List of the requirements defined by the factory
    • id: Requirement ID (field where it is injected)
    • specification: Specification of the required service
    • aggregate: If True, multiple services will be injected
    • optional: If True, the requirement is optional
  • services: List of the specifications of the services provided by components of this factory
  • handlers: Dictionary of the non-built-in handlers required by this factory. The dictionary keys are handler IDs, and it contains a tuple with:
    • A copy of the configuration of the handler (0)
    • A flag indicating if the handler is present or not
Parameters:name – The name of a factory
Returns:A dictionary describing the factory
Raises:ValueError – Invalid factory
get_instance_details(name)

Retrieves a snapshot of the given component instance. The result dictionary has the following keys:

  • name: The component name
  • factory: The name of the component factory
  • bundle_id: The ID of the bundle providing the component factory
  • state: The current component state
  • services: A {Service ID → Service reference} dictionary, with all services provided by the component
  • dependencies: A dictionary associating field names with the following dictionary:
    • handler: The name of the type of the dependency handler
    • filter (optional): The requirement LDAP filter
    • optional: A flag indicating whether the requirement is optional or not
    • aggregate: A flag indicating whether the requirement is a set of services or not
    • binding: A list of the ServiceReference the component is bound to
  • properties: A dictionary key → value, with all properties of the component. The value is converted to its string representation, to avoid unexpected behaviors.
Parameters:name – The name of a component instance
Returns:A dictionary of details
Raises:ValueError – Invalid component name
get_instances()

Retrieves the list of the currently registered component instances

Returns:A list of (name, factory name, state) tuples.
instantiate(factory_name, name, properties=None)

Instantiates a component from the given factory, with the given name

Parameters:
  • factory_name – Name of the component factory
  • name – Name of the instance to be started
  • properties – Initial properties of the component instance
Returns:

The component instance

Raises:
  • TypeError – The given factory is unknown
  • ValueError – The given name or factory name is invalid, or an instance with the given name already exists
  • Exception – Something wrong occurred in the factory
kill(name)

Kills the given component

Parameters:name – Name of the component to kill
Raises:ValueError – Invalid component name
remove_listener(listener)

Unregister an iPOPO event listener.

Parameters:listener – The listener to register
Returns:True if the listener has been removed from the registry
retry_erroneous(name, properties_update=None)

Removes the ERRONEOUS state of the given component, and retries a validation

Parameters:
  • name – Name of the component to retry
  • properties_update – A dictionary to update the initial properties of the component
Returns:

The new state of the component

Raises:

ValueError – Invalid component name