iPOPO 0.7.0

Usage survey

In order to gain insight from the iPOPO community, I’ve put a really short survey on Google Forms (no login required).

Please, feel free to answer it, the more answers, the better. All feedback is really appreciated, and I’ll write about the aggregated results on the users’ mailing list, once enough answers will have been received.

Option 1: Using pip

iPOPO is available on PyPI and can be installed using pip:

# Install system-wide
$ sudo pip install iPOPO

# ... or user-wide installation
$ pip install --user iPOPO

Option 2: From source

$ git clone https://github.com/tcalmant/ipopo.git
$ cd ipopo
$ python setup.py install

Check install

To check if Pelix is installed correctly, run the following command:

$ python -m pelix.shell --version
Pelix 0.7.0 from /home/tcalmant/git/ipopo/pelix/framework.py

Service provider

The following code defines a component factory (a class) which instances will provide a sample.hello service.

# iPOPO decorators
from pelix.ipopo.decorators import ComponentFactory, Provides, Instantiate

# Manipulates the class and sets its (unique) factory name
@ComponentFactory("hello-provider-factory")
# Indicate that the components will provide a service
@Provides("sample.hello")
# Tell iPOPO to instantiate a component instance as soon as the file is loaded
@Instantiate("hello-provider-auto")
# A component class must always inherit from object (new-style class)
class HelloProvider(object):
    """
    A sample service provider
    """
    def hello(self, name="world"):
        """
        Says hello
        """
        print("Hello,", name, "!")

    def bye(self, name="cruel world"):
        """
        Says bye
        """
        print("Bye,", name, "!")

When the bundle providing this component factory will be started, iPOPO will automatically instantiate a component, due to the @Instantiate decorator. It is also possible to instantiate a component using shell commands.

Each component instance will provide a sample.hello service, which can be consumed by any bundle or any other component.

Service consumer

The following code defines a component factory (a class) which instances will consume a sample.hello service. If multiple services are available, iPOPO will select the one with the highest rank and the lowest service ID (i.e. the oldest service).

# iPOPO decorators
from pelix.ipopo.decorators import ComponentFactory, Requires, Instantiate, \
    Validate, Invalidate

# Manipulates the class and sets its (unique) factory name
@ComponentFactory("hello-consumer-factory")
# Indicate that the components require a sample.hello service to work
# and to inject the found service in the _svc field
@Requires('_svc', "sample.hello")
# Tell iPOPO to instantiate a component instance as soon as the file is loaded
@Instantiate("hello-consumer-auto")
# A component class must always inherit from object (new-style class)
class HelloConsumer(object):
    """
    A sample service consumer
    """
    def __init__(self):
        """
        Defines (injected) members
        """
        self._svc = None

    @Validate
    def validate(self, context):
        """
        Component validated: all its requirements have been injected
        """
        self._svc.hello("Consumer")

    @Invalidate
    def invalidate(self, context):
        """
        Component invalidated: one of its requirements is going away
        """
        self._svc.bye("Consumer")

When the bundle providing this component factory will be started, iPOPO will automatically instantiate a component, due to the @Instantiate decorator.

Each component instance will require a sample.hello service. Once iPOPO has injected all the required services (here, a single sample.hello service) in a component instance, this instance will be considered valid and iPOPO will call its method decorated by @Validate. There, the component can consume its dependencies, start threads, etc.. It is recommended for this method to start threads and to return quickly, as it blocks iPOPO and the Pelix framework.

When a required service is unregistered by its provider, the component instances consuming it are invalidated. When the method decorated by @Invalidate is called, the service is still injected and should be usable (except for special cases, like remote services).

Run!

To run this sample, you’ll need to copy the snippets above in different files:

• copy the Service provider snippet in a file called provider.py

• copy the Service consumer snippet in a file called consumer.py

Then, run a Pelix shell in the same folder as those files, and execute the commands listed in this trace:

$ python -m pelix.shell
** Pelix Shell prompt **
$ # Install the bundles
$ install provider
Bundle ID: 11
$ install consumer
Bundle ID: 12
$ # Start the bundles (the order isn't important here)
$ start 11 12
Starting bundle 11 (provider)...
Starting bundle 12 (consumer)...
Hello, Consumer !
$ # View iPOPO instances
$ instances
+----------------------+------------------------------+-------+
|         Name         |           Factory            | State |
+======================+==============================+=======+
| hello-consumer-auto  | hello-consumer-factory       | VALID |
+----------------------+------------------------------+-------+
| hello-provider-auto  | hello-provider-factory       | VALID |
+----------------------+------------------------------+-------+
| ipopo-shell-commands | ipopo-shell-commands-factory | VALID |
+----------------------+------------------------------+-------+
3 components running
$ # View details about the consumer
$ instance hello-consumer-auto
Name.....: hello-consumer-auto
Factory..: hello-consumer-factory
Bundle ID: 12
State....: VALID
Services.:
Dependencies:
        Field: _svc
                Specification: sample.hello
                Filter......: None
                Optional.....: False
                Aggregate....: False
                Handler......: SimpleDependency
                Bindings:
                        ServiceReference(ID=11, Bundle=11, Specs=['sample.hello'])
Properties:
        +---------------+---------------------+
        |      Key      |        Value        |
        +===============+=====================+
        | instance.name | hello-consumer-auto |
        +---------------+---------------------+

$ # Modify the provider file (e.g. change the 'Hello' string by 'Hi')
$ # Update the provider bundle (ID: 11)
$ update 11
Updating bundle 11 (provider)...
Bye, Consumer !
Hi, Consumer !
$ # Play with other commands (see help)

First, the install commands are used to install the bundle: they will be imported but their activator won’t be called. If this command fails, the bundle is not installed and is not referenced by the framework.

If the installation succeeded, the bundle can be started: it’s activator is called (if any). Then, iPOPO detects the component factories provided by the bundle and instantiates the components declared using the @Instantiate decorator.

The instances and instance commands can be use to print the state and bindings of the components. Some other commands are very useful, like sl and sd to list the registered services and print their details. Use the help command to see which ones can be used.

The last part of the trace shows what happens when updating a bundle. First, update the source code of the provider bundle, e.g. by changing the string it prints in the hello() method. Then, tell the framework to update the bundle using the update command. This command requires a bundle ID, which has been given as a result of the install command and can be found using bl.

When updating a bundle, the framework stops it and reloads it (using imp.reload). If the update fails, the old version is kept. If the bundle was active before the update, it is restarted by the framework.

Stopping a bundle causes iPOPO to kill the component instance(s) of the factories it provided. Therefore, no one provides the sample.hello service, which causes the consumer component to be invalidated. When the provider bundle is restarted, a new provider component is instantiated and its service is injected in the consumer, which becomes valid again.