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Three examples are presented: code snippets for visualizing the transition between active objects and components, the 'hello world', from the Fractal tutorial, and C3D component version. The programming model is Fractal, and one should refer to the Fractal documentation for other detailed examples.
In Java, objects are created by instantiation of classes. With ProActive, one can create active objects from Java classes, while components are created from component definitions. Let us first consider the 'A' interface:
public interface A { public String foo(); // dummy method }
'AImpl' is the class implementing this interface:
public class AImpl implements A { public AImpl() {} public String foo() { // do something } }
The class is then instantiated in a standard way:
A object = new AImpl();
Active objects are instantiated using factory methods from the ProActive class (see Section 13.10, “The Hello world example”). It is also possible to specify the activity of the active object, the location (node or virtual node), or a factory for meta-objects, using the appropriate factory method.
A active_object = (A)ProActive.newActive( AImpl, // signature of the base class new Object[] {}, // Object[] aNode, // location, could also be a virtual node );
As components are also active objects in this implementation, they benefit from the same features, and are configurable in a similar way. Constructor parameters, nodes, activity, or factories, that can be specified for active objects, are also specifiable for components. The definition of a component requires 3 sub-definitions: the type, the description of the content, and the description of the controller.
The type of the component (i.e. the functional interfaces provided and required) is specified in a standard way: (as taken from the Fractal tutorial)
We begin by creating objects that represent the types of the components of the application. In order to do this, we must first get a bootstrap component. The standard way to do this is the following one (this method creates an instance of the class specified in the fractal.provider system property, and uses this instance to get the bootstrap component):
Component boot = Fractal.getBootstrapComponent();
We then get the TypeFactory interface provided by this bootstrap component:
TypeFactory tf = (TypeFactory)boot.getFcInterface('type-factory');
We can then create the type of the first component, which only provides a A server interface named 'a':
// type of the a component ComponentType aType = tf.createFcType(new InterfaceType[] { tf.createFcItfType('a', 'A', false, false, false) });
The second step in the definition of a component is the definition of its content. In this implementation, this is done through the ContentDescription class:
ContentDescription contentDesc = new ContentDescription( AImpl, // signature of the base class new Object[] {}, // Object[] aNode // location, could also be a virtual node );
Properties relative to the controller can be specified in the ControllerDescription:
ControllerDescription controllerDesc = new ControllerDescription( 'myName', // name of the component Constants.PRIMITIVE // the hierarchical type of the component // it could be PRIMITIVE, COMPOSITE, or PARALLEL );
Eventually, the component definition is instantiated using the standard Fractal API. This component can then be manipulated as any other Fractal component.
Component component = componentFactory.newFcInstance( componentType, // type of the component (defining the client and server interfaces) controllerDesc, // implementation-specific description for the controller contentDesc // implementation-specific description for the content );
There are 2 kinds of interfaces for a component: those that offer services, and those that require services. They are named respectively server and client interfaces.
From a Java class, it is fairly natural to identify server interfaces: they (can) correspond to the Java interfaces implemented by the class. In the above example, 'a' is the name of an interface provided by the component, corresponding to the 'A' Java interface.
On the other hand, client interfaces usually correspond to attributes of the class, in the case of a primitive component. If the component defined above requires a service from another component, say the one corresponding to the 'Service' Java interface, the AImpl class should be modified. As we use the inversion of control pattern, a BindingController is provided, and a binding operation on the 'requiredService' interface will actually set the value of the 'service' attribute, of type 'Service'.
First, the type of the component is changed:
// type of the a component ComponentType aType = tf.createFcType(new InterfaceType[] { tf.createFcItfType('a', 'A', false, false, false), tf.createFcItfType('requiredService', 'A', true, false, false) });
The Service interface is the following:
And the AImpl class is:
// The modified AImpl class public class AImpl implements A, BindingController { Service service; // attribute corresponding to a client interface public AImpl() {} // implementation of the A interface public String foo() { return service.bar(); // for example } // implementation of BindingController public Object lookupFc (final String cItf) { if (cItf.equals('requiredService')) { return service; } return null; } // implementation of BindingController public void bindFc (final String cItf, final Object sItf) { if (cItf.equals('requiredService')) { service = (Service)sItf; } } // implementation of BindingController public void unbindFc (final String cItf) { if (cItf.equals('requiredService')) { service = null; } } }
The mandatory helloworld example (from the Fractal tutorial) shows the different ways of creating a component system (programmatically and using the ADL), and it can easily be implemented using ProActive.
You can find the code for this example in the package org.objectweb.proactive.examples.components.helloworld of the ProActive distribution.
The code is almost identical to the Fractal tutorial's example.
The differences are the following:
The reference example is provided for level 3.3. implementation, whereas this current implementation is compliant up to level 3.2: templates are not provided. Thus you will have to skip the specific code for templates.
The newFcInstance method of the
GenericFactory interface, used for directly
creating components, takes 2 implementation-specific parameters. So
you should use the
org.objectweb.proactive.component.ControllerDescription
and
org.objectweb.proactive.component.ContentDescription
classes to define ProActive components. (It is possible to use the
same parameters than in Julia, but that hinders you from using some
functionalities specific to ProActive, such as distributed
deployment or definition of the activity).
Collective interfaces could be implemented the same way than
suggested, but using the
Fractive.createCollectiveClientInterface method
will prove useful with this implementation: you are then able to use
the functionalities provided by the typed groups API.
Components can be distributed
the ClientImpl provides an empty no-args constructor.
The helloworld example is a simple client-server application, where the client (c) and the server (s) are components, and they are both contained in the same root component (root).
Another configuration is also possible, where client and server are wrapped around composite components (C and S). The goal was initially to show the interception shortcut mechanism in Julia. In the current ProActive implementation, there are no such shortcuts, as the different components can be distributed, and all invocations are intercepted. The exercise is still of interest, as it involves composite components.
This section is specific to the ProActive implementation, as it uses the deployment framework of this library.
If the application is started with (only) the parameter 'distributed', the ADL used is 'helloworld-distributed-no-wrappers.fractal', where virtualNode of the client and server components are exported as VN1 and VN2. Exported virtual node names from the ADL match those defined in the deployment descriptor 'deployment.xml'.
One can of course customize the deployment descriptor and deploy components onto virtually any computer, provided it is connectable by supported protocols. Supported protocols include LAN, clusters and Grid protocols (see Chapter 21, XML Deployment Descriptors).
Have a look at the ADL files 'helloworld-distributed-no-wrappers.fractal' and 'helloworld-distributed-wrappers.fractal'. In a nutshell, they say: 'the primitive components of the application (client and server) will run on given exported virtual nodes, whereas the other components (wrappers, root component) will run on the current JVM.
Therefore, we have the two following configurations:
Currently, bindings are not optimized. For example, in the configuration with wrappers, there is an indirection that can be costly, between the client and the server. We are currently working on optimizations that would allow to shortcut communications, while still allowing coherent dynamic reconfiguration. It is the same idea than in Julia, but we are dealing here with distributed components. It could imply compromises between dynamicity and performance issues.
You can either compile and run the code yourself, or follow the instructions for preparing the examples and use the script helloworld_fractal.sh (or .bat). If you choose the first solution, do not forget to set the fractal.provider system property.
If you run the program with no arguments (i.e. not using the parser, no wrapper composite components, and local deployment) , you should get something like this:
01 --> This ClassFileServer is reading resources from classpath 02 Jini enabled 03 Ibis enabled 04 Created a new registry on port 1099 05 //crusoe.inria.fr/Node363257273 successfully bound in registry at //crusoe.inria.fr/Node363257273 06 Generating class: pa.stub.org.objectweb.proactive.core.component.type.Stub_Composite 07 Generating class: pa.stub.org.objectweb.proactive.examples.components.helloworld.Stub_ClientImpl 08 Generating class: pa.stub.org.objectweb.proactive.examples.components.helloworld.Stub_ServerImpl
You can see:
line 01: the creation of the class file server which handles the on-the-fly generation and distribution of ProActive stubs and component functional interfaces
line 04: the creation of a rmi registry
line 05: the registration of the default runtime node
line 06 to 08: the on-the-fly generation of ProActive stubs (the generation of component functional interfaces is silent)
Then you have (the exception that pops out is actually the expected result, and is intended to show the execution path):
01 Server: print method called 02 at org.objectweb.proactive.examples.components.helloworld.ServerImpl.print(ServerImpl.java:37) 03 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 04 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) 05 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) 06 at java.lang.reflect.Method.invoke(Method.java:324) 07 at org.objectweb.proactive.core.mop.MethodCall.execute(MethodCall.java:373) 08 at org.objectweb.proactive.core.component.request.ComponentRequestImpl.serveInternal(ComponentRequestImpl.java:163) 09 at org.objectweb.proactive.core.body.request.RequestImpl.serve(RequestImpl.java:108) 10 at org.objectweb.proactive.core.body.BodyImpl$ActiveLocalBodyStrategy.serve(BodyImpl.java:297) 11 at org.objectweb.proactive.core.body.AbstractBody.serve(AbstractBody.java:799) 12 at org.objectweb.proactive.core.body.ActiveBody$FIFORunActive.runActivity(ActiveBody.java:230) 13 at org.objectweb.proactive.core.body.ActiveBody.run(ActiveBody.java:145) 14 at java.lang.Thread.run(Thread.java:534) 15 Server: begin printing... 16 --------> hello world 17 Server: print done.
What can be seen is very different from the output you would get with the Julia implementation. Here is what happens (from bottom to top of the stack):
line 14: The active object runs its activity in its own Thread
line 12: The default activity is to serve incoming request in a FIFO order
line 08: Requests (reified method calls) are encapsulated in ComponentRequestImpl objects
line 06: A request is served using reflection
line 02: The method invoked is the print method of an instance of ServerImpl
Now let us have a look at the distributed deployment: execute the program with the parameters 'distributed parser'. You should get something similar to the following:
01 --> This ClassFileServer is reading resources from classpath 02 Jini enabled 03 Ibis enabled 04 Created a new registry on port 1099 05 ************* Reading deployment descriptor: file:/0/user/mmorel/ProActive/classes/org/objectweb/proactive/examplescomponents/helloworld/deployment\ .xml ******************** 06 created VirtualNode name=VN1 07 created VirtualNode name=VN2 08 created VirtualNode name=VN3 09 **** Starting jvm on crusoe.inria.fr 10 --> This ClassFileServer is reading resources from classpath 11 Jini enabled 12 Ibis enabled 13 Detected an existing RMI Registry on port 1099 14 //crusoe.inria.fr/VN1462549848 successfully bound in registry at //crusoe.inria.fr/VN1462549848 15 **** Mapping VirtualNode VN1 with Node: //crusoe.inria.fr/VN1462549848 done 16 Generating class: pa.stub.org.objectweb.proactive.examples.components.helloworld.Stub_ClientImpl 17 **** Starting jvm on crusoe.inria.fr 18 --> This ClassFileServer is reading resources from classpath 19 Jini enabled 20 Ibis enabled 21 Detected an existing RMI Registry on port 1099 22 //crusoe.inria.fr/VN21334775605 successfully bound in registry at //crusoe.inria.fr/VN21334775605 23 **** Mapping VirtualNode VN2 with Node: //crusoe.inria.fr/VN21334775605 done 24 Generating class: pa.stub.org.objectweb.proactive.examples.components.helloworld.Stub_ServerImpl 25 //crusoe.inria.fr/Node1145479146 successfully bound in registry at //crusoe.inria.fr/Node1145479146 26 Generating class: pa.stub.org.objectweb.proactive.core.component.type.Stub_Composite 27 MOPClassLoader: class not found, trying to generate it 28 ClassServer sent class Generated_java_lang_Runnable_r_representative successfully 39 MOPClassLoader: class not found, trying to generate it 30 ClassServer sent class Generated_java_lang_Runnable_r_representative successfully 31 MOPClassLoader: class not found, trying to generate it 32 ClassServer sent class Generated_org_objectweb_proactive_examples_components_helloworld_Service_s_representative successfully 33 MOPClassLoader: class not found, trying to generate it 34 ClassServer sent class Generated_org_objectweb_proactive_examples_components_helloworld_ServiceAttributes_attribute_controller_representative succe\ ssfully 35 ClassServer sent class pa.stub.org.objectweb.proactive.examples.components.helloworld.Stub_ServerImpl successfully
What is new is:
line 05 the parsing of the deployment descriptor
line 09 and 17: the creation of 2 virtual machines on the host 'crusoe.inria.fr'
line 15 and 24: the mapping of virtual nodes VN1 and VN2 to the nodes specified in the deployment descriptor
line 35: the dynamic downloading of the stub class for ServerImpl: the stub class loader does not find the classes of the stubs in the current VM, and fetches the classes from the ClassServer
line 28, 30, 32, 34: the dynamic downloading of the classes corresponding to the components functional interfaces (they were silently generated)
Then we get the same output than for a local deployment, the activity of active objects is independent from its location.
01 Server: print method called 02 at org.objectweb.proactive.examples.components.helloworld.ServerImpl.print(ServerImpl.java:37) 03 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 04 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) 05 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) 06 at java.lang.reflect.Method.invoke(Method.java:324) 07 at org.objectweb.proactive.core.mop.MethodCall.execute(MethodCall.java:373) 08 at org.objectweb.proactive.core.component.request.ComponentRequestImpl.serveInternal(ComponentRequestImpl.java:163) 09 at org.objectweb.proactive.core.body.request.RequestImpl.serve(RequestImpl.java:108) 10 at org.objectweb.proactive.core.body.BodyImpl$ActiveLocalBodyStrategy.serve(BodyImpl.java:297) 11 at org.objectweb.proactive.core.body.AbstractBody.serve(AbstractBody.java:799) 12 at org.objectweb.proactive.core.body.ActiveBody$FIFORunActive.runActivity(ActiveBody.java:230) 13 at org.objectweb.proactive.core.body.ActiveBody.run(ActiveBody.java:145) 14 at java.lang.Thread.run(Thread.java:534) 15 Server: begin printing... 16 ->hello world 17 Server: print done.
org.objectweb.proactive.examples.components.helloworld.helloworld-distributed-wrappers.fractal
<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE definition PUBLIC "-//objectweb.org//DTD Fractal ADL 2.0//EN"
"classpath://org/objectweb/proactive/core/component/adl/xml/proactive.dtd">
<definition name=
"org.objectweb.proactive.examples.components.helloworld.helloworld-distributed-wrappers">
<interface name="r" role="server" signature="java.lang.Runnable"/>
<exportedVirtualNodes>
<exportedVirtualNode name="VN1">
<composedFrom>
<composingVirtualNode component="client" name="client-node"/>
</composedFrom>
</exportedVirtualNode>
<exportedVirtualNode name="VN2">
<composedFrom>
<composingVirtualNode component="server" name="server-node"/>
</composedFrom>
</exportedVirtualNode>
</exportedVirtualNodes>
<component name="client-wrapper" definition=
"org.objectweb.proactive.examples.components.helloworld.ClientType">
<component name="client" definition=
"org.objectweb.proactive.examples.components.helloworld.ClientImpl"/>
<binding client="this.r" server="client.r"/>
<binding client="client.s" server="this.s"/>
<controller desc="composite"/>
</component>
<component name="server-wrapper" definition=
"org.objectweb.proactive.examples.components.helloworld.ServerType">
<component name="server" definition=
"org.objectweb.proactive.examples.components.helloworld.ServerImpl"/>
<binding client="this.s" server="server.s"/>
<controller desc="composite"/>
</component>
<binding client="this.r" server="client-wrapper.r"/>
<binding client="client-wrapper.s" server="server-wrapper.s"/>
</definition>
org.objectweb.proactive.examples.components.helloworld.ClientType.fractal
<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE definition PUBLIC "-//objectweb.org//DTD Fractal ADL 2.0//EN"
"classpath://org/objectweb/proactive/core/component/adl/xml/proactive.dtd">
<definition name="org.objectweb.proactive.examples.components.helloworld.ClientType" extends=
"org.objectweb.proactive.examples.components.helloworld.RootType">
<interface name="r" role="server" signature="java.lang.Runnable"/>
<interface name="s" role="client" signature=
"org.objectweb.proactive.examples.components.helloworld.Service"/>
</definition>
org.objectweb.proactive.examples.components.helloworld.ClientImpl.fractal
<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE definition PUBLIC "-//objectweb.org//DTD Fractal ADL 2.0//EN"
"classpath://org/objectweb/proactive/core/component/adl/xml/proactive.dtd">
<definition name="org.objectweb.proactive.examples.components.helloworld.ClientImpl" extends=
"org.objectweb.proactive.examples.components.helloworld.ClientType">
<exportedVirtualNodes>
<exportedVirtualNode name="client-node">
<composedFrom>
<composingVirtualNode component="this" name="client-node"/>
</composedFrom>
</exportedVirtualNode>
</exportedVirtualNodes>
<content class="org.objectweb.proactive.examples.components.helloworld.ClientImpl"/>
<virtual-node name="client-node" cardinality="single"/>
</definition>
org.objectweb.proactive.examples.components.ServerType
<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE definition PUBLIC "-//objectweb.org//DTD Fractal ADL 2.0//EN"
"classpath://org/objectweb/proactive/core/component/adl/xml/proactive.dtd">
<definition name="org.objectweb.proactive.examples.components.helloworld.ServerType">
<interface name="s" role="server" signature=
"org.objectweb.proactive.examples.components.helloworld.Service"/>
</definition>
org.objectweb.proactive.examples.components.helloworld.ServerImpl
<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE definition PUBLIC "-//objectweb.org//DTD Fractal ADL 2.0//EN"
"classpath://org/objectweb/proactive/core/component/adl/xml/proactive.dtd">
<definition name="org.objectweb.proactive.examples.components.helloworld.ServerImpl" extends=
"org.objectweb.proactive.examples.components.helloworld.ServerType">
<exportedVirtualNodes>
<exportedVirtualNode name="server-node">
<composedFrom>
<composingVirtualNode component="this" name="server-node"/>
</composedFrom>
</exportedVirtualNode>
</exportedVirtualNodes>
<content class="org.objectweb.proactive.examples.components.helloworld.ServerImpl"/>
<attributes signature=
"org.objectweb.proactive.examples.components.helloworld.ServiceAttributes">
<attribute name="header" value="->"/>
<attribute name="count" value="1"/>
</attributes>
<controller desc="primitive"/>
<virtual-node name="server-node" cardinality="single"/>
</definition>
The Comanche example is a nice introduction to component based development with Fractal. It explains how to design applications using components, and how to implement these applications using the Fractal API.
You will notice that the example presented in this tutorial is based
on Comanche, a simplistic http server. However, this example extensively
uses reference passing through components. For example
Request objects are passed by reference. This is
incompatible with the ProActive programming model, where, to avoid shared
passive objects, all passive objects passed to active objects are actually
passed by copy
(see Chapter 12, ProActive Basis, Active Object Definition). As active objects are themselves passed by
reference, one could argue that we could turn some passive object into
active objects. This would allow remote referencing through stubs.
Unfortunately, for reasons specific to the Sockets and Streams
implementations, (Socket streams implementations do not provide empty
no-arg constructors), it is not easily possible to encapsulate some of the
needed resource classes into active objects.
There is a complete example of migrative Active Object code to Component code. This can be seen in the Guided Tour: Chapter 10, C3D - from Active Objects to Components.
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