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https://issues.apache.org/jira/browse/FELIX-1546?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Marcel Offermans closed FELIX-1546.
-----------------------------------
Part of the 3.0.0 release.
> DM/Temporal Dependency/Bound Service Replacement features
> ---------------------------------------------------------
>
> Key: FELIX-1546
> URL: https://issues.apache.org/jira/browse/FELIX-1546
> Project: Felix
> Issue Type: New Feature
> Components: Dependency Manager
> Reporter: Pierre De Rop
> Assignee: Marcel Offermans
> Priority: Minor
> Attachments: DM-1.tgz, DM-2-test.tgz, DM-2.tgz, DM-3.tgz, DM-4.tgz,
> DM-test.tgz, DM.tgz
>
>
> This issue proposes some new features for DM:
> Feature 1): dealing with service dynamics: Temporal dependencies
> ----------------------------------------------------------------
>
> So far, with DM, when a service looses one of its required dependencies, the
> service is
> deactivated. For stateless required dependencies, it would then be nice to
> support a temporal
> required dependency, which blocks the caller thread while the dependency is
> being updated.
> In the attached DM.tgz patch, you will find a new
> "TemporalServiceDependency.java" class, which extends the
> "ServiceDependency" class. In TemporalServiceDependency.java, you'll find a
> setTimeout method
> which takes a timeout parameter, in millis, specifying the max time to wait
> (30 seconds by
> default). After timeout, an unchecked "ServiceUnavailableException" is fired
> to the caller
> thread.
> Here is a more specific description of what the new
> "TemporalServiceDependency" class is doing
> exactly:
> The class actually uses a Dynamic Proxy which wraps the actual service
> dependency
> instance. When the service is lost, we check if there is an available
> replacement service from the
> tracker. If true, then we just update our internal service with the new one.
> If false, then we set
> a flag, which blocks any thread that invokes the service through the Dynamic
> Proxy. On timeout,
> we raise an unchecked ServiceUnavailableException, telling that the required
> service is unavailable (but we
> don't deactivate the service). The next time the dependency is invoked and if
> the service has come
> up, then the method will invoke the new service transparently.
> Using setTimeout(0) is supported: The thread won't be blocked, but will catch
> the unchecked
> exception immediately, in case of service loss.
> Of course, I don't pretend here to propose a feature as powerful as iPOJO
> "temporal dependencies"
> or Blueprint specification. However, you will see that the proposed patch is
> somewhat
> lightweight and is just fine for Dependency Manager.
> For example, Here is an example ->
> dm.add(createService()
> .setImplementation(Client.class)
> .add(createTemporalServiceDependency()
> .setService(MyService.class) // AutoConfig
> .setTimeout(5000)));
> public class Client implements Runnable {
> private Thread _thread;
> private MyService _service; // Dynamic Proxy auto injected (AUTO CONFIG
> MODE)
> void start() {
> _thread = new Thread(this);
> _thread.start();
> }
> public void run() {
> while (true) {
> try {
> _service.doService(); // will block while myService is updated
> } catch (Throwable t) {
> t.printStackTrace(); // ServiceUnavailableException if the service is
> not here for more than 5 seconds
> }
> }
> }
> }
> One last note: this feature is only meaningful for stateless services, not
> for sateful
> services. But for stateless services, I think that it is cool to not
> re-activate the whole
> service while the dependency is updated. For stateful services, I don't think
> that temporal
> dependencies applies because we would then loose service internal states
> between updates ...
> One last note: in TemporalServiceDependency, I override returned type which
> is only supported in
> jdk 1.5.
> For instance, the TemporalServiceDependency.setTimeout is defined as this:
> public TemporalServiceDependency setTimeout( long timeout ) { ...}
> So, I am wondering if that would be possible to impose jdk 1.5 for the next
> version of DM ?
> Feature 2): dealing with Bound Service Replacement:
> ---------------------------------------------------
> We would like DM to be able to replace a lost required dependency, by another
> existing one (if
> available from the registry), but without deactivating the service.
> Currently, the service is
> deactivated when loosing one of its required dependencies. If, however, a
> replacement is
> available from tracker, we just would like invoke the "changed" service
> callback (instead of
> deactivating it).
> I know that in DeclarativeService, the "added", then the "removed" callback
> would be invoked, but
> I think It's much more intuitive to invoke the "changed" callback.
> For example, when a required service dependency is lost, DM could behave like
> the following:
> 1- lookup another service (which matches the lost service dependency filter).
> 2- If found, update the service (in AutoConfig mode), or invoke a "changed"
> callbacks.
> 3- Otherwise, if AutoConfig is turned off and there is no "changed" callback,
> then deactivate the
> service (like it is the case currently).
> The fix in located in the ServiceDependency.java (see removedService method).
> Notice that I also changed the makeUnavailable method.
> Feature 3): let the DM shell display service dependencies filters.
> -----------------------------------------------------------------------------
> Currently, the DM shell displays the service dependencies without the service
> filter. So that is
> problematic when a service have multiple dependencies on the same service,
> but with different
> filters.
> For example: when typing the command "dm", the patch is now displaying the
> following:
> [7] test.dm
> class test.Client registered
> test.Printer(color=true) service required available
> test.Printer(color=false) service required available
> The fix is located in ServiceDependency.java, in the getName() method, which
> appends the service
> filter after the service name. Notice that we don't display the 'objectClass'
> parameter.
> Auto Configuration vs Callbacks
> -------------------------------
> Well this is not a feature, but rather an improvement regarding the issue
> https://issues.apache.org/jira/browse/FELIX-1278
> Recently, you fixed the issue FELIX-1278, where we asked to turn off autoconf
> when setCallbacks is invoked
> (thank you for the fix !).
> However, I think we forgot to ask you to not turn off autoconfig if both
> setCallback /
> setAutoConfig(true) are invoked. Indeed, in some times, it may make sense to
> use both methods,
> like this: ->
> dm.add(createServiceDependency()
> .setService(MyService.class)
> .setRequired(false)
> .setAutoConfig("_field")
> .setCallbacks("add", "remove"));
> Here, we inject an optional configuration in AutoConfig mode (field
> injection), but we also
> provide a callback method to be able to handle new services (after
> activation).
> You could tell me that with the current svn fix, we could invoke setCallbacks
> BEFORE
> setAutoConfig. But I just added a flag when
> setAutoConfig method is called explicitly (in order to avoid turning off auto
> config from
> setCallbacks method). The fix in located in ServideDependency.java
> Regards;
> /pierre
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