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From Anders Engström (JIRA) <j...@apache.org>
Subject [jira] [Commented] (FELIX-5199) Race condition in HttpServiceFactory.getService() causing exception
Date Sun, 20 Mar 2016 20:48:33 GMT

    [ https://issues.apache.org/jira/browse/FELIX-5199?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15203515#comment-15203515

Anders Engström commented on FELIX-5199:

While investigating FELIX-5219 I ran into some issues that I believe is related to this patch.

If a {{ServiceTracker}} is opened and listening for {{HttpService}} (*before* {{HttpServiceFactory#start}}
have been called) the {{active}} flag in {{HttpServiceFactory#getService}} will never be {{!=
null}} (and the returned service will be {{null}}. 

The reason is that the ServiceTracker will get a callback to {{addingService}} synchronously
when the service-factory is registered (line 114 in {{HttpServiceFactory}}. At this point
the {{active}} flag is still {{false}} (it's set to {{true}} right after the registration.
If the ServiceTracker tries to resolve the service-reference in its {{addingService}} this
will call into {{HttpServiceFactory#getService}} - but {{active}} is false, so no service
is returned.

I tried setting {{active}} to true just before registering the HttpServiceFactory, and this
seemed to work - but perhaps that will lead to similar race conditions as in the original
code before this patch?

> Race condition in HttpServiceFactory.getService() causing exception
> -------------------------------------------------------------------
>                 Key: FELIX-5199
>                 URL: https://issues.apache.org/jira/browse/FELIX-5199
>             Project: Felix
>          Issue Type: Bug
>          Components: HTTP Service
>    Affects Versions: http.base-3.0.6
>            Reporter: David Bosschaert
>            Assignee: David Bosschaert
>             Fix For: http.base-3.0.8
>         Attachments: felix-5199.patch
> The HttpServiceFactory.getService() is as follows:
> {code}
>     public HttpService getService(final Bundle bundle, final ServiceRegistration<HttpService>
>     {
>         final ServletContext servletContext = this.context;
>         if ( servletContext != null ) {
>             return new PerBundleHttpServiceImpl(bundle,
>                     this.sharedHttpService,
>                     this.context,
>                     this.contextAttributeListenerManager,
>                     this.sharedContextAttributes,
>                     this.requestListenerManager,
>                     this.requestAttributeListenerManager);
>         }
>         return null;
>     }{code}
> However it is possible that this.context is set to {{null}} after the check for {{null}}
is done but before the constructor is called causing a null servlet context to be passed to

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