[jboss-jira] [JBoss JIRA] (WFCORE-3210) Wildfly module isolation not working consistently

[James Perkins (JIRA)]

    [ https://issues.jboss.org/browse/WFCORE-3210?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13454937#comment-13454937 ] 

James Perkins commented on WFCORE-3210:
---------------------------------------

Modules are definitely isolated to their own class loader. However when you add a log4j appender as a custom-handler to the logging subsystem it's going to use the {{org.apache.log4j}} module which effectively uses the {{org.jboss.log4j.logmanager}} module. Working around that may not be possible without changes to the logging subsystem. The logging subsystem itself, {{org.jboss.as.logging}} module, depends on {{org.apache.log4j}}.

Ideally instead of providing your own log4j library you just add a dependency to {{org.apache.log4j}} in your custom module. Instead of having {{<resource-root path="log4j-1.2.17.jar" />}} you just add a module dependency. Your module.xml should likely look more like the following:
{code:xml}
<?xml version="1.0" encoding="UTF-8"?>
<module xmlns="urn:jboss:module:1.1" name="company.logginglog4j1">
    <resources>
        <!-- Our appenders -->
        <resource-root path="company-logging-log4j-1.0.1.jar"/>
        <!-- Wildfly to log4j routing -->
        <resource-root path="company-wildfly-logging-tool-1.0.0-SNAPSHOT.jar"/>
        <!-- This could be interesting if we wanted to add log4j properties file in this folder to be looked up by the module code. -->
        <resource-root path="."/>
    </resources>
    <dependencies>
        <module name="org.apache.log4j"/>
    </dependencies>
</module>
{code}

I guess maybe I should ask this. With your custom-handler, does it implement a log4j Appender or a JUL Handler?

> Wildfly module isolation not working consistently
> -------------------------------------------------
>
>                 Key: WFCORE-3210
>                 URL: https://issues.jboss.org/browse/WFCORE-3210
>             Project: WildFly Core
>          Issue Type: Bug
>          Components: Logging, Modules
>    Affects Versions: 2.2.0.Final
>            Reporter: Nuno Godinho de Matos
>
> There is an underministic bug on the module layer of wildfly, whereby the boot logic of the application server is not ensured to give the appropriate module isolation - which can lead to unexpected boot classpath problems.
> An example of this phenomena is given on the wildfly forum thread:
> https://developer.jboss.org/thread/275839
> In this example, we have the logging subsystem setup to use a custome handler.
> The custom handler wishes to have acces to the JUL extension classes on the org.jboss.logmanger module, but wishes to do have no relationship with the org.apache.log4j packages associated to the wildfly org.jboss.log4j module.
> What we see in this example is that an application gets from wildfly mixed behavior.
> Most of the time, during boot, the processes works without problem, where the custom handler runs isolated from the undersired log4j libraries within wildfly.
> But other times the application boot procedure will not go smoothly with the custom handler having processes routing JUL LogRecords events into the bundled log4j because the application server has loaded some of the classes that exist the org.jboss.log4j module.
> And as we know when the same class is loaded by different class loaders, then that class that orinates from class loader A cannot be assigned to the corresponding class of class loader B, even if the classes are exactly the same.
> This is not an isolated issue.
> There are also open issues on the wildfly forum reporting on startup problems on the logging subsystme where sometimes the LogManager class had not yet been loaded, and sometimes this issue goes away.
> This is an indication of some deep issue engrained into the module loading, where the module isolation behavior is not ensured to work all the time and that the boot procedure is not deterministically reliable. 
> It should not be that the application server some time starts successfully and others not.
> Booting wildfly should always result in the same outcode.
> Problems of this nature with class loading problems should either always happen if the configuration is not done properly or never happen if the configuration is proper.
> In the case of thread:
> https://developer.jboss.org/thread/275839
> Our belief is that the configuration is doing all it possible can to request the necessary module isolation from base packages and the outcome where log4j class load problems take place should never be allowed to happen.
> Many thanks.



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