[Bug 57743] New: Jar files in /WEB-INF/lib are kept open, preventing redeploy

[bu...@apache.org]

https://bz.apache.org/bugzilla/show_bug.cgi?id=57743

            Bug ID: 57743
           Summary: Jar files in <webapp>/WEB-INF/lib are kept open,
                    preventing redeploy
           Product: Tomcat 8
           Version: 8.0.20
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Catalina
          Assignee: dev@tomcat.apache.org
          Reporter: pavel@semmle.com

Created attachment 32592
  --> https://bz.apache.org/bugzilla/attachment.cgi?id=32592&action=edit
A patch against AbstractResourceSet.java, adding a call to gc() when it is
destroyed.

As described in 56390, keeping jar files in a webapp folder open will prevent
the application from being undeployed/redeployed on file systems which don't
like open files to be deleted (in practice, that seems to mean Windows-based
systems or NFS mounts).

Having observed the problem with tomcat 8.0.20, which is meant to contain the
fix for 56390, I believe I have uncovered the root cause. Here's what happens,
in my scenario:

 - A new .war is copied into $CATALINA_HOME/webapps; this is picked up by
`HostConfig.checkResources()`, which decides to redeploy the app.

 - To do this, it first undeploys it (HostConfig.java:1250 in the TOMCAT_8_0_20
tag), and then attempts to delete the exploded war (line 1251).

 - In my case, the undeploy triggered a servlet's `destroy()` method, which
triggered some class loading from WEB-INF/lib. Thus, the context's
`WebResourceRoot` was used immediately before the attempt to delete the webapp
folder, and opened a jar file.

 - Even though the `JarInputStreamWrapper` was properly closed, the handle to
the jar remains open -- by design of `AbstractArchiveResource`, it is not
closed immediately but with the next periodically scheduled call to `gc()`, as
part of `StandardRoot.backgroundProcess()`.

As a result, when $CATALINA_HOME is on an NFS mount tomcat fails to delete the
exploded webapp directory, and things go bad.

The attached patch fixes the problem in my testing; it simply changes
`AbstractResourceSet.destroyInternal()` so that instead of doing nothing it
calls `gc()`, which will close any jar files which no longer have open input
streams. This seems like it's necessary to avoid a resource leak even on
systems that allow the deletion of open files, since if I'm not mistaken after
the context has been detached it will no longer receive `gc()` calls from the
background process thread.

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[Bug 57743] Jar files in /WEB-INF/lib are kept open, preventing redeploy

[bu...@apache.org]

https://bz.apache.org/bugzilla/show_bug.cgi?id=57743

Mark Thomas <ma...@apache.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #1 from Mark Thomas <ma...@apache.org> ---
Thanks for the very clear bug report and analysis.

Both the analysis and patch look good so the patch has been applied to trunk
and 8.0.x for 8.0.21 onwards.

Thanks again for your contribution.

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