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From "Kristian Waagan (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (DERBY-5328) The private fields of the NetServlet can be changed by multiple threads, giving rise to race conditions and corruptions.
Date Mon, 02 Apr 2012 11:09:22 GMT

     [ https://issues.apache.org/jira/browse/DERBY-5328?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Kristian Waagan updated DERBY-5328:
-----------------------------------

    Attachment: derby-5328-02-aa-synchronized_doget.diff

Attaching patch 02-aa, which makes the doGet-method synchronized.
As mentioned earlier this is normally not something one would do for a servlet, but in this
case it seems appropriate. We only want to allow for one "admin request" to the network server
instance at a time.

I plan to commit this patch shortly.
                
> The private fields of the NetServlet can be changed by multiple threads, giving rise
to race conditions and corruptions.
> ------------------------------------------------------------------------------------------------------------------------
>
>                 Key: DERBY-5328
>                 URL: https://issues.apache.org/jira/browse/DERBY-5328
>             Project: Derby
>          Issue Type: Bug
>          Components: Network Server
>    Affects Versions: 10.9.0.0
>            Reporter: Rick Hillegas
>              Labels: derby_triage10_9
>         Attachments: derby-5328-01-aa-simpleFields.diff, derby-5328-02-aa-synchronized_doget.diff
>
>
> At the beginning of the NetServlet class, there are a number of private fields. These
fields can be inspected and changed by any thread running inside NetServlet.doGet(). Due to
the way that app servers dispatch servlet requests, this means that multiple threads can be
operating inside doGet() at the same time, clobbering one another's work. The weirdest instance
of this is the shared PrintWriter (called "out") which is used to produce the response web
page sent back by the servlet. Multiple threads all writing to the same PrintWriter will create
a very bizarre response page. The following improvements should be made:
> 1) The "server" field should be set by a synchronized method.
> 2) Every run through doGet() should create its own PrintWriter which is passed to other
methods. The instance-wide "out" field should be removed.
> 3) Various other fields should be re-coded using the Atomic classes introduced by Java
5. These fields include "logStatus" and "traceStatus". This solution can be implemented if
the community votes to approve the sunsetting of JVM 1.4 (currently at the polls).

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