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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-5328) The private fields of the NetServlet can be changed by multiple threads, giving rise to race conditions and corruptions.
Date Wed, 13 Jul 2011 21:47:00 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5328?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13064889#comment-13064889
] 

Knut Anders Hatlen commented on DERBY-5328:
-------------------------------------------

> 1) The "server" field should be set by a synchronized method.

I don't think NetworkServerControl is thread-safe, so it's probably safer to create an instance
in doGet() and pass it to the other methods as an argument.

> 3) Various other fields should be re-coded using the Atomic classes introduced by Java
5.

If all we need is atomic get and set of these fields, and not compare-and-swap, just declaring
the fields volatile would suffice, I think.

> 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
>
> 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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