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https://issues.apache.org/jira/browse/DERBY-5328?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Rick Hillegas updated DERBY-5328:
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Attachment: derby-5328-01-aa-simpleFields.diff
Attaching derby-5328-01-aa-simpleFields.diff. This patch makes a number of
changes to improve the re-entrancy of the NetServlet:
1) Makes the following fields volatile: tracingDirectory, logStatus,
traceStatus.
2) Makes knownLang a constant.
3) Moves the following fields inside the doGet() method: locale, out.
This patch does not tackle the issue of what to do with the server field.
I have run the resulting NetServlet inside tomcat and accessed it from multiple
browser tabs. The browser pages continue to operate as expected: changes to a
field in one tab become visible in the other tab after you refresh the second
tab. However, I have not stressed NetServlet by forcing close races between the
two tabs.
Touches one file:
M java/drda/org/apache/derby/drda/NetServlet.java
> 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
> Attachments: derby-5328-01-aa-simpleFields.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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