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https://issues.apache.org/jira/browse/NUTCH-471?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Enis Soztutar updated NUTCH-471:
Attachment: NutchBeanCreationSync_v2.patch
From http://www-128.ibm.com/developerworks/java/library/j-dcl.html
The bottom line is that double-checked locking, in whatever form, should not be
used because you cannot guarantee that it will work on any JVM implementation.
JSR-133 is addressing issues regarding the memory model, however,
double-checked locking will not be supported by the new memory model.
Therefore, you have two options:
* Accept the synchronization of a getInstance() method as shown in Listing
2.
* Forgo synchronization and use a static field.
We don't want to remise performance in NutchBean.get(), synchronization is not
a solution. Thus as Sami has suggested, i have written a ServetContextListener
and added NutchBean construction code there. And modified web.xml to register
the event listener class. Also In the servlet initialization, the Configuration
object is initialized and cached by NutchConfiguration, so we avoid the same
problem in NutchConfiguration.get().
i have tested the implementation and it seems OK.
Fix synchronization in NutchBean creation
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Key: NUTCH-471
URL: https://issues.apache.org/jira/browse/NUTCH-471
Project: Nutch
Issue Type: Bug
Components: searcher
Affects Versions: 1.0.0
Reporter: Enis Soztutar
Fix For: 1.0.0
Attachments: NutchBeanCreationSync_v1.patch,
NutchBeanCreationSync_v2.patch
NutchBean is created and then cached in servlet context. But
NutchBean.get(ServletContext app, Configuration conf) is not syncronized,
which causes more than one instance of the bean (and
DistributedSearch$Client) if servlet container is accessed rapidly during
startup.
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