Hi *,
Hope all is well.
Michael and I have spent the day testing our C2 application with
LoadRunner and have potentially uncovered a threading problem during
sitemap creation.
We're not experts with the code but from our understanding the
following is happening, please let us know if we are right/wrong:
There seems to be a problem with the getHandler() method, located in
the sitemap Manager class (line 154). getHandler() attempts to access a
sitemap handler object for each request for processing. If the handler
object is not available it creates one, causing the sitemap to be
generated.
We've noticed under load, that many handler objects are created for
the same sitemap. This is because getHandler() does not protect the
following lines:
Handler sitemapHandler = (Handler)sitemaps.get(source);
and
sitemaps.put(source, sitemapHandler);
as a critical area.
If multiple concurrent threads pass through getHandler() which are
requests for resources from the same sitemap, the first line
above will return null multiple times causing the same sitemap to be
compiled several times, each by individual Handler objects.
This happens because sitemaps.put() executes after each sitemap handler
object is created (which can take time for large sitemaps), and cannot
prevent other incoming threads from waiting until it adds the newly
created handler object into the 'sitemaps' hashmap.
When we synchronized the getHandler method to protect the
getting/setting of the sitemaps hashmap, we saw that the sitemap
handler object was created only once, and that the application
performed much better under load. Previously the same sitemap handler
object was created as many times as we had simultaneous threads
make requests.
Attached is a diff of the change we made. There might be a better
solution as the Handler class seems to be built to handle this, it's
just that the allocation of a new Handler objects per sitemap, defeats
it's internal multi-thread logic.
Any comments/thoughts/suggestions ?
Cheers,
Marcus
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Index: Manager.java
===================================================================
RCS file: /home/cvspublic/xml-cocoon2/src/org/apache/cocoon/sitemap/Manager.java,v
retrieving revision 1.7
diff -u -r1.7 Manager.java
--- Manager.java 2001/07/12 12:28:19 1.7
+++ Manager.java 2001/08/18 20:13:12
@@ -151,7 +151,7 @@
}
*/
- private Handler getHandler(final ComponentManager newManager, final Environment
environment, final String source, final boolean check_reload,
+ private synchronized Handler getHandler(final ComponentManager newManager, final
+Environment environment, final String source, final boolean check_reload,
final boolean reload_asynchron) throws Exception {
Handler sitemapHandler = (Handler)sitemaps.get(source);
if (sitemapHandler != null) {
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