Page Pool Limit exhausted when exception occurs (during PageAttached lifecycle)
on a link
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Key: TAP5-256
URL: https://issues.apache.org/jira/browse/TAP5-256
Project: Tapestry 5
Issue Type: Bug
Components: tapestry-core
Affects Versions: 5.0.15
Reporter: Carlo Simbag
Whenever an exception occurs on a linked page (PageA in the attached example
code), the size of the "inUse" LinkedList is never reset. The reason for this
is that Tapestry has no chance to mark the page causing the exception (PageA)
as dirty and add it to the request page cache. Therefore at the end of the
request, when the thread cleanup event occurs, the page in error is never
removed (when dirty) and released. However the requested page (PageB in the
attached JMeter test) is marked as dirty and added to the request page cache
and is subsequently removed and released.
I have attached a sample project which has 3 pages (PageA, PageB, and PageC).
On each page, there is side menu that links to PageA, B and C. In PageA
during the PageAttached lifecycle, I have added a Runtime exception (note that
in our production environment we are getting Connection reset exceptions). To
run this application, you need to do the following:
- Extract the attached tutorial1.zip
- mvn clean install
- mvn jetty:run
A Jmeter test (PagePoolLoadTest.jmx) has also been provided, to automatically
go to PageB and assert that the exception generated by PageA exists as part of
the response. The test has 20 concurrent users which should run successfully
during the first attempt. However, during the second attempt, the test should
fail because Tapestry will report that page pool limit exceeded for PageA
eventhough there are only 20 concurrent users.
The patch I applied to our production version of Tapestry (5.0.15) is to modify
the RequestpageCacheImpl get method to catch the RuntimeException and mark the
page as dirty and add it to the request page cache:
public Page get(String logicalPageName)
{
Page page = cache.get(logicalPageName);
if (page == null)
{
page = pagePool.checkout(logicalPageName);
try {
page.attached();
cache.put(logicalPageName, page);
} catch(RuntimeException e) {
page.incrementDirtyCount();
cache.put(logicalPageName, page);
throw e;
}
}
return page;
}
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