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https://issues.apache.org/jira/browse/JEXL-414?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Holger Sunke updated JEXL-414:
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Description:
I found the SoftCache used from within the Jexcel class Engine to be very
relevant for overall performance (depending on the application) on the one
hand, but on the other hand it may suffer from race conditions.
While solid efford was taken to protect it from race conditions by surrounding
access using a ReadWriteLock, parallel read access actually do reach out on a
LinkedHashMap having set accessOrder=true. This means that on every potentially
parallel, non serialized invocation of LinkedHashMap#get the order of elements
is modified to bring the last accessed element down to the tail of the internal
linked list structure and modCount is incremented.
In our application rendering web templates, we observe multiple of 10000 access
on the SoftCache per page impression and multiple of 10 page impressions per
second per JVM instance.
Not sure whether this is result of race condition claimed above, in heapdumps
of that application I observed the LinkedHashMap used within SoftCache having a
size of ~9500 elements while the SoftCache#size is set to limit the cache to
5000 elements. Additionaly the LinkedHashMap#modCount shows up with arbitrary
giant positive or negative numbers, telling me it has overflown already after
some hours of application uptime.
was:
I found the SoftCache used from within the Jexcel class `Engine` to be very
relevant for overall performance (depending on the application) on the one
hand, but on the other hand it may suffer from race conditions.
While solid efford was taken to protect it from race conditions by surrounding
access using a `ReadWriteLock`, parallel read access actually do reach out on a
`LinkedHashMap` having set `accessOrder=true`. This means that on every
potentially parallel, non serialized invocation of `LinkedHashMap#get` the
order of elements is modified to bring the last accessed element down to the
tail of the internal linked list structure and `modCount` is incremented.
In our application rendering web templates, we observe multiple of 10000 access
on the SoftCache per page impression and multiple of 10 page impressions per
second per JVM instance.
Not sure whether this is result of race condition claimed above, in heapdumps
of that application I observed the `LinkedHashMap` used within `SoftCahce`
having a size of ~9500 elements while the `SoftCache#size` is set to limit the
cache to 5000 elements. Additionaly the `LinkedHashMap#modCount` shows up with
arbitrary giant positive or negative numbers, telling me it has overflown
already after some hours of application uptime.
> SoftCache may suffer from race conditions
> -----------------------------------------
>
> Key: JEXL-414
> URL: https://issues.apache.org/jira/browse/JEXL-414
> Project: Commons JEXL
> Issue Type: Bug
> Affects Versions: 3.3
> Reporter: Holger Sunke
> Priority: Major
>
> I found the SoftCache used from within the Jexcel class Engine to be very
> relevant for overall performance (depending on the application) on the one
> hand, but on the other hand it may suffer from race conditions.
> While solid efford was taken to protect it from race conditions by
> surrounding access using a ReadWriteLock, parallel read access actually do
> reach out on a LinkedHashMap having set accessOrder=true. This means that on
> every potentially parallel, non serialized invocation of LinkedHashMap#get
> the order of elements is modified to bring the last accessed element down to
> the tail of the internal linked list structure and modCount is incremented.
>
> In our application rendering web templates, we observe multiple of 10000
> access on the SoftCache per page impression and multiple of 10 page
> impressions per second per JVM instance.
> Not sure whether this is result of race condition claimed above, in heapdumps
> of that application I observed the LinkedHashMap used within SoftCache having
> a size of ~9500 elements while the SoftCache#size is set to limit the cache
> to 5000 elements. Additionaly the LinkedHashMap#modCount shows up with
> arbitrary giant positive or negative numbers, telling me it has overflown
> already after some hours of application uptime.
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