[jira] [Commented] (POOL-213) _numActive can go negative
[ https://issues.apache.org/jira/browse/POOL-213?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanelfocusedCommentId=13240652#comment-13240652 ] Mark Mindenhall commented on POOL-213: -- It looks like 1.6 would solve the problem, but using 1.6 would require me to refactor the Hector code to use generics. _numActive can go negative -- Key: POOL-213 URL: https://issues.apache.org/jira/browse/POOL-213 Project: Commons Pool Issue Type: Bug Affects Versions: 1.5.4 Reporter: Mark Mindenhall I'm working on a project that uses Hector (Cassandra client). Hector uses commons-pool (we're using 1.5.4) to pool connections to hosts within a Cassandra cluster. Hector provides a JMX MBean that exposes a NumActive property, which is the cumulative call to retrieve numActive from all of the individual connection pools. When querying this property via JMS on our production servers, we often see negative values. For example, on a server that has three connection pools, the NumActive property reported was -3899. I know this issue has been reported before (POOL-29), and was supposedly fixed. The fix discussed there was to merely check the value of _numActive to prevent it from going negative. However, that does not fix the real problem here, which is that it is possible to decrement _numActive more than once for each activated object. For example, from a quick look at the code (GenericObjectPool.java, v1.5.4), it would be possible to do the following: 1) Create a pool with 10 objects. 2) Borrow all 10 objects from the pool. 3) Call getNumActive (returns 10). 4) Call invalidateObject for ONE of the objects 11 times. 5) Call getNumActive (returns -1). The invalidateObject method calls the _factory to destroy the object, and subsequent calls to destroy the same object may or may not result in an exception. Regardless, _numActive is decremented within a finally block, and therefore would always be decremented even if the object had already been invalidated and destroyed. I'd like to suggest using a HashSet instead of a counter to keep track of active objects. If borrowing an object added it to a HashSet, and returning or invaliding the object removed it from the HashSet (subsequent removes would be no-ops), the example given above would not result in an incorrect value when getNumActive is called (it would just return the current size of the HashSet). Note that although unrelated to this bug, it might also be wise to use a HashSet instead of the int counter _numInternalProcessing. -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators: https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa For more information on JIRA, see: http://www.atlassian.com/software/jira
[jira] [Commented] (POOL-213) _numActive can go negative
[ https://issues.apache.org/jira/browse/POOL-213?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanelfocusedCommentId=13240660#comment-13240660 ] Mark Mindenhall commented on POOL-213: -- Thanks, I'll try that...I figured something would break if I just dropped in the generics version. _numActive can go negative -- Key: POOL-213 URL: https://issues.apache.org/jira/browse/POOL-213 Project: Commons Pool Issue Type: Bug Affects Versions: 1.5.4 Reporter: Mark Mindenhall I'm working on a project that uses Hector (Cassandra client). Hector uses commons-pool (we're using 1.5.4) to pool connections to hosts within a Cassandra cluster. Hector provides a JMX MBean that exposes a NumActive property, which is the cumulative call to retrieve numActive from all of the individual connection pools. When querying this property via JMS on our production servers, we often see negative values. For example, on a server that has three connection pools, the NumActive property reported was -3899. I know this issue has been reported before (POOL-29), and was supposedly fixed. The fix discussed there was to merely check the value of _numActive to prevent it from going negative. However, that does not fix the real problem here, which is that it is possible to decrement _numActive more than once for each activated object. For example, from a quick look at the code (GenericObjectPool.java, v1.5.4), it would be possible to do the following: 1) Create a pool with 10 objects. 2) Borrow all 10 objects from the pool. 3) Call getNumActive (returns 10). 4) Call invalidateObject for ONE of the objects 11 times. 5) Call getNumActive (returns -1). The invalidateObject method calls the _factory to destroy the object, and subsequent calls to destroy the same object may or may not result in an exception. Regardless, _numActive is decremented within a finally block, and therefore would always be decremented even if the object had already been invalidated and destroyed. I'd like to suggest using a HashSet instead of a counter to keep track of active objects. If borrowing an object added it to a HashSet, and returning or invaliding the object removed it from the HashSet (subsequent removes would be no-ops), the example given above would not result in an incorrect value when getNumActive is called (it would just return the current size of the HashSet). Note that although unrelated to this bug, it might also be wise to use a HashSet instead of the int counter _numInternalProcessing. -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators: https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa For more information on JIRA, see: http://www.atlassian.com/software/jira
[jira] [Commented] (POOL-213) _numActive can go negative
[
https://issues.apache.org/jira/browse/POOL-213?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanelfocusedCommentId=13240805#comment-13240805
]
Mark Mindenhall commented on POOL-213:
--
I spoke too soon. The current 1.6 release (that can be downloaded) has exactly
the same problem with the invalidateObject method:
{code}
public void invalidateObject(T obj) throws Exception {
try {
if (_factory != null) {
_factory.destroyObject(obj);
}
} finally {
synchronized (this) {
_numActive--;
}
allocate();
}
}
{code}
When you suggested version 1.6, I looked at the version of GenericObjectPool in
trunk, which fixes the problem. What's the status of that release? It looks
like a major refactoring (even the package name has changed from
org.apache.commons.pool to org.apache.commons.pool2).
_numActive can go negative
--
Key: POOL-213
URL: https://issues.apache.org/jira/browse/POOL-213
Project: Commons Pool
Issue Type: Bug
Affects Versions: 1.5.4
Reporter: Mark Mindenhall
I'm working on a project that uses Hector (Cassandra client). Hector uses
commons-pool (we're using 1.5.4) to pool connections to hosts within a
Cassandra cluster. Hector provides a JMX MBean that exposes a NumActive
property, which is the cumulative call to retrieve numActive from all of the
individual connection pools. When querying this property via JMS on our
production servers, we often see negative values. For example, on a server
that has three connection pools, the NumActive property reported was -3899.
I know this issue has been reported before (POOL-29), and was supposedly
fixed. The fix discussed there was to merely check the value of _numActive
to prevent it from going negative. However, that does not fix the real
problem here, which is that it is possible to decrement _numActive more than
once for each activated object.
For example, from a quick look at the code (GenericObjectPool.java, v1.5.4),
it would be possible to do the following:
1) Create a pool with 10 objects.
2) Borrow all 10 objects from the pool.
3) Call getNumActive (returns 10).
4) Call invalidateObject for ONE of the objects 11 times.
5) Call getNumActive (returns -1).
The invalidateObject method calls the _factory to destroy the object, and
subsequent calls to destroy the same object may or may not result in an
exception. Regardless, _numActive is decremented within a finally block, and
therefore would always be decremented even if the object had already been
invalidated and destroyed.
I'd like to suggest using a HashSet instead of a counter to keep track of
active objects. If borrowing an object added it to a HashSet, and returning
or invaliding the object removed it from the HashSet (subsequent removes
would be no-ops), the example given above would not result in an incorrect
value when getNumActive is called (it would just return the current size of
the HashSet).
Note that although unrelated to this bug, it might also be wise to use a
HashSet instead of the int counter _numInternalProcessing.
--
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