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Posted to dev@activemq.apache.org by "Bryan Schmidt (JIRA)" <ji...@apache.org> on 2006/09/19 21:42:27 UTC
[jira] Created: (AMQ-930) Session 'consumers' hashtable susceptible
to invalid operation exception
Session 'consumers' hashtable susceptible to invalid operation exception
------------------------------------------------------------------------
Key: AMQ-930
URL: https://issues.apache.org/activemq/browse/AMQ-930
Project: ActiveMQ
Issue Type: Bug
Components: NMS (C# client)
Affects Versions: incubation
Environment: Windows XP, NMS API running against a AMQ 4.0.2 provider
Reporter: Bryan Schmidt
In a multithreaded environment that reuses the Session object, the following exception is thrown:
Invalid operation exception with the text: "Collection was modified; enumeration operation may not execute."
The exception is thrown when iterating through Session's consumers.Values collection. It appears that the lock is being ignored. Spinning up a new thread fixes the problem:
--- Session.cs, DispatchAsyncMessages method ---
public void DispatchAsyncMessages(object state)
{
// lets iterate through each consumer created by this session
// ensuring that they have all pending messages dispatched
lock (this)
{
// lets ensure that only 1 thread dispatches messages in a consumer at once
foreach (MessageConsumer consumer in consumers.Values)
{
ThreadPool.QueueUserWorkItem(new WaitCallback(consumer.DispatchAsyncMessages));
}
}
}
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[jira] Commented: (AMQ-930) Session 'consumers' hashtable
susceptible to invalid operation exception
Posted by "james strachan (JIRA)" <ji...@apache.org>.
[ https://issues.apache.org/activemq/browse/AMQ-930?page=comments#action_36991 ]
james strachan commented on AMQ-930:
------------------------------------
I don't quite understand the reason for this patch - I wonder if you could help explain it?
Session.DispatchAsyncMessages() is only ever called in a separate thread pool via a call to ThreadPool.QueueUserWorkItem(new WaitCallback(session.DispatchAsyncMessages) in the MessageConsumer.
The idea is that only 1 thread at once calls this method for all consumers created by the session. (In NMS, just like in JMS, messages are only dispatched from one session at once to however many consumers it has - rather than dispatching to multiple consumers in parallel).
Am wondering if a better fix is just to ensure that the collection ("consumer.Values") is completely thread safe to avoid the concurrent modification errors you are seeing. I'm working on a patch right now - will commit it shortly - am wondering if this is a better approach?
> Session 'consumers' hashtable susceptible to invalid operation exception
> ------------------------------------------------------------------------
>
> Key: AMQ-930
> URL: https://issues.apache.org/activemq/browse/AMQ-930
> Project: ActiveMQ
> Issue Type: Bug
> Components: NMS (C# client)
> Affects Versions: incubation
> Environment: Windows XP, NMS API running against a AMQ 4.0.2 provider
> Reporter: Bryan Schmidt
>
> In a multithreaded environment that reuses the Session object, the following exception is thrown:
> Invalid operation exception with the text: "Collection was modified; enumeration operation may not execute."
> The exception is thrown when iterating through Session's consumers.Values collection. It appears that the lock is being ignored. Spinning up a new thread fixes the problem:
> --- Session.cs, DispatchAsyncMessages method ---
> public void DispatchAsyncMessages(object state)
> {
> // lets iterate through each consumer created by this session
> // ensuring that they have all pending messages dispatched
> lock (this)
> {
> // lets ensure that only 1 thread dispatches messages in a consumer at once
> foreach (MessageConsumer consumer in consumers.Values)
> {
> ThreadPool.QueueUserWorkItem(new WaitCallback(consumer.DispatchAsyncMessages));
> }
> }
> }
--
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[jira] Commented: (AMQ-930) Session 'consumers' hashtable
susceptible to invalid operation exception
Posted by "Bryan Schmidt (JIRA)" <ji...@apache.org>.
[ https://issues.apache.org/activemq/browse/AMQ-930?page=comments#action_36998 ]
Bryan Schmidt commented on AMQ-930:
-----------------------------------
Your solution looks good. Thanks!
> Session 'consumers' hashtable susceptible to invalid operation exception
> ------------------------------------------------------------------------
>
> Key: AMQ-930
> URL: https://issues.apache.org/activemq/browse/AMQ-930
> Project: ActiveMQ
> Issue Type: Bug
> Components: NMS (C# client)
> Affects Versions: incubation
> Environment: Windows XP, NMS API running against a AMQ 4.0.2 provider
> Reporter: Bryan Schmidt
>
> In a multithreaded environment that reuses the Session object, the following exception is thrown:
> Invalid operation exception with the text: "Collection was modified; enumeration operation may not execute."
> The exception is thrown when iterating through Session's consumers.Values collection. It appears that the lock is being ignored. Spinning up a new thread fixes the problem:
> --- Session.cs, DispatchAsyncMessages method ---
> public void DispatchAsyncMessages(object state)
> {
> // lets iterate through each consumer created by this session
> // ensuring that they have all pending messages dispatched
> lock (this)
> {
> // lets ensure that only 1 thread dispatches messages in a consumer at once
> foreach (MessageConsumer consumer in consumers.Values)
> {
> ThreadPool.QueueUserWorkItem(new WaitCallback(consumer.DispatchAsyncMessages));
> }
> }
> }
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[jira] Resolved: (AMQ-930) Session 'consumers' hashtable
susceptible to invalid operation exception
Posted by "james strachan (JIRA)" <ji...@apache.org>.
[ https://issues.apache.org/activemq/browse/AMQ-930?page=all ]
james strachan resolved AMQ-930.
--------------------------------
Fix Version/s: 4.1
Resolution: Fixed
Patch applied to ensure consumers.Values is thread safe to fix the issue
> Session 'consumers' hashtable susceptible to invalid operation exception
> ------------------------------------------------------------------------
>
> Key: AMQ-930
> URL: https://issues.apache.org/activemq/browse/AMQ-930
> Project: ActiveMQ
> Issue Type: Bug
> Components: NMS (C# client)
> Affects Versions: incubation
> Environment: Windows XP, NMS API running against a AMQ 4.0.2 provider
> Reporter: Bryan Schmidt
> Fix For: 4.1
>
>
> In a multithreaded environment that reuses the Session object, the following exception is thrown:
> Invalid operation exception with the text: "Collection was modified; enumeration operation may not execute."
> The exception is thrown when iterating through Session's consumers.Values collection. It appears that the lock is being ignored. Spinning up a new thread fixes the problem:
> --- Session.cs, DispatchAsyncMessages method ---
> public void DispatchAsyncMessages(object state)
> {
> // lets iterate through each consumer created by this session
> // ensuring that they have all pending messages dispatched
> lock (this)
> {
> // lets ensure that only 1 thread dispatches messages in a consumer at once
> foreach (MessageConsumer consumer in consumers.Values)
> {
> ThreadPool.QueueUserWorkItem(new WaitCallback(consumer.DispatchAsyncMessages));
> }
> }
> }
--
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