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From "Jim Gomes (JIRA)" <jira+amq...@apache.org>
Subject [jira] Work logged: (AMQNET-112) Threading issues -- Insufficient synchronization in Connection, Session, etc.
Date Tue, 09 Sep 2008 17:13:52 GMT

     [ https://issues.apache.org/activemq/browse/AMQNET-112?page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#action_36777
]

Jim Gomes logged work on AMQNET-112:
------------------------------------

                Author: Jim Gomes
            Created on: 09/Sep/08 10:13 AM
            Start Date: 09/Sep/08 10:12 AM
    Worklog Time Spent: 1 hour 
      Work Description: Merge patch and review changes.

Issue Time Tracking
-------------------

    Remaining Estimate: 0 minutes
            Time Spent: 1 hour

> Threading issues -- Insufficient synchronization in Connection, Session, etc.
> -----------------------------------------------------------------------------
>
>                 Key: AMQNET-112
>                 URL: https://issues.apache.org/activemq/browse/AMQNET-112
>             Project: ActiveMQ .Net
>          Issue Type: Bug
>          Components: ActiveMQ Client
>    Affects Versions: 1.0
>            Reporter: Chris Fraire
>            Assignee: Jim Gomes
>             Fix For: 1.1
>
>         Attachments: Apache.NMS.ActiveMQ.patch
>
>          Time Spent: 1 hour
>  Remaining Estimate: 0 minutes
>
> I have been debugging some threading issues in NMS, and I have attached a patch file
with some proposed changes to correct the following issues:
> * Some threading issues in Connection, Session, and DispatchingThread
> - it is insufficient to use ArrayList.Synchronized or Hashtable.Synchronized since enumeration
is not synchronized.  Instead, use regular collections and explicit locking using a private
object, myLock
> - instead of Connection.connected, use a volatile single-state-change bool called triedConnect,
to add synchronization to CheckConnected without adversely-affecting performance 
> - mark as volatile certain bools which have a single state change (e.g., Connection.closed,
which starts at false and changes once to true) and then double-check for minimal locking
> - some uses of AtomicBoolean (e.g., Connection.started) offered insufficient code synchronization.
 Instead, use regular bool and locking of the aforementioned myLock
> - remove Connection.closing field, and instead always accommodate that Connection.RemoveSession
modifies the sessions list.
> - instead of (bool) DispatchingThread.m_bStopFlag, use a ManualResetEvent (in addition
to the existing AutoResetEvent) to signal the worker thread
> - in TcpTransport, recognize that ShutdownCommand may cause broker to close connection,
to avoid a spurious error message
> - accommodate potential ThreadAbortExceptions which can occur from explicitly-aborted
worker threads
> - increase the wait for stopping async delivery, from 5 seconds to 30
> - use Interlocked.Increment for thread-safe int increments.  (Interlocked.Increment wraps
Int32.MaxValue to Int32.MinValue; will this be a problem?)
> * Tweak implementation of IDisposeable in TcpTransport, MutexTransport, TransportFilter,
WireFormatNegotiator so finalizers call Dispose
> Thank you,
> Chris

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