Threading issues -- Insufficient synchronization in Connection, Session, etc.
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Key: AMQNET-112
URL: https://issues.apache.org/activemq/browse/AMQNET-112
Project: ActiveMQ .Net
Issue Type: Bug
Components: ActiveMQ Client
Reporter: Chris Fraire
Assignee: James Strachan
Attachments: Apache.NMS.ActiveMQ.patch
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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