Session can deadlock on responderSync and reduced concurrency

Because Session is using a String literal as a lock, the scope of this lock is not per Session instance

private String responderSync = "SessionResponderSync";
// @GuardedBy(responderSync)
private Responder responder;

As well as reducing concurrency it caused my app to deadlock, because the vm will intern "SessionResponderSync". I suggest changing this to

private String responderSync = new String("SessionResponderSync");

My deadlock was probably caused because I was trying a combination of

1) synchronous writes on both the acceptor and initiator
2) both the acceptor and initiator in the same vm process
3) switching out the LinkedBlockingQueue in the SingleThreadedEventHandlingStrategy with a bounded ArrayBlockingQueue

Here is my stack trace if it helps:

SocketConnectorIoProcessor-0.0@1168 daemon, priority=5, in group 'main', status: 'WAIT'
at sun.misc.Unsafe.park(Unsafe.java:-1)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:158)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1,925)
at java.util.concurrent.ArrayBlockingQueue.put(ArrayBlockingQueue.java:252)
at quickfix.mina.SingleThreadedEventHandlingStrategy.onMessage(SingleThreadedEventHandlingStrategy.java:47)
at quickfix.mina.initiator.InitiatorIoHandler.processMessage(InitiatorIoHandler.java:54)
at quickfix.mina.AbstractIoHandler.messageReceived(AbstractIoHandler.java:113)
at org.apache.mina.common.support.AbstractIoFilterChain$TailFilter.messageReceived(AbstractIoFilterChain.java:570)
at org.apache.mina.common.support.AbstractIoFilterChain.callNextMessageReceived(AbstractIoFilterChain.java:299)
at org.apache.mina.common.support.AbstractIoFilterChain.access$1100(AbstractIoFilterChain.java:53)
at org.apache.mina.common.support.AbstractIoFilterChain$EntryImpl$1.messageReceived(AbstractIoFilterChain.java:648)
at org.apache.mina.filter.codec.support.SimpleProtocolDecoderOutput.flush(SimpleProtocolDecoderOutput.java:58)
at org.apache.mina.filter.codec.ProtocolCodecFilter.messageReceived(ProtocolCodecFilter.java:180)
at org.apache.mina.common.support.AbstractIoFilterChain.callNextMessageReceived(AbstractIoFilterChain.java:299)
at org.apache.mina.common.support.AbstractIoFilterChain.access$1100(AbstractIoFilterChain.java:53)
at org.apache.mina.common.support.AbstractIoFilterChain$EntryImpl$1.messageReceived(AbstractIoFilterChain.java:648)
at org.apache.mina.common.support.AbstractIoFilterChain$HeadFilter.messageReceived(AbstractIoFilterChain.java:499)
at org.apache.mina.common.support.AbstractIoFilterChain.callNextMessageReceived(AbstractIoFilterChain.java:299)
at org.apache.mina.common.support.AbstractIoFilterChain.fireMessageReceived(AbstractIoFilterChain.java:293)
at org.apache.mina.transport.socket.nio.SocketIoProcessor.read(SocketIoProcessor.java:228)
at org.apache.mina.transport.socket.nio.SocketIoProcessor.process(SocketIoProcessor.java:198)
at org.apache.mina.transport.socket.nio.SocketIoProcessor.access$400(SocketIoProcessor.java:45)
at org.apache.mina.transport.socket.nio.SocketIoProcessor$Worker.run(SocketIoProcessor.java:485)
at org.apache.mina.util.NamePreservingRunnable.run(NamePreservingRunnable.java:51)
at java.lang.Thread.run(Thread.java:619)

SocketAcceptorIoProcessor-0.0@1170, priority=5, in group 'main', status: 'WAIT'
at sun.misc.Unsafe.park(Unsafe.java:-1)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:158)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1,925)
at java.util.concurrent.ArrayBlockingQueue.put(ArrayBlockingQueue.java:252)
at quickfix.mina.SingleThreadedEventHandlingStrategy.onMessage(SingleThreadedEventHandlingStrategy.java:47)
at quickfix.mina.acceptor.AcceptorIoHandler.processMessage(AcceptorIoHandler.java:97)
at quickfix.mina.AbstractIoHandler.messageReceived(AbstractIoHandler.java:113)
at org.apache.mina.common.support.AbstractIoFilterChain$TailFilter.messageReceived(AbstractIoFilterChain.java:570)
at org.apache.mina.common.support.AbstractIoFilterChain.callNextMessageReceived(AbstractIoFilterChain.java:299)
at org.apache.mina.common.support.AbstractIoFilterChain.access$1100(AbstractIoFilterChain.java:53)
at org.apache.mina.common.support.AbstractIoFilterChain$EntryImpl$1.messageReceived(AbstractIoFilterChain.java:648)
at org.apache.mina.filter.codec.support.SimpleProtocolDecoderOutput.flush(SimpleProtocolDecoderOutput.java:58)
at org.apache.mina.filter.codec.ProtocolCodecFilter.messageReceived(ProtocolCodecFilter.java:180)
at org.apache.mina.common.support.AbstractIoFilterChain.callNextMessageReceived(AbstractIoFilterChain.java:299)
at org.apache.mina.common.support.AbstractIoFilterChain.access$1100(AbstractIoFilterChain.java:53)
at org.apache.mina.common.support.AbstractIoFilterChain$EntryImpl$1.messageReceived(AbstractIoFilterChain.java:648)
at org.apache.mina.common.support.AbstractIoFilterChain$HeadFilter.messageReceived(AbstractIoFilterChain.java:499)
at org.apache.mina.common.support.AbstractIoFilterChain.callNextMessageReceived(AbstractIoFilterChain.java:299)
at org.apache.mina.common.support.AbstractIoFilterChain.fireMessageReceived(AbstractIoFilterChain.java:293)
at org.apache.mina.transport.socket.nio.SocketIoProcessor.read(SocketIoProcessor.java:228)
at org.apache.mina.transport.socket.nio.SocketIoProcessor.process(SocketIoProcessor.java:198)
at org.apache.mina.transport.socket.nio.SocketIoProcessor.access$400(SocketIoProcessor.java:45)
at org.apache.mina.transport.socket.nio.SocketIoProcessor$Worker.run(SocketIoProcessor.java:485)
at org.apache.mina.util.NamePreservingRunnable.run(NamePreservingRunnable.java:51)
at java.lang.Thread.run(Thread.java:619)

SocketConnector-0@1154 daemon, priority=5, in group 'main', status: 'RUNNING'
at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(WindowsSelectorImpl.java:-1)
at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll(WindowsSelectorImpl.java:274)
at sun.nio.ch.WindowsSelectorImpl$SubSelector.access$400(WindowsSelectorImpl.java:256)
at sun.nio.ch.WindowsSelectorImpl.doSelect(WindowsSelectorImpl.java:137)
at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:69)
at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:80)
at org.apache.mina.transport.socket.nio.SocketConnector$Worker.run(SocketConnector.java:378)
at org.apache.mina.util.NamePreservingRunnable.run(NamePreservingRunnable.java:51)
at java.lang.Thread.run(Thread.java:619)

QFJ Message Processor@1284 daemon, priority=5, in group 'main', status: 'MONITOR'
waiting for main@1
at quickfix.Session.getResponder(Session.java:382)
at quickfix.Session.hasResponder(Session.java:393)
at quickfix.Session.next(Session.java:1,417)
at quickfix.Session.next(Session.java:853)
at quickfix.mina.SingleThreadedEventHandlingStrategy$SessionMessageEvent.processMessage(SingleThreadedEventHandlingStrategy.java:107)
at quickfix.mina.SingleThreadedEventHandlingStrategy.block(SingleThreadedEventHandlingStrategy.java:70)
at quickfix.mina.SingleThreadedEventHandlingStrategy$1.run(SingleThreadedEventHandlingStrategy.java:87)
at java.lang.Thread.run(Thread.java:619)

QFJ Message Processor@1236 daemon, priority=5, in group 'main', status: 'MONITOR'
waiting for main@1
at quickfix.Session.getResponder(Session.java:382)
at quickfix.Session.hasResponder(Session.java:393)
at quickfix.Session.next(Session.java:1,417)
at quickfix.Session.next(Session.java:853)
at quickfix.mina.SingleThreadedEventHandlingStrategy$SessionMessageEvent.processMessage(SingleThreadedEventHandlingStrategy.java:107)
at quickfix.mina.SingleThreadedEventHandlingStrategy.block(SingleThreadedEventHandlingStrategy.java:70)
at quickfix.mina.SingleThreadedEventHandlingStrategy$1.run(SingleThreadedEventHandlingStrategy.java:87)
at java.lang.Thread.run(Thread.java:619)

SocketAcceptor-0@1105, priority=5, in group 'main', status: 'RUNNING'
at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(WindowsSelectorImpl.java:-1)
at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll(WindowsSelectorImpl.java:274)
at sun.nio.ch.WindowsSelectorImpl$SubSelector.access$400(WindowsSelectorImpl.java:256)
at sun.nio.ch.WindowsSelectorImpl.doSelect(WindowsSelectorImpl.java:137)
at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:69)
at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:80)
at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:84)
at org.apache.mina.transport.socket.nio.SocketAcceptor$Worker.run(SocketAcceptor.java:220)
at org.apache.mina.util.NamePreservingRunnable.run(NamePreservingRunnable.java:51)
at java.lang.Thread.run(Thread.java:619)

QFJ Timer@1141 daemon, priority=5, in group 'main', status: 'MONITOR'
waiting for main@1
at quickfix.Session.getResponder(Session.java:382)
at quickfix.Session.hasResponder(Session.java:393)
at quickfix.Session.next(Session.java:1,417)
at quickfix.mina.SessionConnector$SessionTimerTask.run(SessionConnector.java:248)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
at java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:317)
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:150)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$101(ScheduledThreadPoolExecutor.java:98)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.runPeriodic(ScheduledThreadPoolExecutor.java:181)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:205)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:619)

OrderBook-testExchange-EURUSD-work-1@733, priority=5, in group 'main', status: 'MONITOR'
waiting for main@1
at quickfix.Session.send(Session.java:1,856)
at quickfix.Session.sendRaw(Session.java:1,803)
at quickfix.Session.send(Session.java:1,850)
at quickfix.Session.sendToTarget(Session.java:504)
... my stack

main@1, priority=5, in group 'main', status: 'WAIT'
blocks QFJ Message Processor@1284
blocks QFJ Message Processor@1236
blocks QFJ Timer@1141
blocks OrderBook-testExchange-EURUSD-work-1@733
at java.lang.Object.wait(Object.java:-1)
at org.apache.mina.common.support.DefaultIoFuture.await0(DefaultIoFuture.java:121)
at org.apache.mina.common.support.DefaultIoFuture.awaitUninterruptibly(DefaultIoFuture.java:100)
at org.apache.mina.common.support.DefaultIoFuture.join(DefaultIoFuture.java:79)
at quickfix.mina.IoSessionResponder.send(IoSessionResponder.java:50)
at quickfix.Session.send(Session.java:1,861)
at quickfix.Session.sendRaw(Session.java:1,803)
at quickfix.Session.send(Session.java:1,850)
at quickfix.Session.sendToTarget(Session.java:504)
... my stack