Hi,

Deadlock occurs, while running a very simple test, which is just trying to checkout/checkin node within transaction concurrently from 2 threads.

Find enclosed thread dump, log and simple Java program.
I'm using UserTransaction implementation from jackrabbit test suite.

Regards
Przemo Pakulski
www.cognifide.com
Full thread dump Java HotSpot(TM) Client VM (1.4.2_08-b03 mixed mode):

"Thread-5" prio=5 tid=0x03054c48 nid=0x180c in Object.wait() [355f000..355fd8c]
        at java.lang.Object.wait(Native Method)
        - waiting on <0x1148ef20> (a 
EDU.oswego.cs.dl.util.concurrent.WriterPreferenceReadWriteLock$WriterLock)
        at java.lang.Object.wait(Object.java:429)
        at 
EDU.oswego.cs.dl.util.concurrent.WriterPreferenceReadWriteLock$WriterLock.acquire(Unknown
 Source)
        - locked <0x1148ef20> (a 
EDU.oswego.cs.dl.util.concurrent.WriterPreferenceReadWriteLock$WriterLock)
        at 
org.apache.jackrabbit.core.state.SharedItemStateManager.acquireWriteLock(SharedItemStateManager.java:1137)
        at 
org.apache.jackrabbit.core.state.SharedItemStateManager.access$200(SharedItemStateManager.java:110)
        at 
org.apache.jackrabbit.core.state.SharedItemStateManager$Update.begin(SharedItemStateManager.java:456)
        at 
org.apache.jackrabbit.core.state.SharedItemStateManager.beginUpdate(SharedItemStateManager.java:651)
        at 
org.apache.jackrabbit.core.state.XAItemStateManager.prepare(XAItemStateManager.java:150)
        at 
org.apache.jackrabbit.core.TransactionContext.prepare(TransactionContext.java:128)
        - locked <0x11565ac8> (a org.apache.jackrabbit.core.TransactionContext)
        at 
org.apache.jackrabbit.core.XASessionImpl.prepare(XASessionImpl.java:300)
        at 
com.oyster.mom.contentserver.jcr.transaction.JackrabbitUserTransaction.commit(JackrabbitUserTransaction.java:102)
        at 
com.oyster.mom.contentserver.jcr.transaction.JrTestDeadlock.run(JrTestDeadlock.java:97)

"Thread-4" prio=5 tid=0x0303b348 nid=0x9d0 in Object.wait() [351f000..351fd8c]
        at java.lang.Object.wait(Native Method)
        - waiting on <0x1148ef20> (a 
EDU.oswego.cs.dl.util.concurrent.WriterPreferenceReadWriteLock$WriterLock)
        at java.lang.Object.wait(Object.java:429)
        at 
EDU.oswego.cs.dl.util.concurrent.WriterPreferenceReadWriteLock$WriterLock.acquire(Unknown
 Source)
        - locked <0x1148ef20> (a 
EDU.oswego.cs.dl.util.concurrent.WriterPreferenceReadWriteLock$WriterLock)
        at 
org.apache.jackrabbit.core.state.SharedItemStateManager.acquireWriteLock(SharedItemStateManager.java:1137)
        at 
org.apache.jackrabbit.core.state.SharedItemStateManager.access$200(SharedItemStateManager.java:110)
        at 
org.apache.jackrabbit.core.state.SharedItemStateManager$Update.begin(SharedItemStateManager.java:456)
        at 
org.apache.jackrabbit.core.state.SharedItemStateManager.beginUpdate(SharedItemStateManager.java:651)
        at 
org.apache.jackrabbit.core.state.XAItemStateManager.prepare(XAItemStateManager.java:150)
        at 
org.apache.jackrabbit.core.TransactionContext.prepare(TransactionContext.java:128)
        - locked <0x1156f558> (a org.apache.jackrabbit.core.TransactionContext)
        at 
org.apache.jackrabbit.core.XASessionImpl.prepare(XASessionImpl.java:300)
        at 
com.oyster.mom.contentserver.jcr.transaction.JackrabbitUserTransaction.commit(JackrabbitUserTransaction.java:102)
        at 
com.oyster.mom.contentserver.jcr.transaction.JrTestDeadlock.run(JrTestDeadlock.java:97)

"IndexMerger" daemon prio=5 tid=0x030388b8 nid=0x1858 in Object.wait() 
[34df000..34dfd8c]
        at java.lang.Object.wait(Native Method)
        - waiting on <0x114fd280> (a 
org.apache.commons.collections.buffer.BlockingBuffer)
        at java.lang.Object.wait(Object.java:429)
        at 
org.apache.commons.collections.buffer.BlockingBuffer.remove(BlockingBuffer.java:107)
        - locked <0x114fd280> (a 
org.apache.commons.collections.buffer.BlockingBuffer)
        at 
org.apache.jackrabbit.core.query.lucene.IndexMerger.run(IndexMerger.java:235)

"Thread-2" daemon prio=5 tid=0x0303a230 nid=0xe4c in Object.wait() 
[349f000..349fd8c]
        at java.lang.Object.wait(Native Method)
        - waiting on <0x114fd2e0> (a java.util.TaskQueue)
        at java.util.TimerThread.mainLoop(Timer.java:429)
        - locked <0x114fd2e0> (a java.util.TaskQueue)
        at java.util.TimerThread.run(Timer.java:382)

"Thread-1" daemon prio=5 tid=0x0301b7a0 nid=0x1a00 in Object.wait() 
[345f000..345fd8c]
        at java.lang.Object.wait(Native Method)
        - waiting on <0x114f9058> (a java.util.TaskQueue)
        at java.lang.Object.wait(Object.java:429)
        at java.util.TimerThread.mainLoop(Timer.java:403)
        - locked <0x114f9058> (a java.util.TaskQueue)
        at java.util.TimerThread.run(Timer.java:382)

"ObservationManager" daemon prio=5 tid=0x02ef6c50 nid=0x10d8 in Object.wait() 
[341f000..341fd8c]
        at java.lang.Object.wait(Native Method)
        - waiting on <0x114f38e0> (a 
org.apache.commons.collections.buffer.BlockingBuffer)
        at java.lang.Object.wait(Object.java:429)
        at 
org.apache.commons.collections.buffer.BlockingBuffer.remove(BlockingBuffer.java:107)
        - locked <0x114f38e0> (a 
org.apache.commons.collections.buffer.BlockingBuffer)
        at 
org.apache.jackrabbit.core.observation.ObservationManagerFactory.run(ObservationManagerFactory.java:155)
        at java.lang.Thread.run(Thread.java:534)

"Signal Dispatcher" daemon prio=10 tid=0x00a05590 nid=0x1914 waiting on 
condition [0..0]

"Finalizer" daemon prio=9 tid=0x00a027f8 nid=0x17a4 in Object.wait() 
[2c9f000..2c9fd8c]
        at java.lang.Object.wait(Native Method)
        - waiting on <0x113db118> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:111)
        - locked <0x113db118> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:127)
        at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:159)

"Reference Handler" daemon prio=10 tid=0x00a01478 nid=0x16d4 in Object.wait() 
[2c5f000..2c5fd8c]
        at java.lang.Object.wait(Native Method)
        - waiting on <0x113db180> (a java.lang.ref.Reference$Lock)
        at java.lang.Object.wait(Object.java:429)
        at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:115)
        - locked <0x113db180> (a java.lang.ref.Reference$Lock)

"main" prio=5 tid=0x0003e6f0 nid=0x1470 in Object.wait() [7f000..7fc38]
        at java.lang.Object.wait(Native Method)
        - waiting on <0x11524f10> (a 
com.oyster.mom.contentserver.jcr.transaction.JrTestDeadlock)
        at java.lang.Thread.join(Thread.java:1001)
        - locked <0x11524f10> (a 
com.oyster.mom.contentserver.jcr.transaction.JrTestDeadlock)
        at java.lang.Thread.join(Thread.java:1054)
        at 
com.oyster.mom.contentserver.jcr.transaction.JrTestDeadlock.main(JrTestDeadlock.java:33)

"VM Thread" prio=5 tid=0x00a42730 nid=0x17d0 runnable

"VM Periodic Task Thread" prio=10 tid=0x00a45540 nid=0x1928 waiting on condition
"Suspend Checker Thread" prio=10 tid=0x00a04af8 nid=0x17ac runnable
import javax.jcr.Node;
import javax.jcr.RepositoryException;
import javax.jcr.Session;
import javax.jcr.SimpleCredentials;

import org.apache.jackrabbit.core.RepositoryImpl;
import org.apache.jackrabbit.core.config.RepositoryConfig;

public class JrTestDeadlock extends Thread {

    private static final org.apache.commons.logging.Log log = 
org.apache.commons.logging.LogFactory.getLog(JrTestDeadlock.class);

    public static String REPOSITORY_HOME = "d:/repo/jackrabbit/";

    public static String REPOSITORY_CONFIG = REPOSITORY_HOME + "repository.xml";

    public static void main(String[] args) throws Exception {

        JrTestDeadlock test = new JrTestDeadlock(-1);
        test.startup();

        JrTestDeadlock tests[] = new JrTestDeadlock[2];

        for (int i = 0; i < tests.length; i++) {
            JrTestDeadlock x = new JrTestDeadlock(i);
            x.start();
            tests[i] = x;
        }

        for (int i = 0; i < tests.length; i++) {
            tests[i].join();
        }

        test.shutdown();
    }

    private static RepositoryImpl repository;

    private int id;

    public JrTestDeadlock(int i) {
        this.id = i;
    }

    public void startup() throws Exception {
        System.setProperty("java.security.auth.login.config", "c:/jaas.config");

        RepositoryConfig config = RepositoryConfig.create(REPOSITORY_CONFIG, 
REPOSITORY_HOME);
        repository = RepositoryImpl.create(config);

        Session session = repository.login(new SimpleCredentials("admin", 
"admin".toCharArray()));
        Node rootNode = session.getRootNode();
        if (!rootNode.hasNode("folder")) {
            Node folder = rootNode.addNode("folder");
            folder.addMixin("mix:versionable");
            folder.addMixin("mix:lockable");
            rootNode.save();
        }
        session.logout();
    }

    public void shutdown() throws RepositoryException {
        repository.shutdown();
    }

    public Node getFolder(Session session) throws RepositoryException {
        return session.getRootNode().getNode("folder");
    }

    public void run() {
        try {
            Session session = repository.login(new SimpleCredentials("admin", 
"admin".toCharArray()));
            for (int i = 0; i < 100; i++) {
                log.error("START id:" + id + ", i=" + i);

                boolean success = false;

                JackrabbitUserTransaction ut = new 
JackrabbitUserTransaction(session);
                try {
                    ut.begin();

                    Node folder = getFolder(session);
                    folder.checkout();
                    folder.checkin();

                    success = true;
                    log.info("SUCCESS id:" + id + ", i=" + i);
                }
                catch (Exception e) {
                    log.warn("FAIL:" + id + ", i=" + i, e);
                }
                finally {
                    try {
                        if (success) {
                            ut.commit();
                        }
                        else {
                            ut.rollback();
                        }
                    }
                    catch (Exception e) {
                        log.fatal(e);
                    }
                }
            }
            session.logout();
        }
        catch (RepositoryException e) {
            e.printStackTrace();
        }
    }
}
13:46 ERROR JrTestDeadlock.run(JrTestDeadlock.java:76) - START id:0, i=0
13:46 ERROR JrTestDeadlock.run(JrTestDeadlock.java:76) - START id:1, i=0
13:46 INFO  JrTestDeadlock.run(JrTestDeadlock.java:89) - SUCCESS id:0, i=0
13:46 INFO  JrTestDeadlock.run(JrTestDeadlock.java:89) - SUCCESS id:1, i=0
13:46 ERROR 
org.apache.jackrabbit.core.state.XAItemStateManager.prepare(XAItemStateManager.java:156)
 - org.apache.jackrabbit.core.state.StaleItemStateException: 
233e656f-79f8-414d-9e37-3fce865b492d/{http://www.jcp.org/jcr/1.0}isCheckedOut 
has been modified externally
13:46 FATAL JrTestDeadlock.run(JrTestDeadlock.java:104) - 
javax.transaction.RollbackException: Transaction rolled back: XA_ERR=104
13:46 ERROR JrTestDeadlock.run(JrTestDeadlock.java:76) - START id:1, i=1
13:46 WARN  JrTestDeadlock.run(JrTestDeadlock.java:92) - FAIL:1, i=1
ax.jcr.InvalidItemStateException: f83a830b-abbf-4ab2-8625-b9e2c4802316: the 
item does not exist anymore
     at 
org.apache.jackrabbit.core.version.XAVersion.sanityCheck(XAVersion.java:81)
     at 
org.apache.jackrabbit.core.version.XAVersion.getInternalVersion(XAVersion.java:70)
     at 
org.apache.jackrabbit.core.version.AbstractVersion.getUUID(AbstractVersion.java:107)
     at org.apache.jackrabbit.core.NodeImpl.checkout(NodeImpl.java:2759)
     at JrTestDeadlock.run(JrTestDeadlock.java:85)
13:46 ERROR JrTestDeadlock.run(JrTestDeadlock.java:76) - START id:1, i=2
13:46 INFO  JrTestDeadlock.run(JrTestDeadlock.java:89) - SUCCESS id:1, i=2
13:51 WARN  
org.apache.jackrabbit.core.TransactionContext.run(TransactionContext.java:239) 
- Transaction rolled back because timeout expired.
        

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