My understanding of concurrent modifications is that I can receive an
InvalidItemStateException if I have a stale view of the repository when
my session is saved or my transaction is committed. However, I can get
other exceptions using the code below. Furthermore, I thought
Jackrabbit would allow concurrent child node additions to a single node
given the child node names were unique. So I wasn't even expecting an
InvalidItemStateException for the code below.
I understand that locking can prevent the InvalidItemStateException but
I'm using transactions and committing the transaction for the sole
purpose of exposing a lock is something I'd like to avoid at this time.
I'd like to just catch the InvalidItemStateException and alert the user
with a friendly message.
Why do I get the given exceptions for the given code? I can supply full
stacks if necessary; for now, just the class and error message are shown.
Jackrabbit 1.6.0:
* org.apache.jackrabbit.core.state.ItemStateException: there's already a
property state instance with id
243f6e39-7a3e-4d48-b051-9b4198a6a16b/{http://www.jcp.org/jcr/1.0}primaryType
* javax.jcr.InvalidItemStateException: Item cannot be saved because it
has been modified externally: node /
* javax.jcr.InvalidItemStateException: node /: the node cannot be saved
because it has been modified externally.
Jackrabbit 1.6.5:
* javax.jcr.InvalidItemStateException: node /: the node cannot be saved
because it has been modified externally.
* javax.jcr.InvalidItemStateException: Item cannot be saved because it
has been modified externally: node /
* org.apache.jackrabbit.core.state.ItemStateException: Child node entry
with id 04afd8db-6515-4997-ac4e-83f066e39f53 has been removed, but is
not present in the changelog
Jackrabbit 2.3.4:
* java.util.ConcurrentModificationException
at java.util.WeakHashMap$HashIterator.nextEntry(WeakHashMap.java:762)
at java.util.WeakHashMap$KeyIterator.next(WeakHashMap.java:795)
at
org.apache.jackrabbit.core.cache.CacheManager.logCacheStats(CacheManager.java:164)
package test;
import java.io.File;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import javax.jcr.Repository;
import javax.jcr.RepositoryException;
import javax.jcr.Session;
import javax.jcr.SimpleCredentials;
import org.apache.jackrabbit.core.TransientRepository;
public class JackrabbitTest {
public static void main(final String[] args) throws Exception {
File dir = File.createTempFile("jackrabbit-test", "");
dir.delete();
dir.mkdir();
System.out.println("created temporary directory: " +
dir.getAbsolutePath());
dir.deleteOnExit();
final Repository jcrRepo = new TransientRepository(dir);
final AtomicBoolean passed = new AtomicBoolean(true);
final AtomicInteger counter = new AtomicInteger(0);
ExecutorService executor = Executors.newFixedThreadPool(50);
Runnable runnable = new Runnable() {
@Override
public void run() {
try {
Session session = jcrRepo.login(
new SimpleCredentials("admin",
"admin".toCharArray()));
session.getRootNode().addNode("n" +
counter.getAndIncrement()); //unique name
session.save();
session.logout();
} catch (RepositoryException e) {
e.printStackTrace();
passed.set(false);
}
}
};
System.out.println("Running threads");
for (int i = 0; i < 500; i++) {
executor.execute(runnable);
}
executor.shutdown(); //Disable new tasks from being submitted
if (!executor.awaitTermination(120, TimeUnit.SECONDS)) {
System.err.println("timeout");
System.exit(1);
}
if (!passed.get()) {
System.err.println("one or more threads got an exception");
System.exit(1);
} else {
System.out.println("all threads ran with no exceptions");
System.exit(0);
}
}
}
