Multi-threading bug in XmlScanner/FixedNsContext

[bcoughlan]

I believe that there is a multi-threading bug in XmlScanner/FixedNsContext.

I suspect that this is because XmlScanner uses the static FixedNsContext.EMPTY_CONTEXT initially, so threads are sharing the _tmpDecl array in FixedNsContext.

I am not familiar enough with Aalto to produce a fix, but I did manage to create a reproducible example (you may need to run it a few times to get the error):

package performance;

import com.fasterxml.aalto.AsyncByteBufferFeeder;
import com.fasterxml.aalto.AsyncXMLInputFactory;
import com.fasterxml.aalto.AsyncXMLStreamReader;
import com.fasterxml.aalto.evt.EventAllocatorImpl;
import com.fasterxml.aalto.stax.InputFactoryImpl;

import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

import javax.xml.stream.util.XMLEventAllocator;

public class AaltoBug implements Runnable {

    private static String xml = "<?xml version='1.0'?><stream:stream xmlns='jabber:client' xmlns:stream='http://etherx.jabber.org/streams' id='4095288169' from='localhost' version='1.0' xml:lang='en'>";
    private static int NUM_THREADS = 5;
    private static XMLEventAllocator allocator = EventAllocatorImpl.getDefaultInstance();
    private static AsyncXMLInputFactory inputFactory = new InputFactoryImpl();

    public static void main(String[] args) throws InterruptedException {
        ExecutorService ex = Executors.newFixedThreadPool(NUM_THREADS);

        for (int i = 0; i < 100000; i++) {
            ex.submit(new AaltoBug(i));
        }

        ex.shutdown();
        ex.awaitTermination(Integer.MAX_VALUE, TimeUnit.SECONDS);
    }

    private final int count;

    public AaltoBug(int count) {
        this.count = count;
    }

    @Override
    public void run() {
        try {
            ByteBuffer bb = StandardCharsets.UTF_8.encode(xml);
            AsyncXMLStreamReader<AsyncByteBufferFeeder> parser = inputFactory.createAsyncForByteBuffer();
            parser.getInputFeeder().feedInput(bb);
            while (parser.hasNext()) {
                int eventType = parser.next();
                if (eventType == AsyncXMLStreamReader.EVENT_INCOMPLETE) {
                    break;
                }

                allocator.allocate(parser);
            }
        } catch (Exception e) {
            System.out.println("Error in " + count);
            e.printStackTrace();
        }
    }
}

Which produces this exception:

java.lang.ArrayIndexOutOfBoundsException: 10
    at java.util.ArrayList.add(ArrayList.java:459)
    at com.fasterxml.aalto.in.FixedNsContext.reuseOrCreate(FixedNsContext.java:76)
    at com.fasterxml.aalto.in.XmlScanner.getNonTransientNamespaceContext(XmlScanner.java:916)
    at com.fasterxml.aalto.stax.StreamReaderImpl.getNonTransientNamespaceContext(StreamReaderImpl.java:1528)
    at org.codehaus.stax2.ri.evt.Stax2EventAllocatorImpl.createStartElement(Stax2EventAllocatorImpl.java:160)
    at org.codehaus.stax2.ri.evt.Stax2EventAllocatorImpl.allocate(Stax2EventAllocatorImpl.java:69)
    at com.fasterxml.aalto.evt.EventAllocatorImpl.allocate(EventAllocatorImpl.java:103)
    at performance.AaltoBug.run(AaltoBug.java:61)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)

[cowtowncoder]

First of all, thank you for reporting this and providing reproduction. Second all, sorry for the delay in addressing it.
But for what it is worth, I fixed this and it will be included in 1.0.0, due to release soon.