mongodb allanbank async driver callback being called twice - mongodb

Question

I have a simple callback bound to a findAsync call. Every few requests I observe a failure even though the data in the database is static.
Some quick debugging shows that my callback is ALWAYS being called twice. The cases where my app fails are caused by a null MongoIterator<Document> being passed in to my callback. Of course I only expected a single callback when the data is ready (or if there was an exception).
Is this expected behavior? Is there something I can do to ensure my callback is only called once when the query is complete?
Here is the code snippet:
collection.findAsync(
[
callback: { MongoIterator<Document> v ->
List data = []
try {
while(v.hasNext()) {
data.add(docToJson(v.next()))
}
} finally {
if (v != null) v.close()
}
sendReply([ status: 'ok', data: data ])
},
exception: { Throwable t ->
sendReply([ status: 'error', message: t.message ])
}
] as Callback<MongoIterator<Document>>,
find
)
Here is the stack trace:
Unexpected MongoDB Connection closed: Auth(MongoDB(43026-->localhost/127.0.0.1:27017)). Will try to reconnect.
Reconnected to localhost/127.0.0.1:27017
Exception in thread "MongoDB 43026<--localhost/127.0.0.1:27017" java.lang.NullPointerException: Cannot invoke method hasNext() on null object
at org.codehaus.groovy.runtime.NullObject.invokeMethod(NullObject.java:77)
at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.call(PogoMetaClassSite.java:45)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:45)
at org.codehaus.groovy.runtime.callsite.NullCallSite.call(NullCallSite.java:32)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:45)
at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.call(PogoMetaClassSite.java:54)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:112)
at mongoAsync$_run_closure2_closure6.doCall(mongoAsync.groovy:126)
at sun.reflect.GeneratedMethodAccessor54.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:90)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:233)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:272)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:909)
at groovy.lang.Closure.call(Closure.java:411)
at org.codehaus.groovy.runtime.ConvertedMap.invokeCustom(ConvertedMap.java:50)
at org.codehaus.groovy.runtime.ConversionHandler.invoke(ConversionHandler.java:81)
at com.sun.proxy.$Proxy14.callback(Unknown Source)
at com.allanbank.mongodb.client.AbstractReplyCallback.handle(AbstractReplyCallback.java:82)
at com.allanbank.mongodb.client.AbstractValidatingReplyCallback.callback(AbstractValidatingReplyCallback.java:72)
at com.allanbank.mongodb.client.AbstractValidatingReplyCallback.callback(AbstractValidatingReplyCallback.java:33)
at com.allanbank.mongodb.connection.message.ReplyHandler.reply(ReplyHandler.java:77)
at com.allanbank.mongodb.connection.socket.SocketConnection.reply(SocketConnection.java:560)
at com.allanbank.mongodb.connection.socket.SocketConnection$ReceiveRunnable.receiveOne(SocketConnection.java:735)
at com.allanbank.mongodb.connection.socket.SocketConnection$ReceiveRunnable.run(SocketConnection.java:683)
at java.lang.Thread.run(Thread.java:722)

Answer 1

Thanks for the extra information.
I am pretty sure I found the bug.
There is a race between the callback/iterator for the query getting the name of the server handling the query (needed for the GetMore requests) and the receive of a reply. Not sure how it has not been seen by others.
There is a patched jar here: [redact]. Let me know if it solves the problem for you.
The 1.2.2 version is available with the fix: http://www.allanbank.com/mongodb-async-driver/download.html
Assuming it does, I will push this fix out as a 1.2.2 tomorrow.
Rob.
Edit: Add link to official version.