[infinispan-dev] Using marshaller internally in MarshalledValue and Marshalling reentrancy

[Galder Zamarreno]

Hi,

I'm trying to move MarshalledValue to use an injected Marshaller rather 
than relying on standard serialization and this is causing me a small 
problem:

One of the trade offs when making JBoss Marshalling 
marshaller/unmarshaller a thread local in JBoss Marshaller is reentrancy.

When marshalling a MarshalledValue, we call start() on the marshaller 
and then we'd call marshallerValue.getRaw(). The most reasonable 
implementation using an injected marshaller would call:

raw = marshaller.objectToBuffer(instance).getBuf();

By calling oTB again, you're calling start on the marshaller below and 
since this is a thread local, this is exactly the same instance and you 
get issues.

I don't think JBoss Marshalling marshaller/unmarshaller are meant to be 
reentrant and this is not my intention.

A second option would be to simply create a new marshaller in 
MarshalledValue.getRaw() but this means some initialisation that 
involves reflection, so this is no good.

The third option, an my preferred one, would be to add a boolean 
parameter to Marshaller.startObjectOutput() called cached. Based on this 
parameter, you could either get the marshaller from the thread local or 
if false, get a new one from the factory. This would get around the 
issue and makes the API more flexible coping with reentrant marshalling 
while for the rest of cases, taking advantage of the performance gains 
from using thread locals. The code in marshallerValue.getRaw() would 
then look like this:

ExposedByteArrayOutputStream baos = new ExposedByteArrayOutputStream(128);
ObjectOutput out = marshaller.startObjectOutput(baos, false);
try {
   marshaller.objectToObjectStream(instance);
} finally {
   marshaller.finishObjectOutput(out);
}
raw = baos.getRawBuffer();

Of course, I would document this accordingly in the API so that cached 
is only set to false if reentrant marshalling could happen.

Thoughts?
-- 
Galder Zamarreño
Sr. Software Maintenance Engineer
JBoss, a division of Red Hat