[jbosscache-dev] Re: Any reason not to use ExposedByteArrayOutputStream instead of ByteArrayOutputStream ?

[Manik Surtani]

On 4 Jul 2008, at 10:46, Bela Ban wrote:

>
>
> Manik Surtani wrote:
>> cc'ing JBC-dev.
>>
>> The stream looks good, except that getting the raw buffer would  
>> mean that the buffer returned would "almost certainly be longer  
>> than the data written to it" (quoted from Brian's excellent  
>> javadocs).  Bela, how would JGroups behave with this?  Would it  
>> attempt to stream the entire buffer, including uninitialized values?
>
> Yes, good point, this is not good !  You would have to return an  
> org.jgroups.util.Buffer which has the byte[] buffer but also offset  
> and length:
>
> public class Buffer {
>   private final byte[] buf;
>   private final int offset;
>   private final int length;
>
>   public Buffer(byte[] buf, int offset, int length) {
>       this.buf=buf;
>       this.offset=offset;
>       this.length=length;
>   }
>
>   public byte[] getBuf() {
>       return buf;
>   }
>
>   public int getOffset() {
>       return offset;
>   }
>
>   public int getLength() {
>       return length;
>   }
>
>   public Buffer copy() {
>       byte[] new_buf=buf != null? new byte[length] : null;
>       int new_length=new_buf != null? new_buf.length : 0;
>       if(new_buf != null)
>           System.arraycopy(buf, offset, new_buf, 0, length);
>       return new Buffer(new_buf, 0, new_length);
>   }
>
>   public String toString() {
>       StringBuilder sb=new StringBuilder();
>       sb.append(length).append(" bytes");
>       if(offset > 0)
>           sb.append(" (offset=").append(offset).append(")");
>       return sb.toString();
>   }
>
> }
>
>
> In addition, I would have to change Marshaller to use a Buffer :
> public interface Marshaller {
>       *Buffer* objectToByteBuffer(Object obj) throws Exception;
>       Object objectFromByteBuffer(*Buffer* buf) throws Exception;
>   }
>

But that would involve JGroups code calling Buffer.copy() again, which  
is the same as using a normal BAOS.  Just that it happens a bit later  
in the chain of events.

> This should have far-reaching consequences as I'm not aware of  
> anyone else but JBossCache to use Marshaller. Or maybe, to be on the  
> safe side, I could create a Marshaller2 so existing code doesn't  
> break (extending Marshaller)... http://jira.jboss.com/jira/browse/JGRP-796That 
>  should
>
>> Will need to see how this gets de-serialized as well.  Also, since  
>> all cacheloaders use the same marshaller, will need to see how they  
>> deal with this as well.  Any code that relies on buf.length may end  
>> up at best writing unnecessary data and at worst breaking when  
>> deserializing.
> That shouldn't be an issue because your JBC marshalling code creates  
> local variables, and doesn't reuse ByteArrayOutputStream instances

I wasn't talking about reusing stream instances, I was referring to  
the same problem you have above with JGroups is going to be  
encountered with every cache loader impl in that the byte[] retrieved  
may be larger than necessary and contain uninitialized values.

Cheers,
--
Manik Surtani
Lead, JBoss Cache
manik at jboss.org