Re: RMI Serializing Error

On Thursday 30 December 2004 02:47, Jason Sicotte wrote:

> Seeming as you, (and I am certain others on the list) are more
> knowledgeable than I on the subject of threads, let me sate my question as
> this:  How can I modify the application outlined in
>
> http://archives.java.sun.com/cgi-bin/wa?A2=ind0412&L=rmi-users&F=&S=&P=3197
>
> to lock access to a HashMap reference from an external thread after that
> thread has already obtained a reference?  This must be done without
> modification to the calling thread.

Sorry, the question doesn't really compute for me. "Calling Thread" is what?
All threads of interest are calling the the HashMap. (Also, *must not* is
pretty strong words, as there are cases when there is no way around fixing
other people's broken systems.)

I have never really understood what Collections.synchronizedMap() does, and
never use it. If you want to complain about thread safety in the JDK, it is
probably here the complaint should go.

Never the less;

Instead, I would either subclass HashMap, or (more likely) implement my own
Map which delegates to an underlying HashMap, which are thread safe. Making
it thread safe can be done in a few ways, where synchronized methods are the
most obvious, but could become a bottle neck. Cloning may not be as bad as
you think from a performance point of view. It depends a lot on the
application type, such as how large is the HashMap and how often is it
updated (I assume that the code you give is just exemplifying the real
problem).

This can be done without modifying the RMI client ( I assume that is what you
mean by the "calling thread"), but the server must be modified.

Cheers
Niclas
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