Re: RMI Serializing Error

FYI

This is a known bug in the Sun JVM (pre 1.5)

See bug 4888942
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4888942

// Mattias

Jason Sicotte wrote:
> By "calling thread" I meant an arbitrary thread that has a reference to the
> HashMap.
>
> The Collections.synchronizedMap() call can be thought of as taking all the
> methods and putting synchronized(this){} blocks in them.  The exemptions for
> this rule are writeObject() and readObject().  These methods are private
> HashMap methods and their behaviour can not be changed by synchronizedMap().
>
> So there are two solutions to the problem: use clone() or extend/wrap the
> HashMap making sure to implement your own writeObject() and readObject()
> methods.  Most, if not all the methods in the second solution must have
> synchronization blocks which lock on "this" to block any external access.
> The especially important methods are put() and the aforementioned
> serialization methods.
>
> I am currently using clone() to return a copy of the HashMap so that the Web
> UI does not fall over at random.  After running some JMeter tests, it turns
> out that the UI requests are on average 30ms longer (for HashMaps containing
> 400 our objects).  This small protraction in time is not human noticeable
> which is acceptable.  And of course, this is not a universal benchmark and
> your mileage may vary.
>
> Thank you for your time,
> Jason
>
> On Thu, 30 Dec 2004 11:06:49 +0800, Niclas Hedhman <[email protected]> wrote:
>
>
>>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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For a list of frequently asked RMI questions please refer to:
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To view past RMI-USERS postings, please see:
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