Question about updating elements in an IList

[Richard O. Legendi]

Hi All,

I have encountered a strange behaviour, and it is not clear for me if it
is a bug or I have just skipped an important part in the documentation.

When I create an IList instance, put some mutable object in it and
change its value, it is not reflected in the stored IList.

Here's an example what I mean:

// Some dummy wrapper class
class MyMutableWrapper implements Serializable {
private static final long serialVersionUID = 1L;
int value = 0;

public int getValue() {
return value;
}

public void setValue(final int value) {
this.value = value;
}
}

What I would like to do is something like the following:

final IList<MyMutableWrapper> list = hazelcast.getList( "updatedList" );

for (int i = 0; i < 10; ++i) {
list.add( new MyMutableWrapper() );
}

// Before setting, should be 000...0

list.get( 4 ).setValue( 1 );

// After update, should be 0001000...0

// Check if update was successful
assertEquals( 1, list.get( 4 ).getValue() );

A strange thing is that this is working if I'm using only one Hazelcast
instance. Should I use some sort of explicit synchronization in this
particular case or something?

I would thank anyone a small clarification in the subject. Any pointers
or references to the documentation is more than welcome.

A workaround for my case is to replace the element with a new
MyMutableWrapper instance (containing the updated state), it seems
working; although I would like to understand what's going on here.

I've also attached a small test case that reproduces the problem. I'm
not sure but I think the same stands for IMap as well.

Thank you all in advance!

All the best,
Richard
--
Richard O. Legendi
PhD Student
E�tv�s Lor�nd University, Faculty of Informatics
Department of Programming Languages and Compilers
http://people.inf.elte.hu/legendi/

[Talip Ozturk]

When you do list.get(4), you get the 'hard copy' of the item at index
4. So you should put it back after updating:

MyMutableWrapper item = list.get(4); // get the copy
item.setValue(1); // update the copy
list.set(4, item); // put it back.

Same goes for all other distributed data structures.

http://twitter.com/oztalip

> Eötvös Loránd University, Faculty of Informatics

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> http://people.inf.elte.hu/legendi/
>

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[Richard O. Legendi]

Cool, thanks for the quick reply, Talip!

Best,

Richard
--
Richard O. Legendi
PhD Student

E�tv�s Lor�nd University, Faculty of Informatics

Department of Programming Languages and Compilers
http://people.inf.elte.hu/legendi/

>> E�tv�s Lor�nd University, Faculty of Informatics