Re: Collections.synchronizedMap - worth using?

From:

"Daniel Pitts" <googlegroupie@coloraura.com>

Newsgroups:

comp.lang.java.programmer

Date:

1 Feb 2007 12:08:44 -0800

Message-ID:

<1170360524.848128.88680@k78g2000cwa.googlegroups.com>

On Jan 30, 11:18 am, Ian Pilcher <i.pilc...@comcast.net> wrote:

I've got a map that will be access by multiple threads, so I'm
considering using Collections.synchronizedMap to "wrap" it. There will
be occasions, though, where I will need to manually synchronize.

    synchronized (syncMap)
    {
        if (syncMap.containsKey(key))
            throw new AlreadyGotOneException();
        syncMap.put(key, value);
    }

This "double synchronization" seems inelegant, and possibly wasteful.

Is there a consensus on the best practice in this situation?

Thanks!

That seems to be a good enough implementation.

I have a few questions, though.
Is the "AlreadyGotOneException" a sort of assertion against programmer
error?
Whether or not it is, does this mean the state of your application is
probably foobar?

If you are simply testing for programmer (or configuration) error,
then it might be better to do this instead:
oldValue = syncMap.put(key, value);
assert oldValue != null;
This has two side effects:
1. No extra sync
2. the new value does replace the old value, but an exception is still
thrown.

Hope this all helps,
Daniel.