RFR: [6904367]: (coll) IdentityHashMap is resized before exceeding the expected maximum size

[Jeff Hain]

>So, I reverted this change to the original code, but added a single 
>check of the current table size before doing any modifications to the map.
>This is to address the issue #4, and this doesn't seem to introduce any 
>significant penalty.
>
>Would you please help review the updated webrev:
>
>http://cr.openjdk.java.net/~igerasim/6904367/3/webrev/
>
>Sincerely yours,
>
>Ivan

It's possible to avoid the capacity test for the general case:
put {
    ...while loop...

    if (size < threshold) {
        modCount++;
        tab[i] = k;
        tab[i + 1] = value;
        ++size;
    } else {
        putAndResize(k, value, i);
    }
    return null;
}
private void putAndResize(Object k, Object value, int i) {
    if (size == MAXIMUM_CAPACITY - 1)
        throw new IllegalStateException("Capacity exhausted.");
    modCount++;
    Object[] tab = table;
    tab[i] = k;
    tab[i + 1] = value;
    ++size;
    resize(tab.length); // len == 2 * current capacity.
}

It seems faster more often than not, but it adds more (and copied) code:
not sure it's worth it.

-Jeff