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

Peter Levart peter.levart at gmail.com
Wed Jul 9 07:33:29 UTC 2014

On 07/09/2014 09:23 AM, Peter Levart wrote:

On 07/09/2014 02:46 AM, Martin Buchholz wrote: Let me understand - you're worried that when size is MAXCAPACITY - 1, then a call to putAll that does not actually add any elements might throw? This is not possible, because resize() is only called from putAll(map) if argument map.size() > this.size. At least one element will be added to the map and it's correct to throw if current size == MAXCAPACITY - 1.

...at least if the argument map obeys the rules of Map contract. Even if it's a HashMap or another IdentityHashMap, it should not contain the same INSTANCE of the key in two or more mappings, should not "overshoot" reporting it's size() and should be stable during the whole putAll() operation... So calling IHM.addAll() with a live changing ConcurrentHashMap is not advisable. Even then, addAll() could only throw, because at some point the argument's size indicated that IHM could reach it's max. capacity.

Peter

Well, I'm having a hard time considering that corner case a bug, given how unusable the map is at this point. It seems even this corner case is not present.

Your suggested fix of returning immediately in case of no resize would cause put to succeed and reach size == MAXCAPACITY, which you were trying to prevent. That's not possible either, since resize() is always called from put() with current table.length, which makes newLength == 2 * oldLength, therefore (oldLength >= newLength) will never succeed in this case. Peter

On Tue, Jul 8, 2014 at 5:25 PM, Ivan Gerasimov <ivan.gerasimov at oracle.com <mailto:ivan.gerasimov at oracle.com>> wrote: On 09.07.2014 3:20, Martin Buchholz wrote: I agree with Peter that we do not need to increment modCount on resize. My latest webrev is again "done". Ivan, feel free to take over. Yes, thanks! The fix is much much better now. I think I see yet another very minor glitch, though. If the table is already of size 2 * MAXIMUMCAPACITY, and we're merging in another map, which has more elements with putAll(), resize() will be called and it will throw, even though all the elements could fit into the map due to the key duplicates. To avoid this the following check should be done first in resize(): 469 if (oldLength >= newLength) 470 return false; Sincerely yours, Ivan

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