NPE on nextEntry() for Int2ObjectOpenHashSet.values().iterator()

[Alex Fiennes]

Hi,

I am getting an odd exception when iterating across values with fastutil 7.0.13 on an Int2ObjectOpenHashSet which appears to be a problem in the fastutil implementation.

I have a nice simple loop of:

Iterator<Object> i = map.values.iterator();

while (i.hasNext()) { System.out.println(i.next()) }

but I am getting a:

     [java] Caused by: java.lang.NullPointerException

     [java] at it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap$MapIterator.nextEntry(Int2ObjectOpenHashMap.java:730)

     [java] at it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap$ValueIterator.next(Int2ObjectOpenHashMap.java:1033)

which appears to be from:

final int k = wrapped.getInt(-pos - 1);

but wrapper is documented as:

/**

* A lazily allocated list containing keys of entries that have wrapped

* around the table because of removals.

*/

and I have not been invoking remove and therefore wrapper has not been allocated hence the NPE.

so there is some situation where...

if (--pos < 0) {

...is true despite not having invoked remove() on the iterator().  

after this point I am getting other weird errors on the rehash functionality like:

java.lang.ArrayIndexOutOfBoundsException: -1

at it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap.rehash(Int2ObjectOpenHashMap.java:1167)

at it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap.insert(Int2ObjectOpenHashMap.java:346)

at it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap.put(Int2ObjectOpenHashMap.java:353)

so obviously something has got really confused.  I have the map in question protected by a ReadWriteLock so there are no concurrent writes.  Can you think of anything that I might be doing to provoke this behaviour, and what further information would be useful to help diagnose the problem?

many thanks

Alex

[Sebastiano Vigna]

I would look for map modifications happening during the iteration. That's usually the case.

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