What causes "IllegalStateException" in pinpoint-apm/pinpoint?

Only call remove() immediately after a successful next(), once per element

pinpoint-apm/pinpoint · error · java.lang.IllegalStateException

IllegalStateException

Error message

IllegalStateException

What it means

Iterator.remove() throws IllegalStateException when lastReturned is null, meaning remove() was called before any next() call, twice in a row, or after the entry was already removed. Each next() must be paired with at most one remove().

Source

Thrown at commons-profiler/src/main/java/com/navercorp/pinpoint/common/profiler/concurrent/jsr166/ConcurrentWeakHashMap.java:1209

            return false;
        }

        HashEntry<K,V> nextEntry() {
            do {
                if (nextEntry == null)
                    throw new NoSuchElementException();

                lastReturned = nextEntry;
                currentKey = lastReturned.keyRef.get();
                advance();
            } while (currentKey == null); // Skip GC'd keys

            return lastReturned;
        }

        public void remove() {
            if (lastReturned == null)
                throw new IllegalStateException();
            ConcurrentWeakHashMap.this.remove(currentKey);
            lastReturned = null;
        }
    }

    final class KeyIterator
            extends HashIterator
            implements Iterator<K>, Enumeration<K>
    {
        public K next()        { return super.nextEntry().keyRef.get(); }
        public K nextElement() { return super.nextEntry().keyRef.get(); }
    }

    final class ValueIterator
            extends HashIterator
            implements Iterator<V>, Enumeration<V>
    {
        public V next()        { return super.nextEntry().value; }

View on GitHub (pinned to 744c3d3075)

Solutions

Only call remove() immediately after a successful next(), once per element
Move the remove() call inside the loop body guarded by the per-element condition
Remove via map.remove(key) directly instead of the iterator when state is unclear

Example fix

// before
for (K k : map.keySet()) {
    if (expired(k)) map.remove(k);
}
it.remove(); // stray call
// after
Iterator<K> it = map.keySet().iterator();
while (it.hasNext()) {
    K k = it.next();
    if (expired(k)) { it.remove(); }
}

Defensive patterns

Strategy: try-catch

Try / catch

try { it.remove(); } catch (IllegalStateException e) { /* remove without preceding next(): fix loop structure */ }

Prevention

Pair every remove() with exactly one preceding next() call in the same loop iteration
Never call it.remove() outside the loop body
Prefer collecting keys then map.removeAll(collected) for bulk cleanup

When it happens

Trigger: it.remove() as the first call on a fresh iterator; calling remove() twice after a single next(); calling remove() after a previous remove() set lastReturned = null.

Common situations: Conditional cleanup loops that call remove() outside the per-element branch; copy-pasted remove logic executed on an unused iterator.

Related errors

AI-assisted analysis of pinpoint-apm/pinpoint@744c3d3075 (2026-09-07). Data as JSON: /api/errors/25e73e3c9b96f58f. Report an issue: GitHub.