ADDITIONAL SYSTEM INFORMATION :
Fails on all OSs.

A DESCRIPTION OF THE PROBLEM :
In LinkedBlockingDeque.addAll() we first build up the chain of nodes and then add that chain in bulk to the existing nodes. We count the nodes in "int n" and then whilst holding the lock, we check that we haven't exceeded the capacity with "if (count + n <= capacity)". However, if we pass in a collection that has more than Integer.MAX_VALUE items in it, then we can overflow n, making it negative. Since "count + n" is also negative, we can add the chain to our last item, and thus we end up with a LinkedBlockingDeque with more than Integer.MAX_VALUE of items and a negative size(). stream().count() gives the correct number of items.

This happens both via the bulk add constructor LinkedBlockingDeque(Collection) and when we call addAll(Collection) directly.

REGRESSION : Last worked in version 8

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the code below using the following setting. You need a machine with a lot of memory:

-XX:+UnlockExperimentalVMOptions -Xmx90g -Xms90g -XX:+UseEpsilonGC -verbose:gc

To verify my fix that I've sent as PR, you will need to run it with 200 GB of memory. We verified it on a 400 GB machine.




EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
 Exception in thread "main" java.lang.IllegalStateException: Deque full
ACTUAL -
heinz$ java -XX:+UnlockExperimentalVMOptions -XX:+UseEpsilonGC -verbose:gc -Xmx90g -Xms90g tjsn/ideas2025/juc/NegativeSizedLinkedBlockingDeque
[0.004s][info][gc] Using Epsilon
[0.005s][warning][gc,init] Consider enabling -XX:+AlwaysPreTouch to avoid memory commit hiccups
[0.668s][info ][gc ] Heap: 92160M reserved, 92160M (100.00%) committed, 4610M (5.00%) used
[1.321s][info ][gc ] Heap: 92160M reserved, 92160M (100.00%) committed, 9218M (10.00%) used
[1.962s][info ][gc ] Heap: 92160M reserved, 92160M (100.00%) committed, 13826M (15.00%) used
[2.626s][info ][gc ] Heap: 92160M reserved, 92160M (100.00%) committed, 18434M (20.00%) used
[3.283s][info ][gc ] Heap: 92160M reserved, 92160M (100.00%) committed, 23042M (25.00%) used
[3.934s][info ][gc ] Heap: 92160M reserved, 92160M (100.00%) committed, 27650M (30.00%) used
[4.602s][info ][gc ] Heap: 92160M reserved, 92160M (100.00%) committed, 32258M (35.00%) used
[5.253s][info ][gc ] Heap: 92160M reserved, 92160M (100.00%) committed, 36866M (40.00%) used
[5.907s][info ][gc ] Heap: 92160M reserved, 92160M (100.00%) committed, 41474M (45.00%) used
[6.577s][info ][gc ] Heap: 92160M reserved, 92160M (100.00%) committed, 46082M (50.00%) used
[7.228s][info ][gc ] Heap: 92160M reserved, 92160M (100.00%) committed, 50690M (55.00%) used
[7.884s][info ][gc ] Heap: 92160M reserved, 92160M (100.00%) committed, 55298M (60.00%) used
[8.526s][info ][gc ] Heap: 92160M reserved, 92160M (100.00%) committed, 59906M (65.00%) used
[9.179s][info ][gc ] Heap: 92160M reserved, 92160M (100.00%) committed, 64514M (70.00%) used
[10.282s][info ][gc ] Heap: 92160M reserved, 92160M (100.00%) committed, 69122M (75.00%) used
[11.096s][info ][gc ] Heap: 92160M reserved, 92160M (100.00%) committed, 73730M (80.00%) used
[11.957s][info ][gc ] Heap: 92160M reserved, 92160M (100.00%) committed, 78338M (85.00%) used
lbd.size() = -2147483648
2147483648
[27.619s][info ][gc ] Heap: 92160M reserved, 92160M (100.00%) committed, 81942M (88.91%) used

---------- BEGIN SOURCE ----------
import java.util.*;
import java.util.concurrent.*;

// To see the issue, run with at least 90 GB of memory:
// -XX:+UnlockExperimentalVMOptions -Xmx90g -Xms90g -XX:+UseEpsilonGC -verbose:gc
// To verify the fix, run with at least 200 GB of memory:
// -XX:+UnlockExperimentalVMOptions -Xmx200g -Xms200g -XX:+UseEpsilonGC -verbose:gc
// To try on older versions of Java that don't have the EpsilonGC, you can use:
// -XX:+UseG1GC -verbose:gc -Xmx91g -Xms91g -XX:NewSize=89g
public class NegativeSizedLinkedBlockingDeque {
    public static void main(String... args) {
        HUUUGECollection list = new HUUUGECollection(Integer.MAX_VALUE + 1L);
        LinkedBlockingDeque<Integer> lbd = new LinkedBlockingDeque<>(10);
        lbd.addAll(list);
        System.out.println("lbd.size() = " + lbd.size());
        System.out.println(lbd.stream().count());
    }

    public static class HUUUGECollection extends AbstractCollection<Integer> {
        private final long size;

        public HUUUGECollection(long size) {
            this.size = size;
        }

        @Override
        public int size() {
            return size < Integer.MAX_VALUE ? (int) size : Integer.MAX_VALUE;
        }

        @Override
        public Iterator<Integer> iterator() {
            return new Iterator<Integer>() {
                private long count = 0;

                public boolean hasNext() {
                    return count < size;
                }

                public Integer next() {
                    if (!hasNext()) throw new NoSuchElementException();
                    count++;
                    return 42;
                }
            };
        }
    }
}
---------- END SOURCE ----------