Sometimes constraints are questionable

[Jim Laskey]

I'm working through https://bugs.openjdk.java.net/browse/JDK-8230744 <https://bugs.openjdk.java.net/browse/JDK-8230744> Several classes throw OutOfMemoryError without message .

I'm wondering why hugeCapacity in src/jdk.zipfs/share/classes/jdk/nio/zipfs/ByteArrayChannel.java is defined as 

    /**
     * The maximum size of array to allocate.
     * Some VMs reserve some header words in an array.
     * Attempts to allocate larger arrays may result in
     * OutOfMemoryError: Requested array size exceeds VM limit
     */
    private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;

    /**
     * Increases the capacity to ensure that it can hold at least the
     * number of elements specified by the minimum capacity argument.
     *
     * @param minCapacity the desired minimum capacity
     */
    private void grow(int minCapacity) {
        // overflow-conscious code
        int oldCapacity = buf.length;
        int newCapacity = oldCapacity << 1;
        if (newCapacity - minCapacity < 0)
            newCapacity = minCapacity;
        if (newCapacity - MAX_ARRAY_SIZE > 0)
            newCapacity = hugeCapacity(minCapacity);
        buf = Arrays.copyOf(buf, newCapacity);
    }

    private static int hugeCapacity(int minCapacity) {
        if (minCapacity < 0) // overflow
            throw new OutOfMemoryError();
        return (minCapacity > MAX_ARRAY_SIZE) ?
            Integer.MAX_VALUE :
            MAX_ARRAY_SIZE;
    }

It just seems that it's pushing the inevitable off to Arrays.copyOf.  Shouldn't it be:

    private static int hugeCapacity(int minCapacity) {
        if (minCapacity < 0 || minCapacity > MAX_ARRAY_SIZE) {
            throw
                new OutOfMemoryError("ByteArrayChannel exceeds maximum size: " +
                                      MAX_ARRAY_SIZE);
        }
        
        return MAX_ARRAY_SIZE;
    }

Real question: is there some hidden purpose behind this kind of logic?


Cheers,

-- Jim