Thanks David will run with that,
> On May 31, 2020, at 8:34 PM, David Holmes <david.hol...@oracle.com> wrote: > > On 31/05/2020 12:29 am, Jim Laskey wrote: >> 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(); > > Not sure how we could have minCapacity < 0 at this point. It should have been > checked before the call to grow, and grow will not make it negative. > >> return (minCapacity > MAX_ARRAY_SIZE) ? >> Integer.MAX_VALUE : >> MAX_ARRAY_SIZE; > > That's a bug plain and simple. It should never report a size > 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; >> } > > That seems more appropriate to me - modulo the question mark over minCapacity > being negative. > >> Real question: is there some hidden purpose behind this kind of logic? > > The basic strategy is to double the current capacity unless that will trigger > an unnecessary exception, in which case just use the requested capacity, but > again watch for the implementation limits. > > Cheers, > David > ----- > >> Cheers, >> -- Jim
