Should we really consider this a VM bug? I'm not sure that it's a good idea to allocate a single object which size exceeds 4Gb (for a byte[] - due to the object header and array size field) - even on a 64-bit VM. An array with 2^32 elements is impossible, the maximum allowed by the size field is 2^32-1 which will be just as bad as 2^32-N for any other tiny positive N, for algorithms that love arrays of [base-2-] "round" sizes.
And then if this bug is fixed, it may have slightly different variations. For a long[] or double[] array, the allocation for the maximum size would exceed 32Gb, so it exceeds the maximum heap size for 64-bit HotSpot with CompressedOops. (Ok this is an artificial issue because we won't like have a 100% free heap, so the only impediment for "new long[2^32-1]" would be the array header.) My suggestion: impose some fixed N (maybe 64, or 0x100, ...), limiting arrays to 2^32-N (for ANY element type). The artificial restriction should be large enough to fit the object header of any vendor's JVM, plus the per-object overhead of any reasonable heap structure. This limit could be added to the spec, so the implementation is not a bug anymore :) and it would be a portable limit. Otherwise, some app may work reliably on HotSpot if it relies on the fact that 2^32-5 positions are possible, but may break on some other vendor's JVM where perhaps the implementation limit is 2^32-13 or something else. A+ Osvaldo 2010/3/9 Martin Buchholz <marti...@google.com> > On Tue, Mar 9, 2010 at 03:59, Ulf Zibis <ulf.zi...@gmx.de> wrote: > > In PriorityQueue: > > > > let's result newCapacity in 0xFFFF.FFFC =-4 > > then "if (newCapacity - MAX_ARRAY_SIZE > 0)" ---> false > > then Arrays.copyOf(queue, newCapacity) ---> > ArrayIndexOutOfBoundsException > > How could newCapacity ever become -4? > Since growth is by 50%. But even 100% looks safe... > > > Am I wrong ? > > > > 2.) Why don't you prefer a system-wide constant for MAX_ARRAY_SIZE ??? > > This should never become a public API - it's a bug in the VM. > > I prefer the duplication of code to creating a new external dependency. > > Martin > > > -Ulf >
