Request for review: 7110152 assert(size_in_words <= (julong)max_jint) failed: no overflow

[Bengt Rutisson]

Vladimir,

Thanks for looking at this!

On 2011-11-09 23:06, Vladimir Kozlov wrote:
> Why not change it in all CollectedHeap methods?

The other methods in CollectedHeap that use int for size are handling 
objects. Those should not have been affected by my other change (since 
it only changed the maximum array length).

I have not investigated whether or not it is possible to create an 
object (that is not an array) that will have a size larger than int. I 
assume that there is some limit to how many fields an object can have. 
But I don't know what that limit is and whether it will guarantee that 
the largest object fits into an int. It also seems much more unlikely 
that anyone would actually create such a large object.

I'd like to only change this for arrays now since we have failures in 
the nightlies. If you think it is ok I could create a separate CR to 
investigate whether or not the int object sizes in CollectedHeap are safe.

Bengt

>
> Vladimir
>
> Bengt Rutisson wrote:
>>
>> Hi all,
>>
>> Could I have a couple of reviews for this small change?
>> http://cr.openjdk.java.net/~brutisso/7110152/webrev.01/
>>
>> The problem is that CollectedHeap::array_allocate() takes its size as 
>> an int instead of a size_t. This was exposed by the fix I made to 
>> 7102044 recently.
>>
>> That change allows arrays to be max_jint long on 64 bit systems. This 
>> is correct since we can handle this size in a 64 bit size_t even when 
>> we add the object header. However, it will overflow an int.
>>
>> Here is a small reproducer that will trigger the assert mentioned in 
>> 7110152 when it is run on a 64 bit VM:
>>
>> public class MaxJIntArray {
>>     public static void main(String[] args) {
>>         final int MAX_JINT = 2147483647;
>>         double[] a = new double[MAX_JINT];
>>         System.out.println("Allocated a[" + a.length + "]");
>>     }
>> }
>>
>> The fix is to remove the assert (since it is too strict) and changing 
>> CollectedHeap::array_allocate() to take a size_t instead of an int.
>>
>> CR:
>> 7110152 assert(size_in_words <= (julong)max_jint) failed: no overflow
>> http://monaco.sfbay.sun.com/detail.jsf?cr=7110152
>>
>> Bengt