Request for review: 7046490 - Preallocated OOME objects should obey Throwable stack trace protocol

[David Holmes]

Paul Hohensee said the following on 07/19/11 13:32:
> Looks good, except, could you use obj_field() in unassigned_stacktrace() 
> instead of checking UseCompressedOops there?

Thanks Paul.

I don't think I can use obj_field() as it is for accessing instances and 
this is a static field. I copied the code for reading the static field 
from the java.lang.ref functions:

2286 // Support for java_lang_ref_Reference
2287 oop java_lang_ref_Reference::pending_list_lock() {
2288   instanceKlass* ik = 
instanceKlass::cast(SystemDictionary::Reference_klass());
2289   address addr = ik->static_field_addr(static_lock_offset);
2290   if (UseCompressedOops) {
2291     return oopDesc::load_decode_heap_oop((narrowOop *)addr);
2292   } else {
2293     return oopDesc::load_decode_heap_oop((oop*)addr);
2294   }
2295 }
2296
2297 HeapWord *java_lang_ref_Reference::pending_list_addr() {
2298   instanceKlass* ik = 
instanceKlass::cast(SystemDictionary::Reference_klass());
2299   address addr = ik->static_field_addr(static_pending_offset);
2300   // XXX This might not be HeapWord aligned, almost rather be char *.
2301   return (HeapWord*)addr;
2302 }
2303
2304 oop java_lang_ref_Reference::pending_list() {
2305   char *addr = (char *)pending_list_addr();
2306   if (UseCompressedOops) {
2307     return oopDesc::load_decode_heap_oop((narrowOop *)addr);
2308   } else {
2309     return oopDesc::load_decode_heap_oop((oop*)addr);
2310   }
2311 }

David
-----

> 
> Paul
> 
> On 7/7/11 1:25 AM, David Holmes wrote:
>> http://cr.openjdk.java.net/~dholmes/7046490/webrev/
>>
>> This is a simple fix in the VM to honour the Throwable immutability 
>> protocol that was defined for Java 7. Pre-allocated Throwable 
>> instances are normally immutable, but that is not the case for a group 
>> of pre-allocated OutOfMemoryError instances. To conform to the 
>> protocol, when we set the backtrace (VM representation of the 
>> stackTrace) we have to set the stackTrace field to the sentinel value 
>> stored in the static Throwable.UNASSIGNED_STACK field.
>>
>> With this fix in place the workaround in Throwable.java, under 
>> 7045138, can be backed out.
>>
>> Thanks,
>> David
>>
>>
>>