Request for reviews (M): 7017124: VM statistic use 32-bit values which may overflow
David.Holmes at oracle.com
Thu Feb 3 18:37:10 PST 2011
Vladimir Kozlov said the following on 02/04/11 12:28:
> Vladimir Kozlov wrote:
>> David Holmes wrote:
>>> Vladimir Kozlov said the following on 02/04/11 10:05:
>>>> Added new Atomic method inc_counter() to increment long values,
>>>> it is not precise on MP (lock is not used) but it is fine.
>>> I strongly disagree! At least it has no place being in the Atomic::
>>> set of functions as it is not atomic. It is not even monotonic! It is
>> It is atomic since it loads and stores all 64 bits of julong atomically.
>> Why we can call atomic methods Atomic::load() and Atomic::store()
>> which are used by new method but not this method?
>> And it is monotonic since value in memory only grows.
> OK, I am taking monotonic statement back. Yes, the value may decrease
> if a thread loads value before other threads but stores it after other
> threads already updated it. But I still want to use atomic load and store
> since otherwise the value will be garbage.
I totally agree that you want the functionality of inc_counter, with
atomic load and store, but that function is not itself atomic and so
does not belong in the Atomic class.
>>> extremely deceptive to do this. By all means change to julong where
>>> needed, but unless they are truly going to be atomic updates (I
>>> understand the overhead makes that prohibitive) then leave them as
>>> simply x+=i; statements.
>>>> Fixed several output formats to use VM FORMAT macros.
>>>> I have to remove v9 check assert from Atomic_move_long() since
>>>> it is called before VM_Version is initialized and C2 is built
>>>> for v9 only anyway.
>>>> Removed unused Chunk::clean_chunk_pool().
>>> Used by CI.
>>>> I fixed only statistic which was interesting to me.
>>> So the CR is misleading. It purports to deal with 32-bit stat
>>> overflows but in fact only deals with some stats, and primarily you
>>> are using this to define PrintMallocStat - so the CR should reflect
>>> that: "Fix some VM stats to avoid 32-bit overflow"
>>> + "print malloc/free statictics") \
>>> Typo: statictics
>>> This change seems unrelated to the CR.
>> I removed it from these changes.
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