RFR(XS): JDK-8214272: Don't use memset to initialize arrays of MemoryUsage in memoryManager.cpp

[Roman Kennke]

Oh. Right. There is always something to learn about C++ :-) Your patch
looks good then. And actually, may want to fix 'my' change too, if you
feel like it. And I believe gcc8 prints more similar warnings.

Thanks,
Roman


> Doesn't "= MemoryUsage()" actually imply "delete onstack MemoryUsage"
> after copying? Probably safe here but it may be not safe in general.
> 
> -Dmitry
> 
> On 11/27/18 5:14 PM, Roman Kennke wrote:
>> I think Aleksey's version is clearer. I used a similar approach in a fix
>> for the same issue:
>>
>> http://hg.openjdk.java.net/jdk/jdk/rev/710e5a66a64e
>>
>> Roman
>>
>>
>>> Placement new sets values placed in arrays. The arrays as a whole are
>>> managed as before. I.e.:
>>>
>>> GCStatInfo::~GCStatInfo() {
>>>    FREE_C_HEAP_ARRAY(MemoryUsage*, _before_gc_usage_array);
>>>    FREE_C_HEAP_ARRAY(MemoryUsage*, _after_gc_usage_array);
>>> }
>>>
>>> -Dmitry
>>>
>>> On 11/27/18 5:00 PM, Aleksey Shipilev wrote:
>>>> On 11/27/18 2:51 PM, Dmitry Chuyko wrote:
>>>>> rfe: https://bugs.openjdk.java.net/browse/JDK-8214272
>>>>> webrev: http://cr.openjdk.java.net/~dchuyko/8214272/webrev.00/
>>>> Ummmm. Aren't you leaking memory by calling "new" without "delete"?
>>>>
>>>> Consider this instead:
>>>>
>>>> diff -r a554db76b2e9 src/hotspot/share/services/memoryManager.cpp
>>>> --- a/src/hotspot/share/services/memoryManager.cpp      Fri Nov 23
>>>> 11:22:31 2018 +0100
>>>> +++ b/src/hotspot/share/services/memoryManager.cpp      Tue Nov 27
>>>> 14:56:09 2018 +0100
>>>> @@ -169,7 +169,8 @@
>>>>      _start_time = 0L;
>>>>      _end_time = 0L;
>>>> -  size_t len = _usage_array_size * sizeof(MemoryUsage);
>>>> -  memset(_before_gc_usage_array, 0, len);
>>>> -  memset(_after_gc_usage_array, 0, len);
>>>> +  for (int i = 0; i < _usage_array_size; i++) {
>>>> +    _before_gc_usage_array[i] = MemoryUsage();
>>>> +    _after_gc_usage_array[i]  = MemoryUsage();
>>>> +  }
>>>>    }
>>>>
>>>> See, for example:
>>>>    https://bugs.openjdk.java.net/browse/JDK-8213745
>>>>
>>>> -Aleksey
>>>>

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