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

[Roman Kennke]

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
>>