RFR: 8178489: Make align functions more type safe and consistent

[Stefan Karlsson]

Thanks, Robbin.

StefanK

On 2017-07-04 10:44, Robbin Ehn wrote:
> Looks good.
> 
> Thanks, Robbin
> 
> On 06/30/2017 11:16 AM, Stefan Karlsson wrote:
>> Hi all,
>>
>> Please review this patch to make the align functions more type safe 
>> and consistent.
>>
>> http://cr.openjdk.java.net/~stefank/8178489/webrev.00
>> https://bugs.openjdk.java.net/browse/JDK-8178489
>>
>> Note that this patch needs to be applied on top of the following 
>> patches that are out for review:
>>   http://cr.openjdk.java.net/~stefank/8178491/webrev.02
>>   http://cr.openjdk.java.net/~stefank/8178495/webrev.01
>>
>> Currently, the align functions forces the user to often explicitly 
>> cast either the input parameters, or the return type, or both.
>>
>> Two examples of the current API:
>> inline intptr_t align_size_up(intptr_t size, intptr_t alignment);
>> inline void* align_ptr_up(const void* ptr, size_t alignment);
>>
>> I propose that we change the API to use templates to return the 
>> aligned value as the same type as the type of the unaligned input.
>>
>> The proposed API would look like this:
>>
>> template <typename T, typename A>
>> inline T align_size_up(T size, A alignment);
>>
>> template <typename T, typename A>
>> inline T* align_ptr_up(T* ptr, A alignment);
>>
>> and a follow-up RFE (JDK-8178499) would get rid of _size_ and _ptr_ 
>> from the names.
>>
>> Usages of these align functions would then look like:
>>
>> size_t aligned_size = align_up(alloc_size, os::vm_page_size())
>> HeapWord* aligned_top = align_up(top, region_size)
>>
>> Please, take an extra close look at the reinterpret_cast I added in 
>> atomic.hpp. This was needed because the align_ptr_down now returns T* 
>> and not void*, and the compiler complained when we tried to do a 
>> static cast from a volatile jbyte* to a volatile jint*.
>>
>> Tested with the align unit test and JPRT.
>>
>> Thanks,
>> StefanK