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

[Robbin Ehn]

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