Integrated: JDK-8256287: [windows] add loop fuse to map_or_reserve_memory_aligned

[Thomas Stuefe]

On Thu, 12 Nov 2020 15:59:44 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> Hi,
> 
> may I please have reviews for this little fix:
> 
> On windows, `map_or_reserve_memory_aligned()` attempts to allocate aligned memory by:
> 1) reserving larger area
> 2) releasing it
> 3) attempting to re-reserve into the vacated address space a smaller area at the aligned start address
> 
> Since this may fail (between (2) and (3) someone may have grabbed part of that address space concurrently), we do this in a loop. However, when failing to release it we will loop-reserve endlessly.
> 
> This is one of the reasons for JDK-8255954 whose root cause will be fixed with JDK-8255978. But we should guard against endless loops independently from that.
> 
> This patch:
> - limits the number we try this to 20. If in 20 cases someone else grabs address space concurrently, something is off...
> - now correctly handles the return code of the release operation (1): in debug we assert, since if release_memory() fails something is wrong and we should take a look. In the release case, we now return an error.
> 
> 
> Thanks!

This pull request has now been integrated.

Changeset: 0357db35
Author:    Thomas Stuefe <stuefe at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/0357db35
Stats:     16 lines in 1 file changed: 4 ins; 1 del; 11 mod

8256287: [windows] add loop fuse to map_or_reserve_memory_aligned

Reviewed-by: luhenry, iklam, minqi

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PR: https://git.openjdk.java.net/jdk/pull/1191