RFR: JDK-8301481: Replace NULL with nullptr in os/windows

[Johan Sjölen]

On Tue, 31 Jan 2023 10:16:14 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

> Hi, this PR changes all occurrences of NULL to nullptr for the subdirectory os/windows. Unfortunately the script that does the change isn't perfect, and so we
> need to comb through these manually to make sure nothing has gone wrong. I also review these changes but things slip past my eyes sometimes.
> 
> Here are some typical things to look out for:
> 
> 1. No changes but copyright header changed (probably because I reverted some changes but forgot the copyright).
> 2. Macros having their NULL changed to nullptr, these are added to the script when I find them. They should be NULL.
> 3. nullptr in comments and logs. We try to use lower case "null" in these cases as it reads better. An exception is made when code expressions are in a comment.
> 
> An example of this:
> 
> ```c++
> // This function returns null
> void* ret_null();
> // This function returns true if *x == nullptr
> bool is_nullptr(void** x);
> 
> 
> Note how `nullptr` participates in a code expression here, we really are talking about the specific value `nullptr`.
> 
> Thanks!

Found a couple of bugs:

1. thread_id was assigned with NULL, but thread_id is unsigned_long on Windows. Maybe this should actually be `uintptr_t`?
2. An (ignored according to MS docs) argument had type `DWORD`, not pointer.

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PR: https://git.openjdk.org/jdk/pull/12317