RFR: JDK-8301480: Replace NULL with nullptr in os/posix

[David Holmes]

On Tue, 31 Jan 2023 10:16:00 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

> Hi, this PR changes all occurrences of NULL to nullptr for the subdirectory os/posix. 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!

Generally good but one bug. Thanks

src/hotspot/os/posix/signals_posix.cpp line 1347:

> 1345:                                 EXC_MASK_BAD_ACCESS | EXC_MASK_ARITHMETIC
> 1346:                                   AARCH64_ONLY(| EXC_MASK_BAD_INSTRUCTION),
> 1347:                                 MACH_PORT_nullptr,

This is wrong. Needs reverting. (How did this build on macOS?)

-------------

Changes requested by dholmes (Reviewer).

PR: https://git.openjdk.org/jdk/pull/12316