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

[Johan Sjölen]

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!

Found 1issue

src/hotspot/os/posix/perfMemory_posix.cpp line 472:

> 470:         // this check is added to protect against an observed problem
> 471:         // with getpwuid_r() on RedHat 9 where getpwuid_r returns 0,
> 472:         // indicating success, but has p == null. This was observed when

nullptr

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