[PATCH] pthread: add PTHREAD_NULL

[Collin Funk]

Hi Alyssa,

Alyssa Ross <hi@alyssa.is> writes:

> New in POSIX.1-2024.
>
> In htl, pthread_t values are integers starting at 1, so 0 is a safe
> null value.
>
> In nptl, pthread_t values are non-null pointers, so 0 is a safe null
> value.
> ---
> I wasn't sure whether this should be behind a __USE macro, but there
> isn't one for POSIX.1-2024 yet:
> https://inbox.sourceware.org/libc-alpha/d34488044ace7c01311fb1c1948e65a050e93252.1747972803.git.collin.funk1@gmail.com/
>
>  manual/threads.texi    | 5 +++++
>  sysdeps/htl/pthread.h  | 2 ++
>  sysdeps/nptl/pthread.h | 3 +++
>  3 files changed, 10 insertions(+)
>
> diff --git a/manual/threads.texi b/manual/threads.texi
> index 1e9be32d66..d3692e8939 100644
> --- a/manual/threads.texi
> +++ b/manual/threads.texi
> @@ -1099,6 +1099,11 @@ This function gets the kind of mutex @var{mutex} is.
>  @node POSIX Threads Other APIs
>  @subsection POSIX Threads Other APIs
>  
> +@deftypevr Macro pthread_t PTHREAD_NULL
> +@standards{POSIX.1-2024, pthread.h}
> +A value for pthread_t that is not considered equal to any thread ID.
> +@end deftypevr
> +
>  @deftypefun int pthread_equal (pthread_t @var{thread1}, pthread_t @var{thread2})
>  Compares two thread IDs.  If they are the same, returns nonzero, else returns zero.
>  @manpagefunctionstub{pthread_equal, 3}
> diff --git a/sysdeps/htl/pthread.h b/sysdeps/htl/pthread.h
> index a299fec278..d490f3cdf8 100644
> --- a/sysdeps/htl/pthread.h
> +++ b/sysdeps/htl/pthread.h
> @@ -55,6 +55,8 @@ __BEGIN_DECLS
>  
>  #include <bits/pthread.h>
>  
> +#define PTHREAD_NULL ((pthread_t)0)
> +
>  /* Possible values for the process shared attribute.  */
>  #define PTHREAD_PROCESS_PRIVATE __PTHREAD_PROCESS_PRIVATE
>  #define PTHREAD_PROCESS_SHARED __PTHREAD_PROCESS_SHARED
> diff --git a/sysdeps/nptl/pthread.h b/sysdeps/nptl/pthread.h
> index 92957a620d..b47b732a9f 100644
> --- a/sysdeps/nptl/pthread.h
> +++ b/sysdeps/nptl/pthread.h
> @@ -33,6 +33,9 @@
>  # include <bits/pthread_stack_min-dynamic.h>
>  #endif
>  
> +#define PTHREAD_NULL ((pthread_t)0)
> +
> +
>  /* Detach state.  */
>  enum
>  {
>
> base-commit: 720e89163702ffa1e921d926b6c36b53c3ccbee4

I don't think this will cause conform tests to fail since PTHREAD_* is
allowed. But it should probably be hidden under __USE_XOPEN2K24 which is
not yet introduced. I have an old patch that is still waiting on review
[1].

Collin

[1] https://inbox.sourceware.org/libc-alpha/d34488044ace7c01311fb1c1948e65a050e93252.1747972803.git.collin.funk1@gmail.com/