pthread_attr_get_np(3): Revamp

Fix and more thoroughly describe the attributes object lifecycle.

Also, correct the text about which attributes' values are reported.

Add the ENOMEM error.

While here, rephrase unclear passages, add references and fix the
example's style.

Reviewed by:            kib, emaste
Approved by:            emaste (mentor)
MFC after:              2 weeks
Sponsored by:           The FreeBSD Foundation
Differential Revision:  https://reviews.freebsd.org/D43330

1 files changed, 49 insertions, 35 deletions

diff --git a/share/man/man3/pthread_attr_get_np.3 b/share/man/man3/pthread_attr_get_np.3
index a13835287d7f..07153586c1b2 100644
--- a/share/man/man3/pthread_attr_get_np.3
+++ b/share/man/man3/pthread_attr_get_np.3
@@ -1,5 +1,10 @@
 .\" Copyright (c) 2002,2003 Alexey Zelkin <phantom@FreeBSD.org>
 .\" All rights reserved.
+.\" Copyright (c) 2024 The FreeBSD Foundation
+.\"
+.\" Portions of this documentation were written by Olivier Certner
+.\" <olce@FreeBSD.org> at Kumacom SARL under sponsorship from the
+.\" FreeBSD Foundation.
 .\"
 .\" Redistribution and use in source and binary forms, with or without
 .\" modification, are permitted provided that the following conditions
@@ -22,12 +27,12 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd October 12, 2021
+.Dd January 5, 2024
 .Dt PTHREAD_ATTR_GET_NP 3
 .Os
 .Sh NAME
 .Nm pthread_attr_get_np
-.Nd get attributes of existent thread
+.Nd get attributes of an existing thread
 .Sh LIBRARY
 .Lb libpthread
 .Sh SYNOPSIS
@@ -37,51 +42,54 @@
 .Sh DESCRIPTION
 The
 .Fn pthread_attr_get_np
-function is used to get existent thread's attributes.
-Most fields of
-.Vt pthread_attr_t
-structure are exact values of attributes provided at thread creation
-time (as parameter to
-.Xr pthread_create 3
-function), except for the stack address.
-.Pp
-Value returned as
-.Fa dst
-is supposed to be used in conjunction with
-.Fn pthread_attr_get*
-functions to retrieve individual values from
+function is used to retrieve the attributes of the specified thread into an
+existing
 .Vt pthread_attr_t
 structure.
-Parameter
-.Fa dst
-should point to allocated memory area big enough to fit this structure.
+The attributes' values are the current ones for the target thread, except for
+the stack top address if not properly aligned for the architecture, since in
+this case its value has been adjusted internally before use.
 .Pp
-It is HIGHLY RECOMMENDED to use
+Argument
+.Fa dst
+must be a pointer to a valid attributes object
+.Po
+it was initialized at some point by
 .Xr pthread_attr_init 3
-function to allocate attribute storage.
-.Sh IMPLEMENTATION NOTES
-The
-.Fn pthread_attr_get_np
-function will always return a pointer to the thread's real stack address,
-regardless of its value in the original attributes structure.
+and was not destroyed since then
+.Pc .
+After a successful call to
+.Fn pthread_attr_get_np ,
+the individual attributes' values can be retrieved as usual via the
+corresponding accessor functions as documented in
+.Xr pthread_attr 3 .
+After a failed call to
+.Fn pthread_attr_get_np ,
+the object pointed to by
+.Fa dst
+is left unmodified, and can continue to be used as if the failed call never
+happened.
 .Sh RETURN VALUES
 If successful,
 .Fn pthread_attr_get_np
 function returns 0.
 Otherwise, an error number is returned to indicate the error.
 .Sh EXAMPLES
+This function retrieves the stack size of the thread specified by the
+.Fa pid
+argument:
 .Bd -literal
 size_t
-my_thread_stack_size(pthread_t pid)
+my_thread_stack_size(pthread_t tid)
 {
-    pthread_attr_t attr;
-    size_t size;
+	pthread_attr_t attr;
+	size_t size;
 
-    pthread_attr_init(&attr);
-    pthread_attr_get_np(pid, &attr);
-    pthread_attr_getstacksize(&attr, &size);
-    pthread_attr_destroy(&attr);
-    return(size);
+	pthread_attr_init(&attr);
+	pthread_attr_get_np(tid, &attr);
+	pthread_attr_getstacksize(&attr, &size);
+	pthread_attr_destroy(&attr);
+	return (size);
 }
 .Ed
 .Sh ERRORS
@@ -90,12 +98,16 @@ The
 function will fail if:
 .Bl -tag -width Er
 .It Bq Er EINVAL
-Invalid value for one of given parameters.
+One of the arguments has an invalid value.
 .It Bq Er ESRCH
 No thread could be found corresponding to that specified by the given
 thread ID.
+.It Bq Er ENOMEM
+There was not enough memory to allocate additional storage needed by the attributes
+object's implementation.
 .El
 .Sh SEE ALSO
+.Xr pthread_attr 3 ,
 .Xr pthread_attr_destroy 3 ,
 .Xr pthread_attr_getdetachstate 3 ,
 .Xr pthread_attr_getinheritsched 3 ,
@@ -111,4 +123,6 @@ thread ID.
 The
 .Fn pthread_attr_get_np
 function and this manual page were written by
-.An Alexey Zelkin Aq Mt phantom@FreeBSD.org .
+.An Alexey Zelkin Aq Mt phantom@FreeBSD.org ,
+and the latter was revised by
+.An Olivier Certner Aq Mt olce@FreeBSD.org .