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document pthread_getattr_np

.\" $NetBSD: pthread_attr_get_np.3,v 1.4 2010/08/06 05:35:42 christos Exp $
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.\" Copyright (c) 2010 Jukka Ruohonen <jruohonen@iki.fi>
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.Dd August 6, 2010
.Dt PTHREAD_ATTR_GET_NP 3
.Os
.Sh NAME
.Nm pthread_attr_get_np
.Nd get attributes of existing thread
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In pthread.h
.Ft int
.Fn pthread_attr_get_np "pthread_t thread" "pthread_attr_t *attr"
.Ft int
.Fn pthread_getattr_np "pthread_t thread" "pthread_attr_t *attr"
.Sh DESCRIPTION
The
.Fn pthread_attr_get_np
and
.Fn pthread_getattr_np
functions can be used to retrieve attributes of a running
.Fa thread .
The result is stored to
.Fa attr .
.Pp
For
.Fn pthread_attr_get_np
.Fa attr
should be initialized prior to the call by using
.Xr pthread_attr_init 3 .
.Fn pthread_getattr_np
does this automatically.
.Pp
For both functions
.Fa attr
should be freed when it is not in use anymore with
.Xr pthread_attr_destroy 3 .
.Pp
Most fields of
.Fa attr
are the same ones provided during thread creation time as a parameter to
.Xr pthread_create 3 .
The exceptions include:
.Bl -bullet -offset indent
.It
The detach state -- a joinable thread
may have detached itself after the creation.
.It
The guard size, which may vary if the application
has allocated its own thread stack.
.It
The stack address and size;
.Fn pthread_attr_get_np
will always return the thread's real stack address and size,
regardless of the values in the original attributes structure.
.El
.Pp
The returned
.Vt pthread_attr_t
structure is supposed to be used in conjunction with the
.Fn pthread_attr_get*
functions to retrieve individual values from the structure.
When the returned
.Fa attr
is no longer needed, it should be destroyed by using
.Xr pthread_attr_destroy 3 .
.Sh RETURN VALUES
Upon successful completion,
.Fn pthread_attr_get_np
and
.Fn pthread_getattr_np
return 0.
Otherwise an error number is returned to indicate the error.
.Sh COMPATIBILITY
The
.Fn pthread_attr_get_np
and
.Fn pthread_getattr_np
functions are non-standard extensions.
.Sh ERRORS
The
.Fn pthread_attr_get_np
and
.Fn pthread_getattr_np
functions will fail if:
.Bl -tag -width Er
.It Bq Er ENOMEM
Insufficient memory.
.It Bq Er ESRCH
Non-existent
.Fa thread .
.El
.Sh SEE ALSO
.Xr pthread 3 ,
.Xr pthread_attr 3