[thirdparty/man-pages.git] / man3 / pthread_rwlockattr_setkind_np.3

.\"Copyright (c) 2010 Novell Inc., written by Robert Schweikert
.\"   <mtk.manpages@gmail.com>
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.TH PTHREAD_RWLOCKATTR_SETKIND_NP 3 2010-06-09 "Linux Programmer's Manual"
.SH NAME
pthread_rwlockattr_setkind_np, pthread_rwlockattr_getkind_np \- set/get 
the read-write lock kind of the thread read-write lock attribute object
.SH SYNOPSIS
.nf
.B #define _XOPEN_SOURCE 500
.B #include <pthread.h>

.BI "int pthread_rwlockattr_setkind_np (pthread_rwlockattr_t *" attr ,
.BI "                                   int" pref);
.BI "int pthread_rwlockattr_getkind_np (const pthread_rwlockattr_t *" attr ,
.BI "                                   int *" pref);
.sp
Compile and link with \fI\-pthread\fP.
.SH DESCRIPTION
The
.BR pthread_rwlockattr_setkind_np ()
function
sets the kind of read-write lock of the
thread read-write lock attribute object referred to by
.I attr
to the value specified with 
.IR pref .
The argument
.I pref
may be set to
.IR PTHREAD_RWLOCK_PREFER_READER_NP , 
.IR PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP ,
or
.IR  PTHREAD_RWLOCK_PREFER_WRITER_NP .
The default lock setting is
.IR PTHREAD_RWLOCK_PREFER_READER_NP .
A thread may hold multiple read locks, i.e. read locks are recursive. 
According to The Single Unix Specification, the behavior is unspecified when a
reader tries to place a lock, and there is no write lock but writers are
waiting. Giving preference to the reader, as is set by default with the
.IR PTHREAD_RWLOCK_PREFER_READER_NP value
implies that the reader will receive the requested lock, even if
a writer is waiting. As long as there are readers the writer will be
starved. Setting the kind to 
.IR PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP ,
avoids writer starvation as long as any read locking is not done in a
recursive fashion.

The
.BR pthread_rwlockattr_getkind_np ()
function
returns the value of the read-write lock attribute of the
thread read-write lock attribute object referred to by
.IR attr
in the pointer
.IR pref .
.SH RETURN VALUE
On success, these functions return 0;
on error,
.BR pthread_rwlockattr_setkind_np ()
returns a non-zero error number.
.SH ERRORS
.TP
.BR EINVAL
.I pref
is set to an unsupported value.
.SH BUGS
Setting the value read-write lock kind to
.IR  PTHREAD_RWLOCK_PREFER_WRITER_NP ,
results in the same behavior as setting the value to
.IR PTHREAD_RWLOCK_PREFER_READER_NP .
As long as a reader thread holds the lock the thread holding a 
write lock will be starved. Setting the kind value to
.IR PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP ,
allows the writer to run. However, the writer may not be
recursive as is implied by the name. See
http://sourceware.org/bugzilla/show_bug.cgi?id=7057
.SH CONFORMING TO
These functions are non-standard GNU extensions;
hence the suffix "_np" (non-portable) in the names.
.SH SEE ALSO
.BR pthreads (7)
Commit	Line	Data
88e15474 RS	1	.\"Copyright (c) 2010 Novell Inc., written by Robert Schweikert
	2	.\" <mtk.manpages@gmail.com>
	3	.\"
	4	.\" Permission is granted to make and distribute verbatim copies of this
	5	.\" manual provided the copyright notice and this permission notice are
	6	.\" preserved on all copies.
	7	.\"
	8	.\" Permission is granted to copy and distribute modified versions of this
	9	.\" manual under the conditions for verbatim copying, provided that the
	10	.\" entire resulting derived work is distributed under the terms of a
	11	.\" permission notice identical to this one.
	12	.\"
	13	.\" Since the Linux kernel and libraries are constantly changing, this
	14	.\" manual page may be incorrect or out-of-date. The author(s) assume no
	15	.\" responsibility for errors or omissions, or for damages resulting from
	16	.\" the use of the information contained herein. The author(s) may not
	17	.\" have taken the same level of care in the production of this manual,
	18	.\" which is licensed free of charge, as they might when working
	19	.\" professionally.
	20	.\"
	21	.\" Formatted or processed versions of this manual, if unaccompanied by
	22	.\" the source, must acknowledge the copyright and authors of this work.
	23	.\"
	24	.TH PTHREAD_RWLOCKATTR_SETKIND_NP 3 2010-06-09 "Linux Programmer's Manual"
	25	.SH NAME
	26	pthread_rwlockattr_setkind_np, pthread_rwlockattr_getkind_np \- set/get
	27	the read-write lock kind of the thread read-write lock attribute object
	28	.SH SYNOPSIS
	29	.nf
	30	.B #define _XOPEN_SOURCE 500
	31	.B #include <pthread.h>
	32
	33	.BI "int pthread_rwlockattr_setkind_np (pthread_rwlockattr_t *" attr ,
	34	.BI " int" pref);
	35	.BI "int pthread_rwlockattr_getkind_np (const pthread_rwlockattr_t *" attr ,
	36	.BI " int *" pref);
	37	.sp
	38	Compile and link with \fI\-pthread\fP.
	39	.SH DESCRIPTION
	40	The
	41	.BR pthread_rwlockattr_setkind_np ()
	42	function
	43	sets the kind of read-write lock of the
	44	thread read-write lock attribute object referred to by
	45	.I attr
	46	to the value specified with
	47	.IR pref .
	48	The argument
	49	.I pref
	50	may be set to
	51	.IR PTHREAD_RWLOCK_PREFER_READER_NP ,
	52	.IR PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP ,
	53	or
	54	.IR PTHREAD_RWLOCK_PREFER_WRITER_NP .
	55	The default lock setting is
	56	.IR PTHREAD_RWLOCK_PREFER_READER_NP .
	57	A thread may hold multiple read locks, i.e. read locks are recursive.
	58	According to The Single Unix Specification, the behavior is unspecified when a
	59	reader tries to place a lock, and there is no write lock but writers are
	60	waiting. Giving preference to the reader, as is set by default with the
	61	.IR PTHREAD_RWLOCK_PREFER_READER_NP value
	62	implies that the reader will receive the requested lock, even if
	63	a writer is waiting. As long as there are readers the writer will be
	64	starved. Setting the kind to
65	.IR PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP ,
66	avoids writer starvation as long as any read locking is not done in a
67	recursive fashion.
68
69	The
70	.BR pthread_rwlockattr_getkind_np ()
71	function
72	returns the value of the read-write lock attribute of the
73	thread read-write lock attribute object referred to by
74	.IR attr
75	in the pointer
76	.IR pref .
77	.SH RETURN VALUE
78	On success, these functions return 0;
79	on error,
80	.BR pthread_rwlockattr_setkind_np ()
81	returns a non-zero error number.
82	.SH ERRORS
83	.TP
84	.BR EINVAL
85	.I pref
86	is set to an unsupported value.
87	.SH BUGS
88	Setting the value read-write lock kind to
89	.IR PTHREAD_RWLOCK_PREFER_WRITER_NP ,
90	results in the same behavior as setting the value to
91	.IR PTHREAD_RWLOCK_PREFER_READER_NP .
92	As long as a reader thread holds the lock the thread holding a
93	write lock will be starved. Setting the kind value to
94	.IR PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP ,
95	allows the writer to run. However, the writer may not be
96	recursive as is implied by the name. See
97	http://sourceware.org/bugzilla/show_bug.cgi?id=7057
98	.SH CONFORMING TO
99	These functions are non-standard GNU extensions;
100	hence the suffix "_np" (non-portable) in the names.
101	.SH SEE ALSO
102	.BR pthreads (7)