Name

pthread_rwlockattr_setkind_np, pthread_rwlockattr_getkind_np — set/get the read-write lock kind of the thread read-write lock attribute object

Synopsis

        #include <pthread.h>
int pthread_rwlockattr_setkind_np( pthread_rwlockattr_t *attr,
  int pref);
 
int pthread_rwlockattr_getkind_np( const pthread_rwlockattr_t *attr,
  int *pref);
 
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
pthread_rwlockattr_setkind_np(), pthread_rwlockattr_getkind_np():
_XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE >= 200809L
[Note] Note

Compile and link with −pthread.

DESCRIPTION

The pthread_rwlockattr_setkind_np() function sets the "lock kind" attribute of the read-write lock attribute object referred to by attr to the value specified in pref. The argument pref may be set to one of the following:

PTHREAD_RWLOCK_PREFER_READER_NP

This is the default. A thread may hold multiple read locks; that is, 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 PTHREAD_RWLOCK_PREFER_READER_NP, 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.

PTHREAD_RWLOCK_PREFER_WRITER_NP

This is intended as the write lock analog of PTHREAD_RWLOCK_PREFER_READER_NP. But see BUGS.

PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP

Setting the lock kind to this avoids writer starvation as long as any read locking is not done in a recursive fashion.

The pthread_rwlockattr_getkind_np() function returns the value of the lock kind attribute of the read-write lock attribute object referred to by attr in the pointer pref.

RETURN VALUE

On success, these functions return 0. Given valid pointer arguments, pthread_rwlockattr_getkind_np() always succeeds. On error, pthread_rwlockattr_setkind_np() returns a non-zero error number.

ERRORS

EINVAL

pref specifies an unsupported value.

BUGS

Setting the value read-write lock kind to PTHREAD_RWLOCK_PREFER_WRITER_NP results in the same behavior as setting the value to 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 lock kind to PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP allows writers to run, but, as the name implies a writer may not lock recursively.

VERSIONS

The pthread_rwlockattr_getkind_np() and pthread_rwlockattr_setkind_np() functions first appeared in glibc 2.1.

CONFORMING TO

These functions are non-standard GNU extensions; hence the suffix "_np" (non-portable) in the names.

SEE ALSO

pthreads(7)

COLOPHON

This page is part of release 4.07 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man−pages/.


 Copyright (c) 2010 Novell Inc., written by Robert Schweikert

%%%LICENSE_START(VERBATIM)
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.
%%%LICENSE_END