PTHREAD_RWLOCKATTR_SETKIND_NP(3)PTHREAD_RWLOCKATTR_SETKIND_NP(3)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);
Compile and link with -pthread.
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
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_PRE‐
FER_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.
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.
BUGS
Setting the value read-write lock kind to PTHREAD_RWLOCK_PRE‐
FER_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 writ‐
ers to run, but, as the name implies a writer may not lock recursively.
SEE ALSOpthreads(7)COLOPHON
This page is part of release 4.14 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/.
Linux Programmer's Manual 2016-10-08 PTHREAD_RWLOCKATTR_SETKIND_NP(3)
