x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
pthread_rwlockattr_setkind_Library Functions Mpthread_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
LIBRARY
POSIX threads library (libpthread, -lpthread)
SYNOPSIS
#include <pthread.h>
int pthread_rwlockattr_setkind_np(pthread_rwlockattr_t *attr,
int pref);
int pthread_rwlockattr_getkind_np(
const pthread_rwlockattr_t *restrict attr,
int *restrict pref);
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" at-
tribute 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. This is ignored by glibc because the POSIX re-
quirement to support recursive read locks would cause this op-
tion to create trivial deadlocks; instead use
PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP which ensures the
application developer will not take recursive read locks thus
avoiding deadlocks.
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 nonzero error number.
ERRORS
EINVAL pref specifies an unsupported value.
STANDARDS
GNU; hence the suffix "_np" (nonportable) in the names.
HISTORY
glibc 2.1.
SEE ALSO
pthreads(7)
Linux man-pages 6.04 2023-03-30 pthread_rwlockattr_setkind_np(3)
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