Man page - pthread_rwlockattr_setkind_np(3)

Packages contains this manual

Available languages:

en fr ja ru ro

Manual

pthread_rwlockattr_setkind_np

NAME
LIBRARY
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
STANDARDS
HISTORY
SEE ALSO

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" 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 . This is ignored by glibc because the POSIX requirement to support recursive read locks would cause this option 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)