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); |
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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.
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.
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/.
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