NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | BUGS | SEE ALSO | COLOPHON

PTHREAD_RWLOCKATTR_SETKIND_NP(3)y Functions ManualD_RWLOCKATTR_SETKIND_NP(3)

NAME         top

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

SYNOPSIS         top

       #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         top

       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         top

       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         top

       EINVAL pref specifies an unsupported value.

VERSIONS         top

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

CONFORMING TO         top

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

BUGS         top

       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.

SEE ALSO         top

       pthreads(7)

COLOPHON         top

       This page is part of release 4.10 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)