pthread_rwlockattr_getkind_np

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

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"  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 writer 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.

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"
       (nonportable) in the names.

SEE ALSO
       pthreads(7)

COLOPHON
       This  page  is  part of release 5.05 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         2019-03-06  PTHREAD_RWLOCKATTR_SETKIND_NP(3)