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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"
       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_PRE-
              FER_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 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"
       (non-portable) in the names.
BUGS
       Setting  the  value  read-write  lock   kind   to   PTHREAD_RWLOCK_PRE-
       FER_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  writ-
       ers to run, but, as the name implies a writer may not lock recursively.
SEE ALSO
       pthreads(7)
COLOPHON
       This  page  is  part of release 4.15 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         2018-02-02  PTHREAD_RWLOCKATTR_SETKIND_NP(3)