pthread_rwlockattr_getkind_np(3)

1PTHREAD_RWLOCKATTR_SETKIND_NLPi(b3r)ary Functions MaPnTuHaRlEAD_RWLOCKATTR_SETKIND_NP(3)
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NAME

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

10       #include <pthread.h>
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12       int pthread_rwlockattr_setkind_np(pthread_rwlockattr_t *attr,
13                              int pref);
14       int pthread_rwlockattr_getkind_np(
15                              const pthread_rwlockattr_t *restrict attr,
16                              int *restrict pref);
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18       Compile and link with -pthread.
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20   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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22       pthread_rwlockattr_setkind_np(), pthread_rwlockattr_getkind_np():
23           _XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE >= 200809L
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DESCRIPTION

26       The pthread_rwlockattr_setkind_np() function sets the "lock  kind"  at‐
27       tribute  of the read-write lock attribute object referred to by attr to
28       the value specified in pref.  The argument pref may be set  to  one  of
29       the following:
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31       PTHREAD_RWLOCK_PREFER_READER_NP
32              This  is  the  default.   A thread may hold multiple read locks;
33              that is, read locks are recursive.  According to The Single Unix
34              Specification,  the  behavior is unspecified when a reader tries
35              to place a lock, and there is no  write  lock  but  writers  are
36              waiting.   Giving  preference  to  the  reader,  as  is  set  by
37              PTHREAD_RWLOCK_PREFER_READER_NP, implies that  the  reader  will
38              receive  the  requested  lock,  even if a writer is waiting.  As
39              long as there are readers, the writer will be starved.
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41       PTHREAD_RWLOCK_PREFER_WRITER_NP
42              This is intended as the write lock analog of PTHREAD_RWLOCK_PRE‐
43              FER_READER_NP.   This  is ignored by glibc because the POSIX re‐
44              quirement to support recursive read locks would cause  this  op‐
45              tion     to    create    trivial    deadlocks;    instead    use
46              PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP which  ensures  the
47              application  developer  will  not take recursive read locks thus
48              avoiding deadlocks.
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50       PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP
51              Setting the lock kind to this avoids writer starvation  as  long
52              as any read locking is not done in a recursive fashion.
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54       The  pthread_rwlockattr_getkind_np()  function returns the value of the
55       lock kind attribute of the read-write lock attribute object referred to
56       by attr in the pointer pref.
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RETURN VALUE

59       On  success,  these functions return 0.  Given valid pointer arguments,
60       pthread_rwlockattr_getkind_np()    always    succeeds.     On    error,
61       pthread_rwlockattr_setkind_np() returns a nonzero error number.
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ERRORS

64       EINVAL pref specifies an unsupported value.
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VERSIONS

67       The pthread_rwlockattr_getkind_np() and pthread_rwlockattr_setkind_np()
68       functions first appeared in glibc 2.1.
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CONFORMING TO

71       These functions are non-standard GNU extensions; hence the suffix "_np"
72       (nonportable) in the names.
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COLOPHON

78       This  page  is  part of release 5.13 of the Linux man-pages project.  A
79       description of the project, information about reporting bugs,  and  the
80       latest     version     of     this    page,    can    be    found    at
81       https://www.kernel.org/doc/man-pages/.
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85Linux Programmer's Manual         2021-03-22  PTHREAD_RWLOCKATTR_SETKIND_NP(3)