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   pthread_rwlockattr_getkind_np    ( 3 )

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Имя (Name)

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

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Синопсис (Synopsis)

#include <pthread.h>

       int pthread_rwlockattr_setkind_np(pthread_rwlockattr_t *attr,
                              int pref);
       int pthread_rwlockattr_getkind_np(
                              const pthread_rwlockattr_t *restrict attr,
                              int *restrict 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

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Описание (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.  This is ignored by glibc
              because the POSIX requirement to support recursive read
              locks would cause this option 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.

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Возвращаемое значение (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.

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Ошибки (Error)

EINVAL pref specifies an unsupported value.

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Версии (Versions)

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

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Стандарты (Conforming to)

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

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Смотри также (See also)

pthreads(7)

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