Name
pthread_rwlockattr_setkind_np, pthread_rwlockattr_getkind_np - set/get the read-write lock kind of the thread read-write lock attribute objectLibrary
POSIX threads library ( libpthread ", " -lpthread )Synopsis
#include <pthread.h> int pthread_rwlockattr_setkind_np(pthread_rwlockattr_t * attr ,Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
int pref );
int pthread_rwlockattr_getkind_np( const pthread_rwlockattr_t *restrict attr ,
int *restrict pref );
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 inpref
. 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
.
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.
Standards
GNU; hence the suffix "_np" (nonportable) in the names.History
glibc 2.1.See Also
- pthreads(7)