| 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. |
| EINVAL | pref specifies an unsupported value. |
NAME
pthread_rwlockattr_setkind_np, pthread_rwlockattr_getkind_np - set/get the read-write lock kind of the thread read-write lock attribute object
LIBRARY
POSIX threads library (libpthread, -lpthread)
SYNOPSIS
#include <pthread.h>int pthread_rwlockattr_setkind_np(pthread_rwlockattr_t *\nattr\n,\n
\n int \npref\n);\n
\nint pthread_rwlockattr_getkind_np(\n
\n const pthread_rwlockattr_t *restrict \nattr\n,\n
\n int *restrict \npref\n);pthread_rwlockattr_setkind_np(), pthread_rwlockattr_getkind_np():
\n
_XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE >= 200809LDESCRIPTION
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.
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)