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)):
_XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE >= 200809L
- 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.
- 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 writer 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.
- Setting the lock kind to this avoids writer starvation as long as any read locking is not done in a recursive fashion.
- pref specifies an unsupported value.