pthread_rwlockattr_setkind_np, pthread_rwlockattr_getkind_np - set/get the
read-write lock kind of the thread read-write lock attribute object
int pthread_rwlockattr_setkind_np(pthread_rwlockattr_t *attr,
int pthread_rwlockattr_getkind_np(const pthread_rwlockattr_t *attr,
Compile and link with -pthread.
Feature Test Macro Requirements for glibc (see feature_test_macros
_XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE
() function sets the "lock
kind" attribute of the read-write lock attribute object referred to by
to the value specified in pref
. The argument pref
may be set to one of the following:
- 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
- Setting the lock kind to this avoids writer starvation as long as any read
locking is not done in a recursive fashion.
() function returns the value of the
lock kind attribute of the read-write lock attribute object referred to by
in the pointer pref
On success, these functions return 0. Given valid pointer arguments,
() always succeeds. On error,
() returns a nonzero error number.
- pref specifies an unsupported value.
() functions first appeared in glibc 2.1.
These functions are non-standard GNU extensions; hence the suffix
"_np" (nonportable) in the names.