Section (3) pthread_rwlockattr_setkind_np
pthread_rwlockattr_setkind_np, pthread_rwlockattr_getkind_np — set/get the read-write lock kind of the thread read-write lock attribute object
||const pthread_rwlockattr_t *attr,|
Compile and link with
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:
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_NPwhich 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.
returns the value of the lock kind attribute of the
read-write lock attribute object referred to by
attr in the pointer
On success, these functions return 0. Given valid pointer
succeeds. On error,
pthread_rwlockattr_setkind_np() returns a
nonzero error number.
functions first appeared in glibc 2.1.
These functions are non-standard GNU extensions; hence the suffix _np (nonportable) in the names.
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