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pthread_rwlockattr_setkind_np(3) [linux man page]

PTHREAD_RWLOCKATTR_SETKIND_NP(3)			     Library Functions Manual				  PTHREAD_RWLOCKATTR_SETKIND_NP(3)

NAME
pthread_rwlockattr_setkind_np, pthread_rwlockattr_getkind_np - set/get the read-write lock kind of the thread read-write lock attribute object SYNOPSIS
#include <pthread.h> 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)): 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 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 Speci- fication, the behavior is unspecified when a reader tries to place a lock, and there is no write lock but writers are waiting. Giv- ing 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. But see BUGS. 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 non-zero error number. ERRORS
EINVAL pref specifies an unsupported value. BUGS
Setting the value read-write lock kind to PTHREAD_RWLOCK_PREFER_WRITER_NP results in the same behavior as setting the value to PTHREAD_RWLOCK_PREFER_READER_NP. As long as a reader thread holds the lock, the thread holding a write lock will be starved. Setting the lock kind to PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP allows writers to run, but, as the name implies a writer may not lock recur- sively. VERSIONS
The pthread_rwlockattr_getkind_np() and pthread_rwlockattr_setkind_np() functions first appeared in glibc 2.1. CONFORMING TO
These functions are non-standard GNU extensions; hence the suffix "_np" (non-portable) in the names. SEE ALSO
pthreads(7) Linux Programmer's Manual 2014-10-15 PTHREAD_RWLOCKATTR_SETKIND_NP(3)

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pthread_rwlock_wrlock(3T)												 pthread_rwlock_wrlock(3T)

NAME
pthread_rwlock_wrlock(), pthread_rwlock_trywrlock() - lock or attempt to lock a read-write lock for writing SYNOPSIS
PARAMETERS
rwlock Pointer to the read-write lock to be locked for writing. DESCRIPTION
The function applies a write lock to the read-write lock object referenced by rwlock. The calling thread acquires the write lock if no other thread (reader or writer) holds the read-write lock rwlock. Otherwise, the thread blocks (that is, it does not return from the call) until it can acquire the lock. Results are undefined if the calling thread holds the read-write lock (whether a read or a write lock) at the time the call is made. The function applies a write lock as in the function with the exception that the function fails if any thread currently holds rwlock (for reading or writing). Results are undefined if any of these functions are called with an uninitialized read-write lock. If a signal is delivered to a thread waiting for a read-write lock, upon return from the signal handler, the thread shall resume waiting for the read-write lock as if it was not interrupted. RETURN VALUE
Upon successful completion, and return zero. Otherwise, an error number is returned to indicate the error (the variable is not set). ERRORS
If any of the following occur, the function returns the corresponding error number: [EBUSY] The read-write lock rwlock could not be acquired for writing because it was already locked for reading or writing. For each of the following conditions, if the condition is detected, the and functions return the corresponding error number: [EINVAL] The value specified by rwlock does not refer to an initialized read-write lock. [EDEADLK] The current thread already owns the read-write lock for reading or writing. AUTHOR
and were developed by X/Open. SEE ALSO
pthread_rwlock_init(3T), pthread_rwlock_destroy(3T), pthread_rwlock_tryrdlock(3T), pthread_rwlock_rdlock(3T), pthread_rwlock_unlock(3T). STANDARDS CONFORMANCE
Pthread Library pthread_rwlock_wrlock(3T)

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