# pthread_rwlock_trywrlock

## PROLOG



           This manual page is part of the POSIX Programmer's Manual.  The
           Linux implementation of this interface may differ (consult the
           corresponding Linux manual page for details of Linux behavior), or
           the interface may not be implemented on Linux.
    


## NAME



           pthread_rwlock_trywrlock, pthread_rwlock_wrlock — lock a read-
           write lock object for writing
    


## SYNOPSIS



           #include <pthread.h>
    
           int pthread_rwlock_trywrlock(pthread_rwlock_t *_rwlock_);
           int pthread_rwlock_wrlock(pthread_rwlock_t *_rwlock_);
    


## DESCRIPTION



           The _pthread_rwlock_trywrlock_() function shall apply a write lock
           like the _pthread_rwlock_wrlock_() function, with the exception that
           the function shall fail if any thread currently holds _rwlock_ (for
           reading or writing).
    
           The _pthread_rwlock_wrlock_() function shall apply a write lock to
           the read-write lock referenced by _rwlock_.  The calling thread
           shall acquire the write lock if no thread (reader or writer) holds
           the read-write lock _rwlock_.  Otherwise, if another thread holds
           the read-write lock _rwlock_ , the calling thread shall block until
           it can acquire the lock.  If a deadlock condition occurs or the
           calling thread already owns the read-write lock for writing or
           reading, the call shall either deadlock or return **[EDEADLK]**.
    
           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
           for writing, upon return from the signal handler the thread
           resumes waiting for the read-write lock for writing as if it was
           not interrupted.
    


## RETURN VALUE



           The _pthread_rwlock_trywrlock_() function shall return zero if the
           lock for writing on the read-write lock object referenced by
           _rwlock_ is acquired. Otherwise, an error number shall be returned
           to indicate the error.
    
           If successful, the _pthread_rwlock_wrlock_() function shall return
           zero; otherwise, an error number shall be returned to indicate the
           error.
    


## ERRORS



           The _pthread_rwlock_trywrlock_() function shall fail if:
    
           **EBUSY** The read-write lock could not be acquired for writing
                  because it was already locked for reading or writing.
    
           The _pthread_rwlock_wrlock_() function may fail if:
    
           **EDEADLK**
                  A deadlock condition was detected or the current thread
                  already owns the read-write lock for writing or reading.
    
           These functions shall not return an error code of **[EINTR]**.
    
           _The following sections are informative._
    


## EXAMPLES



           None.
    


## APPLICATION USAGE



           Applications using these functions may be subject to priority
           inversion, as discussed in the Base Definitions volume of
           POSIX.1‐2017, _Section 3.291_ , _Priority Inversion_.
    


## RATIONALE



           If an implementation detects that the value specified by the
           _rwlock_ argument to _pthread_rwlock_trywrlock_() or
           _pthread_rwlock_wrlock_() does not refer to an initialized read-
           write lock object, it is recommended that the function should fail
           and report an **[EINVAL]** error.
    


## FUTURE DIRECTIONS



           None.
    


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