Obtain a write lock on @rw_lock. If another thread currently holds
a read or write lock on @rw_lock, the current thread will block
until all other threads have dropped their locks on @rw_lock.
Calling g_rw_lock_writer_lock() while the current thread already
owns a read or write lock on @rw_lock leads to undefined behaviour.
Obtain a write lock on @rw_lock. If another thread currently holds a read or write lock on @rw_lock, the current thread will block until all other threads have dropped their locks on @rw_lock.
Calling g_rw_lock_writer_lock() while the current thread already owns a read or write lock on @rw_lock leads to undefined behaviour.