#include <synch.h> (or #include <thread.h>) int rwlock_init(rwlock_t *rwlp, int type, void * arg);
Use rwlock_init(3THR) to initialize the read-write lock pointed to by rwlp and to set the lock state to unlocked. type can be one of the following (note that arg is currently ignored). (For POSIX threads, see pthread_rwlock_init(3THR).)
Multiple threads must not initialize the same read-write lock simultaneously. Read-write locks can also be initialized by allocation in zeroed memory, in which case a type of USYNC_THREAD is assumed. A read-write lock must not be reinitialized while other threads might be using it.
#include <thread.h> rwlock_t rwlp; int ret; /* to be used within this process only */ ret = rwlock_init(&rwlp, USYNC_THREAD, 0);
#include <thread.h> rwlock_t rwlp; int ret; /* to be used among all processes */ ret = rwlock_init(&rwlp, USYNC_PROCESS, 0);
rwlock_init() returns zero after completing successfully. Any other return value indicates that an error occurred. When any of the following conditions occurs, the function fails and returns the corresponding value.