#include <pthread.h> int pthread_rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr); pthread_rwlock_t rwlock = PTHREAD_RWLOCK_INITIALIZER;
Use pthread_rwlock_init(3T) to initialize the read-write lock referenced by rwlock with the attributes referenced by attr. If attr is NULL, the default read-write lock attributes are used; the effect is the same as passing the address of a default read-write lock attributes object. Once initialized, the lock can be used any number of times without being re-initialized. Upon successful initialization, the state of the read-write lock becomes initialized and unlocked. Results are undefined if pthread_rwlock_init() is called specifying an already initialized read-write lock. Results are undefined if a read-write lock is used without first being initialized. (For Solaris threads, see "rwlock_init(3T)".)
In cases where default read-write lock attributes are appropriate, the macro PTHREAD_RWLOCK_INITIALIZER can be used to initialize read-write locks that are statically allocated. The effect is equivalent to dynamic initialization by a call to pthread_rwlock_init() with the parameter attr specified as NULL, except that no error checks are performed.
If successful, pthread_rwlock_init() returns zero. Otherwise, an error number is returned to indicate the error.
If pthread_rwlock_init() fails, rwlock is not initialized and the contents of rwlock are undefined.