January 30, 2003 PTHREAD_RWLOCK_INIT 3

### NAME

pthread_rwlock_init - initialize a read/write lock

### LIBRARY

POSIX Thread Library (libpthread, -lpthread)

### SYNOPSIS

```int` pthread_rwlock_init(```pthread_rwlock_t * restrict lock``, const pthread_rwlockattr_t * restrict attr`)

### DESCRIPTION

The pthread_rwlock_init(``) function is used to initialize a read/write lock, with attributes specified by ```attr`. If ```attr` is NULL, the default read/write lock attributes are used.

The results of calling pthread_rwlock_init(``) with an already initialized lock are undefined.

### RETURN VALUES

If successful, the pthread_rwlock_init(``) function will return zero. Otherwise an error number will be returned to indicate the error.

### ERRORS

The pthread_rwlock_init(``) function shall fail if:

[```EAGAIN`]
  The system lacks the resources to initialize another read-write lock.

[```ENOMEM`]
  Insufficient memory exists to initialize the read-write lock.

The pthread_rwlock_init(``) function may fail if:

[```EBUSY`]
  The system has detected an attempt to re-initialize the object referenced by ```lock`, a previously initialized but not yet destroyed read/write lock.

[```EINVAL`]
  The value specified by ```attr` is invalid.

### SEE ALSO

pthread_rwlock_destroy(3), pthread_rwlock_rdlock(3), pthread_rwlock_unlock(3), pthread_rwlock_wrlock(3)

### STANDARDS

pthread_rwlock_init(``) conforms to ISO/IEC 9945-1:1996 (``POSIX.1'') .

### BUGS

The PTHREAD_PROCESS_SHARED attribute is not supported.