Initialize a Read-Write Lock

Use rwlock_init(3C) to initialize the read-write lock pointed to by rwlp and to set the lock state to unlocked.

rwlock_init Syntax

#include <synch.h>  (or #include <thread.h>)

int rwlock_init(rwlock_t *rwlp, int type, void * 
arg);

type can be one of the following values:

• USYNC_PROCESS The read-write lock can be used to synchronize threads in this process and other processes. arg is ignored.

• USYNC_THREAD The read-write lock can be used to synchronize threads in this process only. arg is ignored.

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 the lock.

For POSIX threads, see pthread_rwlock_init Syntax .

Initializing Read-Write Locks With Intraprocess Scope

#include <thread.h> 
rwlock_t rwlp; 
int ret; 
/* to be used within this process only */ 
ret = rwlock_init(&rwlp, USYNC_THREAD, 0); 

Initializing Read-Write Locks With Interprocess Scope

#include <thread.h> 
rwlock_t rwlp; 
int ret; 
/* to be used among all processes */ 
ret = rwlock_init(&rwlp, USYNC_PROCESS, 0); 

rwlock_init Return Values

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.

EINVAL

Description:

Invalid argument.

EFAULT

Description:

rwlp or arg points to an illegal address.