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.

Description: Invalid argument.

Description: rwlp or arg points to an illegal address.