rwlock_init(SYNCH)

rwlock_init -- initialize a reader-writer lock

Synopsis

   cc [options] -Kthread file
   
   #include <synch.h>
   

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

Description

rwlock_init initializes the reader-writer lock pointed to by rwlock to be of type type and in the unlocked state. Once initialized, the lock can be used any number of times without being re-initialized.

Parameters

rwlock: pointer to reader-writer lock to be initialized
type: USYNC_THREAD or USYNC_PROCESS
arg: NULL (reserved for future use)

rwlock parameter

rwlock points to the reader-writer lock to be initialized.

type parameter

type can be set to one of the following values:

USYNC_THREAD: initialize the reader-writer lock for threads within the current process
USYNC_PROCESS: initialize the reader-writer lock for threads across processes

arg parameter

arg should be set to NULL. It is not currently used, but is reserved for future use.

Static reader-Writer initialization

In this implementation, a reader-writer lock can be initialized statically if its storage is zero-filled. In this case, the reader-writer lock is of type USYNC_THREAD, and rwlock_init need not be called.

Return values

rwlock_init returns zero for success and an error number for failure.

Errors

If the following condition is detected, the contents of rwlock are not changed, and rwlock_init returns the corresponding value:

EINVAL: Invalid type argument specified.

Warnings

rwlock_init does not examine the rwlock argument before initializing it. If rwlock_init is called more than once for the same reader-writer lock, it will overwrite its state. It is the user's responsibility to ensure that rwlock_init is only called once for each reader-writer lock.

Operations on locks initialized with rwlock_init are not recursive--a thread can deadlock if it attempts to reacquire a reader-writer lock that it already has acquired.

References

Intro(SYNCH), rwlock(SYNCH), rwlock_destroy(SYNCH), rw_rdlock(SYNCH), rw_tryrdlock(SYNCH), rw_trywrlock(SYNCH), rw_unlock(SYNCH), rw_wrlock(SYNCH)