SVR5

RW_RDLOCK(D3)

RW_RDLOCK -- acquire a read/write lock in read mode

Synopsis

   #include <sys/types.h>
   #include <sys/ksynch.h>
   #include <sys/ddi.h>
   
   pl_t RW_RDLOCK(rwlock_t *lockp, pl_t pl);

Description

RW_RDLOCK sets the interrupt priority level in accordance with the value specified by pl (if required by the implementation) and acquires the lock specified by lockp in read mode. If the lock cannot be acquired immediately in read mode, the caller will wait until the lock is available in read mode. (A read/write lock is available in read mode when the lock is not held by any context or when the lock is held by one or more readers and there are no waiting writers). It is implementation defined whether the caller will block during the wait. Some implementations may cause the caller to spin for the duration of the wait, while on others the caller may block at some point.

Arguments

lockp: Pointer to the read/write lock to be acquired.
pl: The interrupt priority level to be set while the lock is held by the caller.

Return values

Upon acquiring the lock, RW_RDLOCK returns the previous interrupt priority level (plbase - plhi).

Usage

Because some implementations require that interrupts that might attempt to acquire the lock be blocked on the processor on which the lock is held, portable drivers must specify a pl value that is sufficient to block out any interrupt handler that might attempt to acquire this lock. See the description of the min_pl argument to RW_ALLOC(D3) for additional discussion and a list of the valid values for pl. Implementations which do not require that the interrupt priority level be raised during lock acquisition may choose to ignore this argument.

When called from interrupt level, the pl argument must not specify a priority level below the level at which the interrupt handler is running.

Context and synchronization

Non-blockable, interrupt, user, or blockable context.

Read/write locks are not recursive. A call to RW_RDLOCK attempting to acquire a lock that is currently held by the calling context may result in deadlock.

Calls to RW_RDLOCK should honor the ordering defined by the lock hierarchy(D5) in order to avoid deadlock.

Hardware applicability

All

Version applicability

ddi: 5, 5mp, 6, 6mp, 7, 7mp, 7.1, 7.1mp, 8, 8mp

References

hierarchy(D5), RW_ALLOC(D3), RW_DEALLOC(D3), RW_TRYRDLOCK(D3), RW_TRYWRLOCK(D3), RW_UNLOCK(D3), RW_WRLOCK(D3)

``Spin locks (DDI)'' in HDK Technical Reference