acquire a read/write lock in read mode
pl_t RW_RDLOCK(rwlock_t *lockp, pl_t pl);
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.
Pointer to the read/write lock to be acquired.
The interrupt priority level to be set while the lock is held
by the caller.
Upon acquiring the lock,
RW_RDLOCK returns the previous interrupt priority
level (plbase - plhi).
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
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
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
in order to avoid deadlock.
5, 5mp, 6, 6mp, 7, 7mp, 7.1, 7.1mp, 8, 8mp
``Spin locks (DDI)'' in HDK Technical Reference
19 June 2005
© 2005 The SCO Group, Inc. All rights reserved.
OpenServer 6 and UnixWare (SVR5) HDK - June 2005