'\" te
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.TH DDI_PERIODIC_DELETE 9F "Feb 12, 2014"
.SH NAME
ddi_periodic_delete \- cancel periodic function invocation requests
.SH SYNOPSIS
.nf
#include <sys/dditypes.h>
#include <sys/sunddi.h>

\fBvoid\fR \fBddi_periodic_delete\fR(\fBddi_periodic_t\fR \fIrequest\fR\fB);\fR
.fi

.SH INTERFACE LEVEL
illumos DDI specific (illumos DDI)
.SH PARAMETERS
.ne 2
.na
\fB\fIrequest\fR\fR
.ad
.RS 7n
\fBddi_periodic_t\fR opaque value returned by \fBddi_periodic_add\fR(9F)
.RE

.SH DESCRIPTION
The \fBddi_periodic_delete()\fR function cancels a periodic invocation request
previously established with \fBddi_periodic_add\fR(9F).
.sp
.LP
It is not possible to cancel a periodic invocation request from within the
periodic callback itself; to do so is a programming error that will panic the
system.  Instead, requests must be cancelled from some other user or kernel
context routine, such as the \fBdetach\fR(9E) entry point of a module.
.sp
.LP
If the callback function is already executing (for instance, on another CPU)
when the request is cancelled, \fBddi_periodic_delete()\fR will block until
it finishes executing and is completely unregistered.  Because of this, locks
acquired by the callback function must not be held across the call to
\fBddi_periodic_delete()\fR or a deadlock may result.
.sp
.LP
The callback will not be invoked again after the call to
\fBddi_periodic_delete()\fR returns.
.SH CONTEXT
The \fBddi_periodic_delete()\fR function may be called from user or kernel
context.
.SH EXAMPLES
\fBExample 1 \fRCancelling a periodic invocation request
.sp
.LP
In the following example, the device driver cancels the request
by calling \fBddi_periodic_delete()\fR and passing the opaque \fIrequest\fR
identifier returned by a previous call to \fBddi_periodic_add\fR(9F).

.sp
.in +2
.nf
/*
 * Stop the periodic timer.
 */
static void
stop_periodic_timer(struct my_state *statep)
{
        ddi_periodic_delete(statep->periodic_id);
        mutex_destroy(&statep->lock);
}

static void
start_periodic_timer(struct my_state *statep)
{
        hrtime_t interval = CHECK_INTERVAL;

        mutex_init(&statep->lock, NULL, MUTEX_DRIVER, DDI_IPL_0);

        /*
         * Register my_callback which is invoked periodically
         * in CHECK_INTERVAL in kernel context.
         */
        statep->periodic_id = ddi_periodic_add(my_periodic_func,
            statep, interval, DDI_IPL_0);
}

static void
my_periodic_func(void *arg)
{
        /*
         * This handler is invoked periodically.
         */
        struct my_state *statep = (struct my_state *)arg;

        mutex_enter(&statep->lock);
        if (load_unbalanced(statep)) {
                balance_tasks(statep);
        }
        mutex_exit(&statep->lock);
}
.fi
.in -2

.SH SEE ALSO
.BR cv_timedwait (9F),
.BR ddi_intr_get_pri (9F),
.BR ddi_periodic_add (9F),
.BR qtimeout (9F),
.BR quntimeout (9F),
.BR timeout (9F),
.BR untimeout (9F)
.SH NOTES
Historically this interface was advertised as safe for use from within the
periodic callback function.  In order to ensure the correct operation of the
system, and as reflected in the documentation above, this unlikely (and
unsafe) usage pattern is no longer allowed.