timeout

- execute a function after a specified length of time

Synopsis

#include <sys/types.h>
#include <sys/conf.h>

timeout_id_t timeout(void (* func)(void *), void *arg, 
     clock_t  ticks);

Interface Level

Architecture independent level 1 (DDI/DKI).

Parameters

func

Kernel function to invoke when the time increment expires.

arg

Argument to the function.

ticks

Number of clock ticks to wait before the function is called. Use drv_usectohz(9F) to convert microseconds to clock ticks.

Description

The timeout() function schedules the specified function to be called after a specified time interval. The exact time interval over which the timeout takes effect cannot be guaranteed, but the value given is a close approximation.

The function called by timeout() must adhere to the same restrictions as a driver soft interrupt handler.

The delay(9F) function calls timeout(). Because timeout() is subject to priority inversion, drivers waiting on behalf of processes with real-time constraints should use cv_timedwait(9F) rather than delay().

Return Values

The timeout() function returns an opaque non-zero timeout identifier that can be passed to untimeout(9F) to cancel the request.

Context

The timeout() function can be called from user, interrupt, or kernel context.

Examples

Example 1 Using timeout()

In the following example, the device driver has issued an IO request and is waiting for the device to respond. If the device does not respond within 5 seconds, the device driver will print out an error message to the console.

static void
xxtimeout_handler(void *arg)
{
        struct xxstate *xsp = (struct xxstate *)arg;
        mutex_enter(&xsp->lock);
        cv_signal(&xsp->cv);
        xsp->flags |= TIMED_OUT;
        mutex_exit(&xsp->lock);
        xsp->timeout_id = 0;
}
static uint_t
xxintr(caddr_t arg)
{
        struct xxstate *xsp = (struct xxstate *)arg;
         .
         .
         .
        mutex_enter(&xsp->lock);
        /* Service interrupt */
        cv_signal(&xsp->cv);
        mutex_exit(&xsp->lock);
        if (xsp->timeout_id != 0) {
                (void) untimeout(xsp->timeout_id);
                xsp->timeout_id = 0;
        }
        return(DDI_INTR_CLAIMED);
}
static void
xxcheckcond(struct xxstate *xsp)
{
         .
         .
         .
        xsp->timeout_id = timeout(xxtimeout_handler,
            xsp, (5 * drv_usectohz(1000000)));
        mutex_enter(&xsp->lock);
        while (/* Waiting for interrupt  or timeout*/)
                cv_wait(&xsp->cv, &xsp->lock);
        if (xsp->flags & TIMED_OUT)
                cmn_err(CE_WARN, "Device not responding");
         .
         .
         .
        mutex_exit(&xsp->lock);
         .
         .
         .
}   

See Also

bufcall(9F), cv_timedwait(9F), ddi_in_panic(9F), delay(9F), drv_usectohz(9F), untimeout(9F)

Writing Device Drivers