void
callout_init(
callout_t *c
, u_int flags
)
void
callout_destroy(
callout_t *c
)
void
callout_reset(
callout_t *c
, int ticks
, void (*func)(void *)
, void *arg
)
void
callout_schedule(
callout_t *c
, int ticks
)
void
callout_setfunc(
callout_t *c
, void (*func)(void *)
, void *arg
)
bool
callout_stop(
callout_t *c
)
bool
callout_pending(
callout_t *c
)
bool
callout_expired(
callout_t *c
)
bool
callout_active(
callout_t *c
)
bool
callout_invoking(
callout_t *c
)
bool
callout_ack(
callout_t *c
)
hz
times per second.
The function is called at softclock interrupt level.
Clients of the
callout
facility are responsible for providing pre-allocated
callout structures, or
``handles''.
The
callout
facility replaces the historic
UNIX
functions
timeout()
and
untimeout(
).
The
callout_init()
function initializes the callout handle
c
for use.
No operations can be performed on the callout before it is initialized.
If the
flags
argument is
CALLOUT_MPSAFE
,
the handler will be called without getting the global kernel lock.
In this case it should only use functions that are multiprocessor
safe.
callout_destroy()
destroys the callout, preventing further use.
It is provided as a diagnostic facility intended to catch bugs.
To ensure future compatibility,
callout_destroy(
)
should always be called when the callout is no longer required (for instance,
when a device is being detached).
The
callout_reset()
function resets and starts the timer associated with the callout handle
c
.
When the timer expires after
ticks
/hz
seconds, the function specified by
func
will be called with the argument
arg
.
If the timer associated with the callout handle is already running,
the callout will simply be rescheduled to execute at the newly specified
time.
Once the timer is started, the callout handle is marked as
PENDING.
Once the timer expires,
the handle is marked as
EXPIRED
and
INVOKING,
and the
PENDING
status is cleared.
The
callout_setfunc()
function sets the function and argument of the callout handle
c
to
func
and
arg
respectively.
The callout handle must already be initialized.
If a callout will always be used with the same function and argument,
then
callout_setfunc()
used in conjunction with
callout_schedule(
)
is slightly more efficient than using
callout_reset(
).
The
callout_stop()
function stops the timer associated the callout handle
c
.
The
PENDING
and
EXPIRED
status for the callout handle is cleared.
It is safe to call
callout_stop()
on a callout handle that is not pending, so long as it is initialized.
callout_stop(
)
will return a non-zero value if the callout was
EXPIRED.
The
callout_pending()
function tests the
PENDING
status of the callout handle
c
.
A
PENDING
callout is one that has been started and whose function has not yet
been called.
Note that it is possible for a callout's timer to have expired without
its function being called if interrupt level has not dropped low enough
to let softclock interrupts through.
Note that it is only safe to test
PENDING
status when at softclock interrupt level or higher.
The
callout_expired()
function tests to see if the callout's timer has expired and its
function called.
The
callout_active()
function returns true if a timer has been started but not explicitly stopped,
even if it has already fired.
callout_active(
foo
)
is logically the same as
callout_pending(foo
)
||
callout_expired(foo
);
it is implemented as a separate function for compatibility with
FreeBSD
and for the special case of
TCP_TIMER_ISARMED().
Its use is not recommended.
The
callout_invoking()
function tests the
INVOKING
status of the callout handle
c
.
This flag is set just before a callout's function is being called.
Since the priority level is lowered prior to invocation of the
callout function, other pending higher-priority code may run before
the callout function is allowed to run.
This may create a race condition if this higher-priority code
deallocates storage containing one or more callout structures whose
callout functions are about to be run.
In such cases, one technique to prevent references to deallocated
storage would be to test whether any callout functions are in the
INVOKING
state using
callout_invoking(),
and if so, to mark the data structure and defer storage
deallocation until the callout function is allowed to run.
For this handshake protocol to work, the callout function will
have to use the
callout_ack(
)
function to clear this flag.
The
callout_ack()
function clears the
INVOKING
state in the callout handle
c
.
This is used in situations where it is necessary to protect against
the race condition described under
callout_invoking().