taskq(9F) Kernel Functions for Drivers taskq(9F)NAME
taskq, ddi_taskq_create, ddi_taskq_destroy, ddi_taskq_dispatch,
ddi_taskq_wait, ddi_taskq_suspend, taskq_suspended, ddi_taskq_resume -
Kernel task queue operations
SYNOPSIS
#include <sys/sunddi.h>
ddi_taskq_t *ddi_taskq_create(dev_info_t *dip, const char *name, int
nthreads, pri_t pri, uint_t cflags);
void ddi_taskq_destroy(ddi_taskq_t *tq);
int ddi_taskq_dispatch(ddi_taskq_t *tq, void (* func)(void *), void
*arg, uint_t dflags);
void ddi_taskq_wait(ddi_taskq_t *tq);
void ddi_taskq_suspend(ddi_taskq_t *tq);
boolean_t ddi_taskq_suspended(ddi_taskq_t *tq);
void ddi_taskq_resume(ddi_taskq_t *tq);
INTERFACE LEVEL
Solaris DDI specific (Solaris DDI)
PARAMETERS
dip
Pointer to the device's dev_info structure. May be NULL for kernel
modules that do not have an associated dev_info structure.
name
Descriptive string. Only alphanumeric characters can be used
in name and spaces are not allowed. The name should be unique.
nthreads
Number of threads servicing the task queue. Note that the request
ordering is guaranteed (tasks are processed in the order scheduled)
if the taskq is created with a single servicing thread.
pri
Priority of threads servicing the task queue. Drivers and modules
should specify TASKQ_DEFAULTPRI.
cflags
Should pass 0 as flags.
func
Callback function to call.
arg
Argument to the callback function.
dflags
Possible dflags are:
DDI_SLEEP Allow sleeping (blocking) until memory is avail‐
able.
DDI_NOSLEEP Return DDI_FAILURE immediately if memory is not
available.
tq
Pointer to a task queue (ddi_taskq_t *).
tp
Pointer to a thread structure.
DESCRIPTION
A kernel task queue is a mechanism for general-purpose asynchronous
task scheduling that enables tasks to be performed at a later time by
another thread. There are several reasons why you may utilize asynchro‐
nous task scheduling:
1. You have a task that isn't time-critical, but a current code path
that is.
2. You have a task that may require grabbing locks that a thread
already holds.
3. You have a task that needs to block (for example, to wait for mem‐
ory), but a have a thread that cannot block in its current context.
4. You have a code path that can't complete because of a specific con‐
dition, but also can't sleep or fail. In this case, the task is
immediately queued and then is executed after the condition disap‐
pears.
5.
A task queue is just a simple way to launch multiple tasks in par‐
allel.
A task queue consists of a list of tasks, together with one or more
threads to service the list. If a task queue has a single service
thread, all tasks are guaranteed to execute in the order they were dis‐
patched. Otherwise they can be executed in any order. Note that since
tasks are placed on a list, execution of one task and should not depend
on the execution of another task or a deadlock may occur. A taskq cre‐
ated with a single servicing thread guarantees that all the tasks are
serviced in the order in which they are scheduled.
The ddi_taskq_create() function creates a task queue instance.
The ddi_taskq_dispatch() function places taskq on the list for later
execution. The dflag argument specifies whether it is allowed sleep
waiting for memory. DDI_SLEEP dispatches can sleep and are guaranteed
to succeed. DDI_NOSLEEP dispatches are guaranteed not to sleep but may
fail (return DDI_FAILURE) if resources are not available.
The ddi_taskq_destroy() function waits for any scheduled tasks to com‐
plete, then destroys the taskq. The caller should guarantee that no new
tasks are scheduled for the closing taskq.
The ddi_taskq_wait() function waits for all previously scheduled tasks
to complete. Note that this function does not stop any new task dis‐
patches.
The ddi_taskq_suspend() function suspends all task execution until
ddi_taskq_resume() is called. Although ddi_taskq_suspend() attempts to
suspend pending tasks, there are no guarantees that they will be sus‐
pended. The only guarantee is that all tasks dispatched after
ddi_taskq_suspend() will not be executed. Because it will trigger a
deadlock, the ddi_taskq_suspend() function should never be called by a
task executing on a taskq.
The ddi_taskq_suspended() function returns B_TRUE if taskq is sus‐
pended, and B_FALSE otherwise. It is intended to ASSERT that the task
queue is suspended.
The ddi_taskq_resume() function resumes task queue execution.
RETURN VALUES
The ddi_taskq_create() function creates an opaque handle that is used
for all other taskq operations. It returns a taskq pointer on success
and NULL on failure.
The ddi_taskq_dispatch() function returns DDI_FAILURE if it can't dis‐
patch a task and returns DDI_SUCCESS if dispatch succeeded.
The ddi_taskq_suspended() function returns B_TRUE if taskq is sus‐
pended. Otherwise B_FALSE is returned.
CONTEXT
All functions may be called from the user or kernel contexts.
Addtionally, the ddi_taskq_dispatch function may be called from the
interrupt context only if the DDI_NOSLEEP flag is set.
SunOS 5.10 1 Mar 2005 taskq(9F)
