.\"	$NetBSD: workqueue.9,v 1.15 2020/09/08 17:02:18 riastradh Exp $
.\"
.\" Copyright (c)2005 YAMAMOTO Takashi,
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" ------------------------------------------------------------
.Dd December 28, 2017
.Dt WORKQUEUE 9
.Os
.\" ------------------------------------------------------------
.Sh NAME
.Nm workqueue
.Nd simple do-it-in-thread-context framework
.\" ------------------------------------------------------------
.Sh SYNOPSIS
.In sys/workqueue.h
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft int
.Fn workqueue_create \
"struct workqueue **wqp" "const char *name" \
"void (*func)(struct work *, void *)" "void *arg" \
"pri_t prio" "int ipl" "int flags"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft void
.Fn workqueue_enqueue \
"struct workqueue *wq" "struct work *wk" "struct cpu_info *ci"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft void
.Fn workqueue_wait \
"struct workqueue *wq" "struct work *wk"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft void
.Fn workqueue_destroy \
"struct workqueue *wq"
.\" ------------------------------------------------------------
.Sh DESCRIPTION
The
.Nm
utility routines are provided to defer work which is needed to be
processed in a thread context.
.Pp
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Fn workqueue_create
creates a workqueue.
It takes the following arguments:
.Bl -tag -width flags
.It Fa wqp
Specify where to store the created workqueue.
.It Fa name
The name of the workqueue.
.It Fa func
The function to be called for each
.Fa work .
.It Fa arg
An argument to be passed as a second argument of
.Fa func .
.It Fa prio
The priority level for the worker threads.
.It Fa ipl
The highest IPL at which this workqueue is used.
.It Fa flags
The value of 0 indicates a standard create operation, however the following
flags may be bitwise ORed together:
.Bl -tag -width WQ_MPSAFE
.It Dv WQ_FPU
Specifies that the kthread must be allowed to use any machine-dependent
per-CPU floating-point units or SIMD vector units, as in
.Xr kthread_fpu_enter 9 / Xr kthread_fpu_exit 9 ,
when it executes the worker function.
.It Dv WQ_MPSAFE
Specifies that the workqueue is multiprocessor safe and does its own locking;
otherwise the kernel lock will be held while processing work.
.It Dv WQ_PERCPU
Specifies that the workqueue should have a separate queue for each CPU,
thus the work could be enqueued on concrete CPUs.
.El
.El
.Pp
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Fn workqueue_enqueue
enqueues the work
.Fa wk
into the workqueue
.Fa wq .
.Pp
If the
.Dv WQ_PERCPU
flag was set on workqueue creation, the
.Fa ci
argument may be used to specify the CPU on which the work should
be enqueued.
Also it may be
.Dv NULL ,
then work will be enqueued on the current CPU.
If
.Dv WQ_PERCPU
flag was not set,
.Fa ci
must be
.Dv NULL .
.Pp
The enqueued work will be processed in a thread context.
A work must not be enqueued again until the callback is called by
the
.Nm
framework.
.Pp
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Fn workqueue_wait
waits for a specified work
.Fa wk
on the workqueue
.Fa wq
to finish.
The caller must ensure that
.Fa wk
will not be enqueued to the workqueue again until after
.Fn workqueue_wait
returns.
.Pp
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Fn workqueue_destroy
destroys a workqueue and frees associated resources.
The caller should ensure that the workqueue has no work enqueued beforehand.
.\" ------------------------------------------------------------
.Sh RETURN VALUES
.Fn workqueue_create
returns 0 on success.
Otherwise, it returns an
.Xr errno 2 .
.\" ------------------------------------------------------------
.Sh CODE REFERENCES
The
.Nm
subsystem is implemented within the file
.Pa sys/kern/subr_workqueue.c .
.\" ------------------------------------------------------------
.Sh SEE ALSO
.Xr callout 9 ,
.Xr condvar 9 ,
.Xr kthread 9 ,
.Xr softint 9