Date: Tue, 16 May 2000 21:48:21 +0100 (BST) From: Doug Rabson <dfr@nlsystems.com> To: arch@freebsd.org Subject: A new api for asynchronous task execution (2) Message-ID: <Pine.BSF.4.21.0005162147060.47945-300000@salmon.nlsystems.com>
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[-- Attachment #1 --]
Ok, after the last set of feedback, I have updated the design
somewhat. This is the latest manpage and I have attached a sample
implementation (not thoroughly tested).
TASKQUEUE(9) FreeBSD Kernel Developer's Manual TASKQUEUE(9)
NAME
taskqueue - asynchronous task execution
SYNOPSIS
#include <sys/param.h>
#include <sys/queue.h>
#include <sys/taskqueue.h>
typedef void (*task_fn)(void *context, int pending);
typedef void (*taskqueue_enqueue_fn)(void *context);
struct task {
STAILQ_ENTRY(task) link; /* link for queue */
int pending; /* count times task is queued */
task_fn func; /* task handler */
void *context; /* argument for handler */
};
#define TQ_DEF 0 /* use blocking mutex */
#define TQ_SPIN 1 /* use spin mutex */
void
taskqueue_init(struct taskqueue *queue, const char *name, int flags,
taskqueue_enqueue_fn enqueue, void *context)
struct taskqueue *
taskqueue_find(const char *name)
void
taskqueue_enqueue(struct taskqueue *queue, struct task *task)
void
taskqueue_run(struct taskqueue *queue)
DESCRIPTION
These functions provide a simple interface for asynchronous execution of
code.
Before a queue can be used, it must first be initialised with
taskqueue_init(). The arguments to taskqueue_init() include a name which
should be unique, a flag which specifies the type of SMP mutex used to
protect the queue and a function which is called from taskqueue_enqueue()
when a task is added to the queue to allow the queue to arrange to be run
later (for instance by scheduling a software interrupt or waking a kernel
thread).
The function taskqueue_free() should be used to remove the queue from the
global list of queues. Any tasks which are on the queue will be executed
at this time.
The system maintains a list of all queues which can be searched using
taskqueue_find(). The first queue whose name matches is returned, other-
wise NULL.
To add a task to the list of tasks queued on a taskqueue, call
taskqueue_enqueue() with pointers to the queue and task. If the task's
pending field is zero, the task is added to the end of the list and
pending is set to one, otherwise, pending is incremented. Enqueueing a
task does not perform any memory allocation which makes it suitable for
calling from an interrupt handler.
To execute all the tasks on a queue, call taskqueue_run(). When a task
is executed, first it is removed from the queue, the value of pending is
recorded and the field is zeroed. The function func from the task struc-
ture is called with the value of the field context its first argument and
the value of pending as its second argument.
The system provides a global taskqueue, taskqueue_swi, which is run via a
software interrupt mechanism. To use this queue, call
taskqueue_enqueue() with the value of the global variable taskqueue_swi.
The queue will be run at splsofttq().
This queue can be used, for instance, for implementing interrupt handlers
which must perform a significant amount of processing in the handler.
The hardware interrupt handler would perform minimal processing of the
interrupt and then enqueue a task to finish the work. This reduces the
amount of time spent with interrupts disabled to a minimum.
HISTORY
This interface first appeared in FreeBSD 5.0. There is a similar facili-
ty called tqueue in the Linux kernel.
AUTHORS
This man page was written by Doug Rabson.
FreeBSD May 12, 2000 2
--
Doug Rabson Mail: dfr@nlsystems.com
Nonlinear Systems Ltd. Phone: +44 20 8442 9037
[-- Attachment #2 --]
/*-
* Copyright (c) 2000 Doug Rabson
* 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.
*
* $FreeBSD$
*/
#include <sys/param.h>
#include <sys/queue.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/taskqueue.h>
#include <sys/interrupt.h>
#include <sys/malloc.h>
#include <machine/ipl.h>
MALLOC_DEFINE(M_TASKQUEUE, "taskqueue", "Task Queues");
static STAILQ_HEAD(taskqueue_list, taskqueue) taskqueue_queues;
struct taskqueue {
STAILQ_ENTRY(taskqueue) link;
STAILQ_HEAD(, task) queue;
const char *name;
taskqueue_enqueue_fn enqueue;
void *context;
};
struct taskqueue *
taskqueue_create(const char *name, int flags,
taskqueue_enqueue_fn enqueue, void *context)
{
struct taskqueue *queue;
queue = malloc(sizeof(struct taskqueue), M_TASKQUEUE, M_NOWAIT);
if (!queue)
return 0;
STAILQ_INSERT_TAIL(&taskqueue_queues, queue, link);
STAILQ_INIT(&queue->queue);
queue->name = name;
queue->enqueue = enqueue;
queue->context = context;
return queue;
}
void
taskqueue_free(struct taskqueue *queue)
{
int s = splhigh();
taskqueue_run(queue);
STAILQ_REMOVE(&taskqueue_queues, queue, taskqueue, link);
splx(s);
free(queue, M_TASKQUEUE);
}
struct taskqueue *
taskqueue_find(const char *name)
{
struct taskqueue *queue;
STAILQ_FOREACH(queue, &taskqueue_queues, link)
if (!strcmp(queue->name, name))
return queue;
return 0;
}
void
taskqueue_enqueue(struct taskqueue *queue, struct task *task)
{
int s = splhigh();
/*
* Count multiple enqueues.
*/
if (task->pending) {
task->pending++;
splx(s);
return;
}
STAILQ_INSERT_TAIL(&queue->queue, task, link);
task->pending = 1;
if (queue->enqueue)
queue->enqueue(queue->context);
splx(s);
}
void
taskqueue_run(struct taskqueue *queue)
{
int s;
struct task *task;
int pending;
s = splhigh();
while (STAILQ_FIRST(&queue->queue)) {
/*
* Carefully remove the first task from the queue and
* zero its pending count.
*/
task = STAILQ_FIRST(&queue->queue);
STAILQ_REMOVE_HEAD(&queue->queue, link);
pending = task->pending;
task->pending = 0;
splx(s);
task->func(task->context, pending);
s = splhigh();
}
splx(s);
}
static void
taskqueue_swi_enqueue(void *context)
{
setsofttq();
}
static void
taskqueue_swi_run(void)
{
taskqueue_run(taskqueue_swi);
}
TASKQUEUE_DEFINE(swi, TQ_DEF, taskqueue_swi_enqueue, 0,
register_swi(SWI_TQ, taskqueue_swi_run));
[-- Attachment #3 --]
/*-
* Copyright (c) 2000 Doug Rabson
* 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.
*
* $FreeBSD$
*/
#ifndef _SYS_TASKQUEUE_H_
#define _SYS_TASKQUEUE_H_
#ifdef _KERNEL
struct taskqueue;
/*
* Each task includes a function which is called from
* taskqueue_run(). The first argument is taken from the 'context'
* field of struct task and the second argument is a count of how many
* times the task was enqueued before the call to taskqueue_run().
*/
typedef void (*task_fn)(void *context, int pending);
/*
* A notification callback function which is called from
* taskqueue_enqueue(). The context argument is given in the call to
* taskqueue_init(). This function would normally be used to allow the
* queue to arrange to run itself later (e.g. by scheduling a software
* interrupt or waking a kernel thread).
*/
typedef void (*taskqueue_enqueue_fn)(void *context);
struct task {
STAILQ_ENTRY(task) link; /* link for queue */
int pending; /* count times task is queued */
task_fn func; /* task handler */
void *context; /* argument for handler */
};
/*
* Flags for taskqueue_init() which will control the properties of a
* mutex will be used to protect the queue.
*
* Note: this is not currently used but will be used in a future
* implementation of SMP.
*/
#define TQ_DEF 0 /* use blocking mutex */
#define TQ_SPIN 1 /* use spin mutex */
struct taskqueue *taskqueue_create(const char *name, int flags,
taskqueue_enqueue_fn enqueue,
void *context);
void taskqueue_free(struct taskqueue *queue);
struct taskqueue *taskqueue_find(const char *name);
void taskqueue_enqueue(struct taskqueue *queue,
struct task *task);
void taskqueue_run(struct taskqueue *queue);
/*
* Declare a reference to a taskqueue.
*/
#define TASKQUEUE_DECLARE(name) \
\
extern struct taskqueue *taskqueue_##name
/*
* Define and initialise a taskqueue.
*/
#define TASKQUEUE_DEFINE(name, flags, enqueue, context, init) \
\
struct taskqueue *taskqueue_##name; \
\
static void \
taskqueue_define_##name(void *arg) \
{ \
taskqueue_##name = \
taskqueue_create(#name, flags, enqueue, context); \
init; \
} \
\
SYSINIT(taskqueue_##name, SI_SUB_CONFIGURE, SI_ORDER_SECOND, \
taskqueue_define_##name, NULL);
/*
* This queue is serviced by a software interrupt handler. To enqueue
* a task, call taskqueue_enqueue(&taskqueue_swi, &task).
*/
TASKQUEUE_DECLARE(swi);
#endif /* _KERNEL */
#endif /* !_SYS_TASKQUEUE_H_ */
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