1.\" -*- nroff -*- 2.\" 3.\" Copyright (c) 2000 Doug Rabson 4.\" 5.\" All rights reserved. 6.\" 7.\" This program is free software. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR 19.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 20.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 21.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT, 22.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 23.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 24.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 25.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 26.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 27.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 28.\" 29.\" $FreeBSD$ 30.\" 31.Dd May 12, 2000 32.Dt TASKQUEUE 9 33.Os 34.Sh NAME 35.Nm taskqueue 36.Nd asynchronous task execution 37.Sh SYNOPSIS 38.In sys/param.h 39.In sys/kernel.h 40.In sys/malloc.h 41.In sys/queue.h 42.In sys/taskqueue.h 43.Bd -literal 44 45typedef void (*task_fn)(void *context, int pending); 46 47typedef void (*taskqueue_enqueue_fn)(void *context); 48 49struct task { 50 STAILQ_ENTRY(task) ta_link; /* link for queue */ 51 int ta_pending; /* count times queued */ 52 int ta_priority; /* priority of task in queue */ 53 task_fn ta_func; /* task handler */ 54 void *ta_context; /* argument for handler */ 55}; 56 57.Ed 58.Ft struct taskqueue * 59.Fn taskqueue_create "const char *name" "int mflags" "taskqueue_enqueue_fn enqueue" "void *context" 60.Ft void 61.Fn taskqueue_free "struct taskqueue *queue" 62.Ft struct taskqueue * 63.Fn taskqueue_find "const char *name" 64.Ft int 65.Fn taskqueue_enqueue "struct taskqueue *queue" "struct task *task" 66.Ft void 67.Fn taskqueue_run "struct taskqueue *queue" 68.Fn TASK_INIT "struct task *task" "int priority" "task_fn_t *func" "void *context" 69.Fn TASKQUEUE_DECLARE "name" 70.Fn TASKQUEUE_DEFINE "name" "taskqueue_enqueue_fn enqueue" "void *context" "init" 71.Sh DESCRIPTION 72These functions provide a simple interface for asynchronous execution 73of code. 74.Pp 75The function 76.Fn taskqueue_create 77is used to create new queues. 78The arguments to 79.Fn taskqueue_create 80include a name which should be unique, 81a set of 82.Xr malloc 9 83flags which specify whether the call to 84.Fn malloc 85is allowed to sleep 86and a function which is called from 87.Fn taskqueue_enqueue 88when a task is added to the queue 89.\" XXX The rest of the sentence gets lots in relation to the first part. 90to allow the queue to arrange to be run later 91(for instance by scheduling a software interrupt or waking a kernel 92thread). 93.Pp 94The function 95.Fn taskqueue_free 96should be used to remove the queue from the global list of queues 97and free the memory used by the queue. 98Any tasks which are on the queue will be executed at this time. 99.Pp 100The system maintains a list of all queues which can be searched using 101.Fn taskqueue_find . 102The first queue whose name matches is returned, otherwise 103.Dv NULL . 104.Pp 105To add a task to the list of tasks queued on a taskqueue, call 106.Fn taskqueue_enqueue 107with pointers to the queue and task. 108If the task's 109.Va ta_pending 110field is non-zero, 111then it is simply incremented to reflect the number of times the task 112was enqueued. 113Otherwise, 114the task is added to the list before the first task which has a lower 115.Va ta_priority 116value or at the end of the list if no tasks have a lower priority. 117Enqueueing a task does not perform any memory allocation which makes 118it suitable for calling from an interrupt handler. 119This function will return 120.Er EPIPE 121if the queue is being freed. 122.Pp 123To execute all the tasks on a queue, 124call 125.Fn taskqueue_run . 126When a task is executed, 127first it is removed from the queue, 128the value of 129.Va ta_pending 130is recorded and then the field is zeroed. 131The function 132.Va ta_func 133from the task structure is called with the value of the field 134.Va ta_context 135as its first argument 136and the value of 137.Va ta_pending 138as its second argument. 139.Pp 140A convenience macro, 141.Fn TASK_INIT "task" "priority" "func" "context" 142is provided to initialise a 143.Va task 144structure. 145The values of 146.Va priority , 147.Va func , 148and 149.Va context 150are simply copied into the task structure fields and the 151.Va ta_pending 152field is cleared. 153.Pp 154Two macros 155.Fn TASKQUEUE_DECLARE "name" 156and 157.Fn TASKQUEUE_DEFINE "name" "enqueue" "context" "init" 158are used to declare a reference to a global queue 159and to define the implementation of the queue. 160The 161.Fn TASKQUEUE_DEFINE 162macro arranges to call 163.Fn taskqueue_create 164with the values of its 165.Va name , 166.Va enqueue 167and 168.Va context 169arguments during system initialisation. 170After calling 171.Fn taskqueue_create , 172the 173.Va init 174argument to the macro is executed as a C statement, 175allowing any further initialisation to be performed 176(such as registering an interrupt handler etc.) 177.Pp 178The system provides a global taskqueue, 179.Va taskqueue_swi , 180which is run via a software interrupt mechanism. 181To use this queue, 182call 183.Fn taskqueue_enqueue 184with the value of the global variable 185.Va taskqueue_swi . 186The queue will be run at 187.\" XXX This should be a cross-reference (Xr), but there is no MANLINKS 188.\" entry for splsofttq.9 yet. 189.Fn splsofttq . 190.Pp 191This queue can be used, 192for instance, for implementing interrupt handlers which must perform a 193significant amount of processing in the handler. 194The hardware interrupt handler would perform minimal processing of the 195interrupt and then enqueue a task to finish the work. 196This reduces to a minimum 197the amount of time spent with interrupts disabled. 198.Sh HISTORY 199This interface first appeared in 200.Fx 5.0 . 201There is a similar facility called tqueue in the Linux kernel. 202.Sh AUTHORS 203This man page was written by 204.An Doug Rabson . 205