source: rtems-libbsd/rtemsbsd/src/rtems-bsd-taskqueue.c @ 0ff1733

/**
 * @file
 *
 * @ingroup rtems_bsd_rtems
 *
 * @brief TODO.
 */

/*
 *  COPYRIGHT (c) 1989-2012.
 *  On-Line Applications Research Corporation (OAR).
 *
 * The license and distribution terms for this file may be
 * found in the file LICENSE in this distribution or at
 * http://www.rtems.com/license/LICENSE.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include <rtems.h>
#include <rtems/error.h>
#include <freebsd/machine/rtems-bsd-taskqueue.h>

/*
#define STATIC static
*/
#undef  DEBUG

#ifdef DEBUG
#include <stdio.h>
#ifndef STATIC
#define STATIC
#endif
#else
#ifndef STATIC
#define STATIC static
#endif
#endif

#define TQ_WAKE_EVENT RTEMS_EVENT_0

/* This implementation is extremely simple; we assume
 * that all taskqueues (and as a matter of fact there is
 * only a single one) are manipulated with the rtems
 * bsdnet semaphore held. I.e.,
 *   taskqueue_enqueue()
 *   taskqueue_drain()
 *   etc.
 * are called from an environment that holds the
 * bsdnet semaphore.
 * Likewise, the thread that works the taskqueue
 * holds the semaphore while doing so.
 *
 */

/* use single-linked list; 'drain' which would benefit from
 * double-linked list is seldom used and performance doesn't
 * matter much there. OTOH, the frequent case of working
 * the list + enqueueing is more efficient for the single-linked
 * list.
struct task {
        struct task *ta_next;
        int                  ta_pending;
        int                  ta_priority;
        task_fn      ta_fn;
        void        *ta_fn_arg;
};
 */

struct taskqueue {
        struct task anchor;
        struct task *tail;
        tq_enq_fn   enq_fn;
        void       *enq_fn_arg;
        rtems_id    tid;
};


STATIC struct taskqueue the_taskqueue = {
        { 0, 0, 0, 0, 0 },
        &the_taskqueue.anchor,
        taskqueue_thread_enqueue,
        &taskqueue_fast,
        0
};

struct taskqueue *taskqueue_fast = &the_taskqueue;
struct taskqueue *taskqueue_swi = NULL;

struct taskqueue *
taskqueue_create(const char *name, int mflags, tq_enq_fn enq_fn, void *arg)
{
        if ( enq_fn != taskqueue_thread_enqueue )
                rtems_panic("rtems_taskqueue: attempt to create non-standard TQ; implementation needs to be modified\n");
        return &the_taskqueue;
}

struct taskqueue *
taskqueue_create_fast(const char *name, int mflags, tq_enq_fn enq_fn, void *arg)
{
        return taskqueue_create(name, mflags, enq_fn, arg);
}

/* taskqueue_enqueue must be allowed from an ISR;
 * hence, all critical list manipulation must lock out
 * interrupts...
 */
int
taskqueue_enqueue(struct taskqueue *tq, struct task *ta)
{
rtems_interrupt_level l;

rtems_interrupt_disable(l);
        if ( 0 == ta->ta_pending ++ ) {
                /* hook into list */
                ta->ta_next       = 0;
                tq->tail->ta_next = ta;
                tq->tail          = ta;
        }
        tq->enq_fn(tq->enq_fn_arg);
rtems_interrupt_enable(l);
        return 0;
}

void
taskqueue_thread_enqueue(void *ctxt)
{
int                   dopost;
/* pointer-to-pointer is what bsd provides; we currently
 * follow the scheme even we don't directly use the argument
 * passed to taskqueue_create...
 */
struct taskqueue *tq = *(struct taskqueue **)ctxt;
        /* If this is the first entry on the list then the
         * task needs to be notified...
         */
        dopost = ( tq->anchor.ta_next == tq->tail && 1 == tq->tail->ta_pending );

        if ( dopost )
                rtems_event_send(tq->tid, TQ_WAKE_EVENT);
}

/* Returns 0 on success */
int
taskqueue_start_threads(struct taskqueue **ptq, int count, int prio, const char *fmt, ...)
{
        if ( count != 1 )
                rtems_panic("rtems_taskqueue: taskqueue_start_threads cannot currently deal with count != 1\n");
        
        /* Do (non thread-safe) lazy init as a fallback */
        if ( ! the_taskqueue.tid )
                rtems_taskqueue_initialize();
        return 0;
}

void
taskqueue_drain(struct taskqueue *tq, struct task *ta)
{
rtems_interrupt_level l;
struct task *p, *q;
int    i;

        /* find predecessor; searching the list should be
         * safe; an ISR might append a new record to the tail
         * while we are working but that should be OK.
         */
        for ( p = &tq->anchor; (q = p->ta_next); p=q ) {
                if ( q == ta ) {
                rtems_interrupt_disable(l);
                        /* found; do work */
                        /* remember 'pending' count and extract */
                        i              = ta->ta_pending;
                        ta->ta_pending = 0;
                        p->ta_next     = ta->ta_next;
                        ta->ta_next    = 0;
                        /* adjust tail */
                        if ( tq->tail == q )
                                tq->tail = p;
                rtems_interrupt_enable(l);
                        for ( ; i>0; i-- ) {
                                ta->ta_fn(ta->ta_fn_arg, i);
                        }
                        return;
                }
        }
}

/* work the task queue and return
 * nonzero if the list is not empty
 * (which means that some callback has
 * rescheduled itself)
 */
static void *
taskqueue_work(struct taskqueue *tq)
{
rtems_interrupt_level l;
struct task   *p, *q;
task_fn        f;
void        *arg;
int            i;

/* work off a temporary list in case any callback reschedules
 * itself or if new tasks are queued from an ISR.
 */
rtems_interrupt_disable(l);
        p = tq->anchor.ta_next;

        tq->anchor.ta_next = 0;
        tq->tail           = &tq->anchor;
rtems_interrupt_enable(l);

        while ( (q=p) ) {
        rtems_interrupt_disable(l);
                i = q->ta_pending;
                q->ta_pending = 0;
                /* extract */
                p          = q->ta_next;
                q->ta_next = 0;
                f          = q->ta_fn;
                arg        = q->ta_fn_arg;
        rtems_interrupt_enable(l);
                for ( ; i>0; i-- ) {
                        f(arg, i);
                }
        }
        return tq->anchor.ta_next;
}

void
taskqueue_free(struct taskqueue *tq)
{
        taskqueue_work(tq);
}

static void
taskqueueDoWork(void *arg)
{
struct taskqueue *tq = arg;
rtems_event_set  evs;
rtems_status_code sc;
        while ( 1 ) {
                sc = rtems_event_receive(TQ_WAKE_EVENT, RTEMS_EVENT_ANY | RTEMS_WAIT, RTEMS_NO_TIMEOUT, &evs);
                if ( RTEMS_SUCCESSFUL != sc ) {
                        rtems_error(sc,"rtems_taskqueue: taskqueueDoWork() unable to receive wakup event\n");
                        rtems_panic("Can't proceed\n");
                }
                if ( taskqueue_work(tq) ) {
#if 0
                        /* chance to reschedule */
                        rtems_bsdnet_semaphore_release();
                        rtems_task_wake_after(0);
                        rtems_bsdnet_semaphore_obtain();
#else
                        /* hopefully, releasing the semaphore (as part of bsdnet_event_receive)
                         * and obtaining the event (which has been posted already)
                         * yields the CPU if necessary...
                         */
#endif
                }
        }
}

#ifdef DEBUG
struct task_dbg {
        struct task t;
        char        *nm;
};

struct task_dbg taskA = {
        {0},
        "taskA"
};

struct task_dbg taskB = {
        {0},
        "taskB"
};

struct task_dbg taskC = {
        {0},
        "taskC"
};

static void the_task_fn(void *arg, int pending)
{
struct task_dbg *td = arg;
        printf("%s (pending: %i)\n", td->nm, pending);
        /* Test rescheduling */
        if ( pending > 3 )
                taskqueue_enqueue(&the_taskqueue,&td->t);
}

void taskqueue_dump()
{
struct task *p;
        printf("Anchor %p, Tail %p\n", &the_taskqueue.anchor, the_taskqueue.tail);
        for ( p = the_taskqueue.anchor.ta_next; p; p=p->ta_next ) {
                printf("%p: (pending %2i, next %p)\n",
                        p, p->ta_pending, p->ta_next);
        }
}
#endif

rtems_id
rtems_taskqueue_initialize()
{
#ifdef DEBUG
        TASK_INIT( &taskA.t, 0, the_task_fn, &taskA );
        TASK_INIT( &taskB.t, 0, the_task_fn, &taskB );
        TASK_INIT( &taskC.t, 0, the_task_fn, &taskC );
#endif
        if ( ! the_taskqueue.tid )
                the_taskqueue.tid = rtems_bsdnet_newproc("tskq", 10000, taskqueueDoWork, &the_taskqueue);
        return the_taskqueue.tid;
}

#ifdef DEBUG
void
_cexpModuleInitialize(void *u)
{
        rtems_bsdnet_initialize_network();
        the_taskqueue.tid = rtems_taskqueue_initialize();
}
#endif