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/* Copyright (C) 2004 David Decotigny
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
USA.
*/
#include <sos/errno.h>
#include <sos/klibc.h>
#include <sos/assert.h>
#include <sos/list.h>
#include "sched.h"
/**
* The definition of the scheduler queue. We could have used a normal
* kwaitq here, it would have had the same properties. But, in the
* definitive version (O(1) scheduler), the structure has to be a bit
* more complicated. So, in order to keep the changes as small as
* possible between this version and the definitive one, we don't use
* kwaitq here.
*/
static struct
{
unsigned int nr_threads;
struct sos_thread *thread_list;
} ready_queue;
sos_ret_t sos_sched_subsystem_setup()
{
memset(& ready_queue, 0x0, sizeof(ready_queue));
return SOS_OK;
}
/**
* Helper function to add a thread in a ready queue AND to change the
* state of the given thread to "READY".
*
* @param insert_at_tail TRUE to tell to add the thread at the end of
* the ready list. Otherwise it is added at the head of it.
*/
static sos_ret_t add_in_ready_queue(struct sos_thread *thr,
sos_bool_t insert_at_tail)
{
SOS_ASSERT_FATAL( (SOS_THR_CREATED == thr->state)
|| (SOS_THR_RUNNING == thr->state) /* Yield */
|| (SOS_THR_BLOCKED == thr->state) );
/* Add the thread to the CPU queue */
if (insert_at_tail)
list_add_tail_named(ready_queue.thread_list, thr,
ready.rdy_prev, ready.rdy_next);
else
list_add_head_named(ready_queue.thread_list, thr,
ready.rdy_prev, ready.rdy_next);
ready_queue.nr_threads ++;
/* Ok, thread is now really ready to be (re)started */
thr->state = SOS_THR_READY;
return SOS_OK;
}
sos_ret_t sos_sched_set_ready(struct sos_thread *thr)
{
sos_ret_t retval;
/* Don't do anything for already ready threads */
if (SOS_THR_READY == thr->state)
return SOS_OK;
/* Real-time thread: schedule it for the present turn */
retval = add_in_ready_queue(thr, TRUE);
return retval;
}
struct sos_thread * sos_reschedule(struct sos_thread *current_thread,
sos_bool_t do_yield)
{
if (SOS_THR_ZOMBIE == current_thread->state)
{
/* Don't think of returning to this thread since it is
terminated */
/* Nop */
}
else if (SOS_THR_BLOCKED != current_thread->state)
{
/* Take into account the current executing thread unless it is
marked blocked */
if (do_yield)
/* Ok, reserve it for next turn */
add_in_ready_queue(current_thread, TRUE);
else
/* Put it at the head of the active list */
add_in_ready_queue(current_thread, FALSE);
}
/* The next thread is that at the head of the ready list */
if (ready_queue.nr_threads > 0)
{
struct sos_thread *next_thr;
/* Queue is not empty: take the thread at its head */
next_thr = list_pop_head_named(ready_queue.thread_list,
ready.rdy_prev, ready.rdy_next);
ready_queue.nr_threads --;
return next_thr;
}
SOS_FATAL_ERROR("No kernel thread ready ?!");
return NULL;
}
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