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/*
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 * Project: S.Ha.R.K.
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 *
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 * Coordinators:
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 *   Giorgio Buttazzo    <giorgio@sssup.it>
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 *   Paolo Gai           <pj@gandalf.sssup.it>
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 *
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 * Authors     :
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 *   Paolo Gai           <pj@gandalf.sssup.it>
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 *   (see the web pages for full authors list)
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 *
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 * ReTiS Lab (Scuola Superiore S.Anna - Pisa - Italy)
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 *
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 * http://www.sssup.it
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 * http://retis.sssup.it
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 * http://shark.sssup.it
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 */
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/**
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 ------------
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 CVS :        $Id: int_sem.c,v 1.4 2003-11-05 15:05:11 giacomo Exp $
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 File:        $File$
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 Revision:    $Revision: 1.4 $
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 Last update: $Date: 2003-11-05 15:05:11 $
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 ------------
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 Internal semaphores.
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 They are different from the Posix semaphores and the mutexes because:
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 - internal_sem_wait is not a cancellation point
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 - there are no limits on the semaphores that can be created
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   (they works like a mutex_t...)
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 - the queuing policy is FIFO
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 - Be Careful!
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   they are made to be fast... so not so many controls are done!!!
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**/
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/*
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 * Copyright (C) 2000 Paolo Gai
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 *
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 * This program is free software; you can redistribute it and/or modify
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 * it under the terms of the GNU General Public License as published by
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 * the Free Software Foundation; either version 2 of the License, or
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 * (at your option) any later version.
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 *
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 * This program is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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 * GNU General Public License for more details.
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 *
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 * You should have received a copy of the GNU General Public License
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 * along with this program; if not, write to the Free Software
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 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
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 *
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 */
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#include <kernel/int_sem.h>
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#include <kernel/var.h>
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#include <kernel/func.h>
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/* Wait status for this library */
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#define INTERNAL_SEM_WAIT LIB_STATUS_BASE
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void internal_sem_init(internal_sem_t *s, int value)
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{
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  s->count = value;
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  iq_init(&s->blocked,&freedesc,0);
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}
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void internal_sem_wait(internal_sem_t *s)
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{
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  SYS_FLAGS f;
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  f = kern_fsave();
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  if (s->count) {
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    s->count--;
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    kern_frestore(f);
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    return;
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  }
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  else {                /* We must block exec task   */
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    LEVEL l;            /* for readableness only */
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    proc_table[exec_shadow].context = kern_context_save();
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    kern_epilogue_macro();
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    l = proc_table[exec_shadow].task_level;
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    level_table[l]->public_block(l,exec_shadow);
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    /* we insert the task in the semaphore queue */
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    proc_table[exec_shadow].status = INTERNAL_SEM_WAIT;
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    iq_insertlast(exec_shadow,&s->blocked);
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    /* and finally we reschedule */
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    exec = exec_shadow = -1;
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    scheduler();
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    ll_context_to(proc_table[exec_shadow].context);
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    kern_after_dispatch();
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    kern_frestore(f);
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  }
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}
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/* return 0 if the counter is decremented, -1 if not */
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int internal_sem_trywait(internal_sem_t *s)
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{
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  SYS_FLAGS f;
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  f = kern_fsave();
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  if (s->count) {
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    s->count--;
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    kern_frestore(f);
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    return 0;
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  }
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  return -1;
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}
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void internal_sem_post(internal_sem_t *s)
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{
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  proc_table[exec_shadow].context = kern_context_save();
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  if (s->blocked.first != -1) {
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    register PID p;
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    register LEVEL l;
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    p = iq_getfirst(&s->blocked);
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    l = proc_table[p].task_level;
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    level_table[l]->public_unblock(l,p);
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    scheduler();
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  }
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  else
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    s->count++;
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  kern_context_load(proc_table[exec_shadow].context);
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}
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int internal_sem_getvalue(internal_sem_t *s)
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{
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  register int returnvalue;
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  SYS_FLAGS f;
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  f = kern_fsave();
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  if (s->blocked.first == -1)
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    returnvalue = s->count;
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  else
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    returnvalue = -1;
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  kern_frestore(f);
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  return returnvalue;
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}