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2 pj 1
/*
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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: join.c,v 1.3 2003-01-07 17:07:49 pj Exp $
2 pj 22
 
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 File:        $File$
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 Revision:    $Revision: 1.3 $
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 Last update: $Date: 2003-01-07 17:07:49 $
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 ------------
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 task join and related primitives
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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 <stdarg.h>
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#include <ll/ll.h>
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#include <ll/stdlib.h>
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#include <ll/stdio.h>
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#include <ll/string.h>
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#include <kernel/config.h>
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#include <kernel/model.h>
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#include <kernel/const.h>
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#include <sys/types.h>
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#include <kernel/types.h>
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#include <kernel/descr.h>
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#include <errno.h>
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#include <kernel/var.h>
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#include <kernel/func.h>
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static int taskjoin_once = 1;
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/* this is the test that is done when a task is being killed
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   and it is waiting on a sigwait */
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static int taskjoin_cancellation_point(PID i, void *arg)
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{
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    LEVEL l;
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    if (proc_table[i].status == WAIT_JOIN) {
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      /* the task that have to be killed is waiting on a task_join.
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         we reset the data structures set in task_join and then when the
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         task will exit from task_join it will fall into a task_testcancel */
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      proc_table[ proc_table[i].shadow ].waiting_for_me = NIL;
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      proc_table[i].shadow = i;
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      l = proc_table[i].task_level;
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      level_table[l]->public_unblock(l,i);
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      return 1;
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    }
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    return 0;
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}
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/*+ this function suspends execution of the calling task until the target
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    task terminates, unless the target task has already terminated.
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    It works like the pthread_join +*/
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int task_join(PID p, void **value)
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{
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  PID x;           /* used to follow the shadow chain */
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  int blocked = 0; /* a flag */
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  LEVEL l;
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  /* task_join is a cancellation point... if the task is suspended
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     the control on the status is done in task_kill */
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  task_testcancel();
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  /* some controls on the task p */
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  if (p<0 || p>=MAX_PROC)                       return ESRCH;
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  if (proc_table[p].status == FREE &&
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      !(proc_table[p].control & WAIT_FOR_JOIN)) return ESRCH;
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  if (!(proc_table[p].control & TASK_JOINABLE)) return EINVAL;
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  proc_table[exec_shadow].context = kern_context_save();
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  /* first, if it is the first time that the task_join is called,
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     register the cancellation point */
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  if (taskjoin_once) {
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    taskjoin_once = 0;
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    register_cancellation_point(taskjoin_cancellation_point, NULL);
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  }
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  if (proc_table[p].waiting_for_me != NIL) {
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    kern_context_load(proc_table[exec_shadow].context);
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    return EINVAL;
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  }
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  /* deadlock checks; we check the shadow chain to prevent cycles */
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  x = p;
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  do {
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    x = proc_table[x].shadow;
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    if (x == exec_shadow) {
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      kern_context_load(proc_table[exec_shadow].context);
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      return EDEADLK;
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    }
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  } while (x != proc_table[x].shadow);
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  /* we prepare all the stuffs for joining the target task... */
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  if (!(proc_table[p].control & WAIT_FOR_JOIN)) {
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    /* the target task is already running... so we block yhe current task
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       on it!!!
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       Note: It is not correct to set only the shadow and reschedule, as done
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       with the mutexes, because there is no inheritance with join...
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       Normally we have to call task_extract because blocking on join is
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       like blocking on a classic semaphore.
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       Althought, we set the shadow because:
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       - if the task call task_join when holding a mutex (AAARRRGGHHH!!!)
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         the system continue working...
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       - The deadlock detection strategy works on shadows...
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       Setting shadows means also that implementation of mutexes that
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       manage shadows in a strange way WILL NOT WORK with task_join
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       (for example, the srp.c module doesn't work with task_join) */
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    proc_table[p].waiting_for_me = exec_shadow;
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    proc_table[exec_shadow].shadow = p;
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    kern_epilogue_macro();
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    /* now, we block the current task, waiting the end of the target task */
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    l = proc_table[exec_shadow].task_level;
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    level_table[l]->public_block(l,exec_shadow);
2 pj 159
    proc_table[exec_shadow].status = WAIT_JOIN;
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    exec = exec_shadow = -1;
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    scheduler();
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    /* note that we don't use kern_context_load because when rescheduled
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       we remain in kernel mode... */
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    ll_context_to(proc_table[exec_shadow].context);
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167
    blocked = 1;
168
  }
169
  /* task-join is a cancellation point; if the task is killed while it is
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     waiting on a join, the task-kill set the kill-request bit and wake up
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     the task, so it can die :-) */
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  task_testcancel();
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  /* the target task is terminated... we reset the WAIT_FOR_JOIN flag
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     so the descriptor can be reused by task_create; if the descriptor was
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     already discarded by the task_create, we reinsert it into the free
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     queue */
178
  proc_table[p].control &= ~WAIT_FOR_JOIN;
179
  if (proc_table[p].control & DESCRIPTOR_DISCARDED)
29 pj 180
    iq_insertfirst(p, &freedesc);
2 pj 181
 
182
  if (value)
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    *value = proc_table[p].return_value;
184
 
185
  if (blocked) {
186
    /* the ll_context_to is already done... */
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    kern_deliver_pending_signals();
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    sti();
189
  }
190
  else
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    /* we did a kern_context_save before... */
192
    kern_context_load(proc_table[exec_shadow].context);
193
 
194
  return 0;
195
}
196
 
197
/*+ this function set the detach state of a task to joinable. This function
198
    is not present in Posix standard...
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    returns ESRCH if p is non correct +*/
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int task_joinable(PID p)
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{
202
  if (p<0 || p>=MAX_PROC)                       return ESRCH;
203
  if (proc_table[p].status == FREE)             return ESRCH;
204
 
205
  kern_cli();
206
  proc_table[p].control |= TASK_JOINABLE;
207
  kern_sti();
208
  return 0;
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}
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/*+ this function set the detach state of a task to detached. This function
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    works as the posix's pthread_detach
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    returns EINVAL if p can't be joined (or currently a task has done a
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    join on it (condition not provided in posix)
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    ESRCH if p is not correct +*/
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int task_unjoinable(PID p)
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{
218
  if (p<0 || p>=MAX_PROC)                       return ESRCH;
219
  if (proc_table[p].status == FREE)             return ESRCH;
220
 
221
  kern_cli();
222
 
223
  if (!(proc_table[p].control & TASK_JOINABLE) ||
224
      proc_table[p].waiting_for_me != NIL) {
225
    kern_sti();
226
    return EINVAL;
227
  }
228
 
229
  proc_table[p].control |= TASK_JOINABLE;
230
 
231
  kern_sti();
232
  return 0;
233
}