Subversion Repositories shark

/*

 * Project: S.Ha.R.K.

 *

 * Coordinators:

 *   Giorgio Buttazzo    <giorgio@sssup.it>

 *   Paolo Gai           <pj@gandalf.sssup.it>

 *

 * Authors     :

 *   Paolo Gai           <pj@gandalf.sssup.it>

 *   (see the web pages for full authors list)

 *

 * ReTiS Lab (Scuola Superiore S.Anna - Pisa - Italy)

 *

 * http://www.sssup.it

 * http://retis.sssup.it

 * http://shark.sssup.it

 */

/**

 ------------

 CVS :        $Id: join.c,v 1.4 2003-11-05 15:05:11 giacomo Exp $

 File:        $File$

 Revision:    $Revision: 1.4 $

 Last update: $Date: 2003-11-05 15:05:11 $

 ------------

 task join and related primitives

**/

/*

 * Copyright (C) 2000 Paolo Gai

 *

 * 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 <stdarg.h>

#include <ll/ll.h>

#include <ll/stdlib.h>

#include <ll/stdio.h>

#include <ll/string.h>

#include <kernel/config.h>

#include <kernel/model.h>

#include <kernel/const.h>

#include <sys/types.h>

#include <kernel/types.h>

#include <kernel/descr.h>

#include <errno.h>

#include <kernel/var.h>

#include <kernel/func.h>

static int taskjoin_once = 1;

/* this is the test that is done when a task is being killed

   and it is waiting on a sigwait */

static int taskjoin_cancellation_point(PID i, void *arg)

{

    LEVEL l;

    if (proc_table[i].status == WAIT_JOIN) {

      /* the task that have to be killed is waiting on a task_join.

         we reset the data structures set in task_join and then when the

         task will exit from task_join it will fall into a task_testcancel */

      proc_table[ proc_table[i].shadow ].waiting_for_me = NIL;

      proc_table[i].shadow = i;

      l = proc_table[i].task_level;

      level_table[l]->public_unblock(l,i);

      return 1;

    }

    return 0;

}

/*+ this function suspends execution of the calling task until the target

    task terminates, unless the target task has already terminated.

    It works like the pthread_join +*/

int task_join(PID p, void **value)

{

  PID x;           /* used to follow the shadow chain */

  int blocked = 0; /* a flag */

  LEVEL l;

  /* task_join is a cancellation point... if the task is suspended

     the control on the status is done in task_kill */

  task_testcancel();

  /* some controls on the task p */

  if (p<0 || p>=MAX_PROC)                       return ESRCH;

  if (proc_table[p].status == FREE &&

      !(proc_table[p].control & WAIT_FOR_JOIN)) return ESRCH;

  if (!(proc_table[p].control & TASK_JOINABLE)) return EINVAL;

  proc_table[exec_shadow].context = kern_context_save();

  /* first, if it is the first time that the task_join is called,

     register the cancellation point */

  if (taskjoin_once) {

    taskjoin_once = 0;

    register_cancellation_point(taskjoin_cancellation_point, NULL);

  }

  if (proc_table[p].waiting_for_me != NIL) {

    kern_context_load(proc_table[exec_shadow].context);

    return EINVAL;

  }

  /* deadlock checks; we check the shadow chain to prevent cycles */

  x = p;

  do {

    x = proc_table[x].shadow;

    if (x == exec_shadow) {

      kern_context_load(proc_table[exec_shadow].context);

      return EDEADLK;

    }

  } while (x != proc_table[x].shadow);

  /* we prepare all the stuffs for joining the target task... */

  if (!(proc_table[p].control & WAIT_FOR_JOIN)) {

    /* the target task is already running... so we block yhe current task

       on it!!!

       Note: It is not correct to set only the shadow and reschedule, as done

       with the mutexes, because there is no inheritance with join...

       Normally we have to call task_extract because blocking on join is

       like blocking on a classic semaphore.

       Althought, we set the shadow because:

       - if the task call task_join when holding a mutex (AAARRRGGHHH!!!)

         the system continue working...

       - The deadlock detection strategy works on shadows...

       Setting shadows means also that implementation of mutexes that

       manage shadows in a strange way WILL NOT WORK with task_join

       (for example, the srp.c module doesn't work with task_join) */

    proc_table[p].waiting_for_me = exec_shadow;

    proc_table[exec_shadow].shadow = p;

    kern_epilogue_macro();

    /* now, we block the current task, waiting the end of the target task */

    l = proc_table[exec_shadow].task_level;

    level_table[l]->public_block(l,exec_shadow);

    proc_table[exec_shadow].status = WAIT_JOIN;

    exec = exec_shadow = -1;

    scheduler();

    /* note that we don't use kern_context_load because when rescheduled

       we remain in kernel mode... */

    ll_context_to(proc_table[exec_shadow].context);

    blocked = 1;

  }

  /* task-join is a cancellation point; if the task is killed while it is

     waiting on a join, the task-kill set the kill-request bit and wake up

     the task, so it can die :-) */

  task_testcancel();

  /* the target task is terminated... we reset the WAIT_FOR_JOIN flag

     so the descriptor can be reused by task_create; if the descriptor was

     already discarded by the task_create, we reinsert it into the free

     queue */

  proc_table[p].control &= ~WAIT_FOR_JOIN;

  if (proc_table[p].control & DESCRIPTOR_DISCARDED)

    iq_insertfirst(p, &freedesc);

  if (value)

    *value = proc_table[p].return_value;

  if (blocked) {

    /* the ll_context_to is already done... */

    kern_deliver_pending_signals();

    sti();

  }

  else

    /* we did a kern_context_save before... */

    kern_context_load(proc_table[exec_shadow].context);

  return 0;

}

/*+ this function set the detach state of a task to joinable. This function

    is not present in Posix standard...

    returns ESRCH if p is non correct +*/

int task_joinable(PID p)

{

  SYS_FLAGS f;

  if (p<0 || p>=MAX_PROC)                       return ESRCH;

  if (proc_table[p].status == FREE)             return ESRCH;

  f = kern_fsave();

  proc_table[p].control |= TASK_JOINABLE;

  kern_frestore(f);

  return 0;

}

/*+ this function set the detach state of a task to detached. This function

    works as the posix's pthread_detach

    returns EINVAL if p can't be joined (or currently a task has done a

    join on it (condition not provided in posix)

    ESRCH if p is not correct +*/

int task_unjoinable(PID p)

{

  SYS_FLAGS f;

  if (p<0 || p>=MAX_PROC)                       return ESRCH;

  if (proc_table[p].status == FREE)             return ESRCH;

  f = kern_fsave();

  if (!(proc_table[p].control & TASK_JOINABLE) ||

      proc_table[p].waiting_for_me != NIL) {

    kern_frestore(f);

    return EINVAL;

  }

  proc_table[p].control |= TASK_JOINABLE;

  kern_frestore(f);

  return 0;

}