relibc_pthreads-emb/pthread_timechange_handler_np.c

/*
 * pthread_timechange_handler_np.c
 *
 * Description:
 * This translation unit implements miscellaneous thread functions.
 *
 * --------------------------------------------------------------------------
 *
 *      Pthreads-embedded (PTE) - POSIX Threads Library for embedded systems
 *      Copyright(C) 2008 Jason Schmidlapp
 *
 *      Contact Email: jschmidlapp@users.sourceforge.net
 *
 *
 *      Based upon Pthreads-win32 - POSIX Threads Library for Win32
 *      Copyright(C) 1998 John E. Bossom
 *      Copyright(C) 1999,2005 Pthreads-win32 contributors
 *
 *      Contact Email: rpj@callisto.canberra.edu.au
 *
 *      The original list of contributors to the Pthreads-win32 project
 *      is contained in the file CONTRIBUTORS.ptw32 included with the
 *      source code distribution. The list can also be seen at the
 *      following World Wide Web location:
 *      http://sources.redhat.com/pthreads-win32/contributors.html
 *
 *      This library is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU Lesser General Public
 *      License as published by the Free Software Foundation; either
 *      version 2 of the License, or (at your option) any later version.
 *
 *      This library 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
 *      Lesser General Public License for more details.
 *
 *      You should have received a copy of the GNU Lesser General Public
 *      License along with this library in the file COPYING.LIB;
 *      if not, write to the Free Software Foundation, Inc.,
 *      59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 */

#include "pthread.h"
#include "implement.h"

/*
 * Notes on handling system time adjustments (especially negative ones).
 * ---------------------------------------------------------------------
 *
 * This solution was suggested by Alexander Terekhov, but any errors
 * in the implementation are mine - [Ross Johnson]
 *
 * 1) The problem: threads doing a timedwait on a CV may expect to timeout
 *    at a specific absolute time according to a system timer. If the
 *    system clock is adjusted backwards then those threads sleep longer than
 *    expected. Also, pthreads-embedded converts absolute times to intervals in
 *    order to make use of the underlying OS, and so waiting threads may
 *    awake before their proper abstimes.
 *
 * 2) We aren't able to distinquish between threads on timed or untimed waits,
 *    so we wake them all at the time of the adjustment so that they can
 *    re-evaluate their conditions and re-compute their timeouts.
 *
 * 3) We rely on correctly written applications for this to work. Specifically,
 *    they must be able to deal properly with spurious wakeups. That is,
 *    they must re-test their condition upon wakeup and wait again if
 *    the condition is not satisfied.
 */

void *
pthread_timechange_handler_np (void *arg)
/*
 * ------------------------------------------------------
 * DOCPUBLIC
 *      Broadcasts all CVs to force re-evaluation and
 *      new timeouts if required.
 *
 * PARAMETERS
 *      NONE
 *
 *
 * DESCRIPTION
 *      Broadcasts all CVs to force re-evaluation and
 *      new timeouts if required.
 *
 *      This routine may be passed directly to pthread_create()
 *      as a new thread in order to run asynchronously.
 *
 *
 * RESULTS
 *              0               successfully broadcast all CVs
 *              EAGAIN          Not all CVs were broadcast
 *
 * ------------------------------------------------------
 */
{
  int result = 0;
  pthread_cond_t cv;


  pte_osMutexLock (pte_cond_list_lock);

  cv = pte_cond_list_head;

  while (cv != NULL && 0 == result)
    {
      result = pthread_cond_broadcast (&cv);
      cv = cv->next;
    }

  pte_osMutexUnlock(pte_cond_list_lock);

  return (void *) (result != 0 ? EAGAIN : 0);
}