pthread_timechange_handler_np.c

/*
 * pthread_timechange_handler_np.c
 *
 * Description:
 * This translation unit implements miscellaneous thread functions.
 *
 * --------------------------------------------------------------------------
 *
 *      Pthreads4w - POSIX Threads for Windows
 *      Copyright 1998 John E. Bossom
 *      Copyright 1999-2018, Pthreads4w contributors
 *
 *      Homepage: https://sourceforge.net/projects/pthreads4w/
 *
 *      The current list of contributors is contained
 *      in the file CONTRIBUTORS included with the source
 *      code distribution. The list can also be seen at the
 *      following World Wide Web location:
 *
 *      https://sourceforge.net/p/pthreads4w/wiki/Contributors/
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#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-win32 converts absolute times to intervals in
 *    order to make use of the underlying Win32, 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;
  __ptw32_mcs_local_node_t node;

  __ptw32_mcs_lock_acquire(&__ptw32_cond_list_lock, &node);

  cv = __ptw32_cond_list_head;

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

  __ptw32_mcs_lock_release(&node);

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