nuttx/sched/pthread/pthread_mutexconsistent.c

/****************************************************************************
 * sched/pthread/pthread_mutexconsistent.c
 *
 *   Copyright (C) 2017 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <pthread.h>
#include <sched.h>
#include <assert.h>
#include <errno.h>

#include <nuttx/semaphore.h>

#include "pthread/pthread.h"

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: pthread_mutex_consistent
 *
 * Description:
 *   If mutex is a robust mutex in an inconsistent state, the
 *   pthread_mutex_consistent() function can be used to mark the state
 *   protected by the mutex referenced by mutex as consistent again.
 *
 *   If an owner of a robust mutex terminates while holding the mutex, the
 *   mutex becomes inconsistent and the next thread that acquires the mutex
 *   lock will be notified of the state by the return value EOWNERDEAD.
 *   In this case, the mutex does not become normally usable again until the
 *   state is marked consistent.
 *
 *   If the thread which acquired the mutex lock with the return value
 *   EOWNERDEAD terminates before calling either pthread_mutex_consistent()
 *   or pthread_mutex_unlock(), the next thread that acquires the mutex lock
 *   will be notified about the state of the mutex by the return value
 *   EOWNERDEAD.
 *
 *   The behavior is undefined if the value specified by the mutex argument
 *   to pthread_mutex_consistent() does not refer to an initialized mutex.
 *
 * Input Parameters:
 *   mutex -- a reference to the mutex to be made consistent
 *
 * Returned Value:
 *   Upon successful completion, the pthread_mutex_consistent() function
 *   will return zero. Otherwise, an error value will be returned to
 *   indicate the error.
 *
 ****************************************************************************/

int pthread_mutex_consistent(FAR pthread_mutex_t *mutex)
{
  int ret = EINVAL;
  int status;

  sinfo("mutex=0x%p\n", mutex);
  DEBUGASSERT(mutex != NULL);

  if (mutex != NULL)
    {
      /* Make sure the mutex is stable while we make the following checks. */

      sched_lock();

      /* Is the mutex available? */

      DEBUGASSERT(mutex->pid != 0); /* < 0: available, >0 owned, ==0 error */
      if (mutex->pid >= 0)
        {
          /* No.. Verify that the thread associated with the PID still
           * exists.  We may be destroying the mutex after cancelling a
           * pthread and the mutex may have been in a bad state owned by
           * the dead pthread.  NOTE: The following is unspecified behavior
           * (see pthread_mutex_consistent()).
           *
           * If the holding thread is still valid, then we should be able to
           * map its PID to the underlying TCB.  That is what sched_gettcb()
           * does.
           */

          if (sched_gettcb(mutex->pid) == NULL)
            {
              /* The thread associated with the PID no longer exists */

              mutex->pid    = -1;
              mutex->flags &= _PTHREAD_MFLAGS_ROBUST;
#ifdef CONFIG_PTHREAD_MUTEX_TYPES
              mutex->nlocks = 0;
#endif
              /* Reset the semaphore.  This has the same affect as if the
               * dead task had called pthread_mutex_unlock().
               */

              status = nxsem_reset((FAR sem_t *)&mutex->sem, 1);
              if (status < 0)
                {
                  ret = -status;
                }
              else
                {
                  ret = OK;
                }
            }

          /* Otherwise the mutex is held by some active thread.  Let's not
           * touch anything!
           */
        }
      else
        {
          /* There is no holder of the mutex.  Just make sure the
           * inconsistent flag is cleared and the number of locks is zero.
           */

          mutex->flags &= _PTHREAD_MFLAGS_ROBUST;
#ifdef CONFIG_PTHREAD_MUTEX_TYPES
          mutex->nlocks = 0;
#endif
          ret = OK;
        }

      sched_unlock();
    }

  sinfo("Returning %d\n", ret);
  return ret;
}