/* sem_post -- post to a POSIX semaphore.  Generic futex-using version.

   Copyright (C) 2003-2018 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.

   The GNU C 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 2.1 of the License, or (at your option) any later version.

   The GNU C 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 the GNU C Library; if not, see

   <http://www.gnu.org/licenses/>.  */

#include <atomic.h>

#include <errno.h>

#include <sysdep.h>

#include <lowlevellock.h>	/* lll_futex* used by the old code.  */

#include <futex-internal.h>

#include <internaltypes.h>

#include <semaphore.h>

#include <shlib-compat.h>

/* See sem_wait for an explanation of the algorithm.  */

int

__new_sem_post (sem_t *sem)

{

  struct new_sem *isem = (struct new_sem *) sem;

  int private = isem->private;

#if __HAVE_64B_ATOMICS

  /* Add a token to the semaphore.  We use release MO to make sure that a

     thread acquiring this token synchronizes with us and other threads that

     added tokens before (the release sequence includes atomic RMW operations

     by other threads).  */

  /* TODO Use atomic_fetch_add to make it scale better than a CAS loop?  */

  uint64_t d = atomic_load_relaxed (&isem->data);

  do

    {

      if ((d & SEM_VALUE_MASK) == SEM_VALUE_MAX)

	{

	  __set_errno (EOVERFLOW);

	  return -1;

	}

    }

  while (!atomic_compare_exchange_weak_release (&isem->data, &d, d + 1));

  /* If there is any potentially blocked waiter, wake one of them.  */

  if ((d >> SEM_NWAITERS_SHIFT) > 0)

    futex_wake (((unsigned int *) &isem->data) + SEM_VALUE_OFFSET, 1, private);

#else

  /* Add a token to the semaphore.  Similar to 64b version.  */

  unsigned int v = atomic_load_relaxed (&isem->value);

  do

    {

      if ((v >> SEM_VALUE_SHIFT) == SEM_VALUE_MAX)

	{

	  __set_errno (EOVERFLOW);

	  return -1;

	}

    }

  while (!atomic_compare_exchange_weak_release

	 (&isem->value, &v, v + (1 << SEM_VALUE_SHIFT)));

  /* If there is any potentially blocked waiter, wake one of them.  */

  if ((v & SEM_NWAITERS_MASK) != 0)

    futex_wake (&isem->value, 1, private);

#endif

  return 0;

}

versioned_symbol (libpthread, __new_sem_post, sem_post, GLIBC_2_1);

#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)

int

attribute_compat_text_section

__old_sem_post (sem_t *sem)

{

  int *futex = (int *) sem;

  /* We must need to synchronize with consumers of this token, so the atomic

     increment must have release MO semantics.  */

  atomic_write_barrier ();

  (void) atomic_increment_val (futex);

  /* We always have to assume it is a shared semaphore.  */

  int err = lll_futex_wake (futex, 1, LLL_SHARED);

  if (__builtin_expect (err, 0) < 0)

    {

      __set_errno (-err);

      return -1;

    }

  return 0;

}

compat_symbol (libpthread, __old_sem_post, sem_post, GLIBC_2_0);

#endif