glibc/nptl/pthread_cond_signal.c

/* Copyright (C) 2003-2016 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Martin Schwidefsky <schwidefsky@de.ibm.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 <endian.h>
#include <errno.h>
#include <sysdep.h>
#include <lowlevellock.h>
#include <pthread.h>
#include <pthreadP.h>

#include <shlib-compat.h>
#include <kernel-features.h>
#include <stap-probe.h>


int
__pthread_cond_signal (pthread_cond_t *cond)
{
  int pshared = (cond->__data.__mutex == (void *) ~0l)
		? LLL_SHARED : LLL_PRIVATE;

  LIBC_PROBE (cond_signal, 1, cond);

  /* Make sure we are alone.  */
  lll_lock (cond->__data.__lock, pshared);

  /* Are there any waiters to be woken?  */
  if (cond->__data.__total_seq > cond->__data.__wakeup_seq)
    {
      /* Yes.  Mark one of them as woken.  */
      ++cond->__data.__wakeup_seq;
      ++cond->__data.__futex;

#if (defined lll_futex_cmp_requeue_pi \
     && defined __ASSUME_REQUEUE_PI)
      pthread_mutex_t *mut = cond->__data.__mutex;

      if (USE_REQUEUE_PI (mut)
	/* This can only really fail with a ENOSYS, since nobody can modify
	   futex while we have the cond_lock.  */
	  && lll_futex_cmp_requeue_pi (&cond->__data.__futex, 1, 0,
				       &mut->__data.__lock,
				       cond->__data.__futex, pshared) == 0)
	{
	  lll_unlock (cond->__data.__lock, pshared);
	  return 0;
	}
      else
#endif
	/* Wake one.  */
	if (! __builtin_expect (lll_futex_wake_unlock (&cond->__data.__futex,
						       1, 1,
						       &cond->__data.__lock,
						       pshared), 0))
	  return 0;

      /* Fallback if neither of them work.  */
      lll_futex_wake (&cond->__data.__futex, 1, pshared);
    }

  /* We are done.  */
  lll_unlock (cond->__data.__lock, pshared);

  return 0;
}

versioned_symbol (libpthread, __pthread_cond_signal, pthread_cond_signal,
		  GLIBC_2_3_2);