nptl/pthread_cond_signal.c

   1 /* Copyright (C) 2003-2016 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>, 2003.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <endian.h>
  20 #include <errno.h>
  21 #include <sysdep.h>
  22 #include <lowlevellock.h>
  23 #include <pthread.h>
  24 #include <pthreadP.h>
  25
  26 #include <shlib-compat.h>
  27 #include <kernel-features.h>
  28 #include <stap-probe.h>
  29
  30
  31 int
  32 __pthread_cond_signal (pthread_cond_t *cond)
  33 {
  34   int pshared = (cond->__data.__mutex == (void *) ~0l)
  35                 ? LLL_SHARED : LLL_PRIVATE;
  36
  37   LIBC_PROBE (cond_signal, 1, cond);
  38
  39   /* Make sure we are alone.  */
  40   lll_lock (cond->__data.__lock, pshared);
  41
  42   /* Are there any waiters to be woken?  */
  43   if (cond->__data.__total_seq > cond->__data.__wakeup_seq)
  44     {
  45       /* Yes.  Mark one of them as woken.  */
  46       ++cond->__data.__wakeup_seq;
  47       ++cond->__data.__futex;
  48
  49 #if (defined lll_futex_cmp_requeue_pi \
  50      && defined __ASSUME_REQUEUE_PI)
  51       pthread_mutex_t *mut = cond->__data.__mutex;
  52
  53       if (USE_REQUEUE_PI (mut)
  54         /* This can only really fail with a ENOSYS, since nobody can modify
  55            futex while we have the cond_lock.  */
  56           && lll_futex_cmp_requeue_pi (&cond->__data.__futex, 1, 0,
  57                                        &mut->__data.__lock,
  58                                        cond->__data.__futex, pshared) == 0)
  59         {
  60           lll_unlock (cond->__data.__lock, pshared);
  61           return 0;
  62         }
  63       else
  64 #endif
  65         /* Wake one.  */
  66         if (! __builtin_expect (lll_futex_wake_unlock (&cond->__data.__futex,
  67                                                        1, 1,
  68                                                        &cond->__data.__lock,
  69                                                        pshared), 0))
  70           return 0;
  71
  72       /* Fallback if neither of them work.  */
  73       lll_futex_wake (&cond->__data.__futex, 1, pshared);
  74     }
  75
  76   /* We are done.  */
  77   lll_unlock (cond->__data.__lock, pshared);
  78
  79   return 0;
  80 }
  81
  82 versioned_symbol (libpthread, __pthread_cond_signal, pthread_cond_signal,
  83                   GLIBC_2_3_2);