nptl/pthread_cond_signal.c

   1 /* Copyright (C) 2003-2015 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 (cond)
  33      pthread_cond_t *cond;
  34 {
  35   int pshared = (cond->__data.__mutex == (void *) ~0l)
  36                 ? LLL_SHARED : LLL_PRIVATE;
  37
  38   LIBC_PROBE (cond_signal, 1, cond);
  39
  40   /* Make sure we are alone.  */
  41   lll_lock (cond->__data.__lock, pshared);
  42
  43   /* Are there any waiters to be woken?  */
  44   if (cond->__data.__total_seq > cond->__data.__wakeup_seq)
  45     {
  46       /* Yes.  Mark one of them as woken.  */
  47       ++cond->__data.__wakeup_seq;
  48       ++cond->__data.__futex;
  49
  50 #if (defined lll_futex_cmp_requeue_pi \
  51      && defined __ASSUME_REQUEUE_PI)
  52       pthread_mutex_t *mut = cond->__data.__mutex;
  53
  54       if (USE_REQUEUE_PI (mut)
  55         /* This can only really fail with a ENOSYS, since nobody can modify
  56            futex while we have the cond_lock.  */
  57           && lll_futex_cmp_requeue_pi (&cond->__data.__futex, 1, 0,
  58                                        &mut->__data.__lock,
  59                                        cond->__data.__futex, pshared) == 0)
  60         {
  61           lll_unlock (cond->__data.__lock, pshared);
  62           return 0;
  63         }
  64       else
  65 #endif
  66         /* Wake one.  */
  67         if (! __builtin_expect (lll_futex_wake_unlock (&cond->__data.__futex,
  68                                                        1, 1,
  69                                                        &cond->__data.__lock,
  70                                                        pshared), 0))
  71           return 0;
  72
  73       /* Fallback if neither of them work.  */
  74       lll_futex_wake (&cond->__data.__futex, 1, pshared);
  75     }
  76
  77   /* We are done.  */
  78   lll_unlock (cond->__data.__lock, pshared);
  79
  80   return 0;
  81 }
  82
  83 versioned_symbol (libpthread, __pthread_cond_signal, pthread_cond_signal,
  84                   GLIBC_2_3_2);