nptl/pthread_mutex_setprioceiling.c

   1 /* Set current priority ceiling of pthread_mutex_t.
   2    Copyright (C) 2006, 2007 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Jakub Jelinek <jakub@redhat.com>, 2006.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 #include <stdbool.h>
  22 #include <errno.h>
  23 #include <pthreadP.h>
  24
  25
  26 int
  27 pthread_mutex_setprioceiling (mutex, prioceiling, old_ceiling)
  28      pthread_mutex_t *mutex;
  29      int prioceiling;
  30      int *old_ceiling;
  31 {
  32   /* The low bits of __kind aren't ever changed after pthread_mutex_init,
  33      so we don't need a lock yet.  */
  34   if ((mutex->__data.__kind & PTHREAD_MUTEX_PRIO_PROTECT_NP) == 0)
  35     return EINVAL;
  36
  37   if (__sched_fifo_min_prio == -1)
  38     __init_sched_fifo_prio ();
  39
  40   if (__builtin_expect (prioceiling < __sched_fifo_min_prio, 0)
  41       || __builtin_expect (prioceiling > __sched_fifo_max_prio, 0)
  42       || __builtin_expect ((prioceiling
  43                             & (PTHREAD_MUTEXATTR_PRIO_CEILING_MASK
  44                                >> PTHREAD_MUTEXATTR_PRIO_CEILING_SHIFT))
  45                            != prioceiling, 0))
  46     return EINVAL;
  47
  48   /* Check whether we already hold the mutex.  */
  49   bool locked = false;
  50   if (mutex->__data.__owner == THREAD_GETMEM (THREAD_SELF, tid))
  51     {
  52       if (mutex->__data.__kind == PTHREAD_MUTEX_PP_ERRORCHECK_NP)
  53         return EDEADLK;
  54
  55       if (mutex->__data.__kind == PTHREAD_MUTEX_PP_RECURSIVE_NP)
  56         locked = true;
  57     }
  58
  59   int oldval = mutex->__data.__lock;
  60   if (! locked)
  61     do
  62       {
  63         /* Need to lock the mutex, but without obeying the priority
  64            protect protocol.  */
  65         int ceilval = (oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK);
  66
  67         oldval = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
  68                                                       ceilval | 1, ceilval);
  69         if (oldval == ceilval)
  70           break;
  71
  72         do
  73           {
  74             oldval
  75               = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
  76                                                      ceilval | 2,
  77                                                      ceilval | 1);
  78
  79             if ((oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK) != ceilval)
  80               break;
  81
  82             if (oldval != ceilval)
  83               lll_futex_wait (&mutex->__data.__lock, ceilval | 2,
  84                               // XYZ check mutex flag
  85                               LLL_SHARED);
  86           }
  87         while (atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
  88                                                     ceilval | 2, ceilval)
  89                != ceilval);
  90
  91         if ((oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK) != ceilval)
  92           continue;
  93       }
  94     while (0);
  95
  96   int oldprio = (oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK)
  97                 >> PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
  98   if (locked)
  99     {
 100       int ret = __pthread_tpp_change_priority (oldprio, prioceiling);
 101       if (ret)
 102         return ret;
 103     }
 104
 105   if (old_ceiling != NULL)
 106     *old_ceiling = oldprio;
 107
 108   int newlock = 0;
 109   if (locked)
 110     newlock = (mutex->__data.__lock & ~PTHREAD_MUTEX_PRIO_CEILING_MASK);
 111   mutex->__data.__lock = newlock
 112                          | (prioceiling << PTHREAD_MUTEX_PRIO_CEILING_SHIFT);
 113   atomic_full_barrier ();
 114
 115   lll_futex_wake (&mutex->__data.__lock, INT_MAX,
 116                   // XYZ check mutex flag
 117                   LLL_SHARED);
 118
 119   return 0;
 120 }