compat_futex.c

   1 /*
   2  * compat_futex.c
   3  *
   4  * Userspace RCU library - sys_futex compatibility code
   5  *
   6  * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   7  *
   8  * This library is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; either
  11  * version 2.1 of the License, or (at your option) any later version.
  12  *
  13  * This library is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with this library; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  21  */
  22
  23 #include <stdio.h>
  24 #include <pthread.h>
  25 #include <signal.h>
  26 #include <assert.h>
  27 #include <errno.h>
  28 #include <poll.h>
  29 #include <stdint.h>
  30
  31 #include <urcu/arch.h>
  32 #include <urcu/futex.h>
  33
  34 /*
  35  * Using attribute "weak" for __urcu_compat_futex_lock and
  36  * __urcu_compat_futex_cond. Those are globally visible by the entire
  37  * program, even though many shared objects may have their own version.
  38  * The first version that gets loaded will be used by the entire program
  39  * (executable and all shared objects).
  40  */
  41
  42 __attribute__((weak))
  43 pthread_mutex_t __urcu_compat_futex_lock = PTHREAD_MUTEX_INITIALIZER;
  44 __attribute__((weak))
  45 pthread_cond_t __urcu_compat_futex_cond = PTHREAD_COND_INITIALIZER;
  46
  47 /*
  48  * _NOT SIGNAL-SAFE_. pthread_cond is not signal-safe anyway. Though.
  49  * For now, timeout, uaddr2 and val3 are unused.
  50  * Waiter will relinquish the CPU until woken up.
  51  */
  52
  53 int compat_futex_noasync(int32_t *uaddr, int op, int32_t val,
  54         const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
  55 {
  56         int ret, gret = 0;
  57
  58         /*
  59          * Check if NULL. Don't let users expect that they are taken into
  60          * account.
  61          */
  62         assert(!timeout);
  63         assert(!uaddr2);
  64         assert(!val3);
  65
  66         /*
  67          * memory barriers to serialize with the previous uaddr modification.
  68          */
  69         cmm_smp_mb();
  70
  71         ret = pthread_mutex_lock(&__urcu_compat_futex_lock);
  72         assert(!ret);
  73         switch (op) {
  74         case FUTEX_WAIT:
  75                 if (*uaddr != val)
  76                         goto end;
  77                 pthread_cond_wait(&__urcu_compat_futex_cond, &__urcu_compat_futex_lock);
  78                 break;
  79         case FUTEX_WAKE:
  80                 pthread_cond_broadcast(&__urcu_compat_futex_cond);
  81                 break;
  82         default:
  83                 gret = -EINVAL;
  84         }
  85 end:
  86         ret = pthread_mutex_unlock(&__urcu_compat_futex_lock);
  87         assert(!ret);
  88         return gret;
  89 }
  90
  91 /*
  92  * _ASYNC SIGNAL-SAFE_.
  93  * For now, timeout, uaddr2 and val3 are unused.
  94  * Waiter will busy-loop trying to read the condition.
  95  */
  96
  97 int compat_futex_async(int32_t *uaddr, int op, int32_t val,
  98         const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
  99 {
 100         /*
 101          * Check if NULL. Don't let users expect that they are taken into
 102          * account.
 103          */
 104         assert(!timeout);
 105         assert(!uaddr2);
 106         assert(!val3);
 107
 108         /*
 109          * Ensure previous memory operations on uaddr have completed.
 110          */
 111         cmm_smp_mb();
 112
 113         switch (op) {
 114         case FUTEX_WAIT:
 115                 while (*uaddr == val)
 116                         poll(NULL, 0, 10);
 117                 break;
 118         case FUTEX_WAKE:
 119                 break;
 120         default:
 121                 return -EINVAL;
 122         }
 123         return 0;
 124 }