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 static pthread_mutex_t compat_futex_lock = PTHREAD_MUTEX_INITIALIZER;
  35 static pthread_cond_t compat_futex_cond = PTHREAD_COND_INITIALIZER;
  36
  37 /*
  38  * _NOT SIGNAL-SAFE_. pthread_cond is not signal-safe anyway. Though.
  39  * For now, timeout, uaddr2 and val3 are unused.
  40  * Waiter will relinquish the CPU until woken up.
  41  */
  42
  43 int compat_futex_noasync(int32_t *uaddr, int op, int32_t val,
  44         const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
  45 {
  46         int ret, i, gret = 0;
  47
  48         /*
  49          * Check if NULL. Don't let users expect that they are taken into
  50          * account.
  51          */
  52         assert(!timeout);
  53         assert(!uaddr2);
  54         assert(!val3);
  55
  56         /*
  57          * memory barriers to serialize with the previous uaddr modification.
  58          */
  59         cmm_smp_mb();
  60
  61         ret = pthread_mutex_lock(&compat_futex_lock);
  62         assert(!ret);
  63         switch (op) {
  64         case FUTEX_WAIT:
  65                 if (*uaddr != val)
  66                         goto end;
  67                 pthread_cond_wait(&compat_futex_cond, &compat_futex_lock);
  68                 break;
  69         case FUTEX_WAKE:
  70                 for (i = 0; i < val; i++)
  71                         pthread_cond_signal(&compat_futex_cond);
  72                 break;
  73         default:
  74                 gret = -EINVAL;
  75         }
  76 end:
  77         ret = pthread_mutex_unlock(&compat_futex_lock);
  78         assert(!ret);
  79         return gret;
  80 }
  81
  82 /*
  83  * _ASYNC SIGNAL-SAFE_.
  84  * For now, timeout, uaddr2 and val3 are unused.
  85  * Waiter will busy-loop trying to read the condition.
  86  */
  87
  88 int compat_futex_async(int32_t *uaddr, int op, int32_t val,
  89         const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
  90 {
  91         /*
  92          * Check if NULL. Don't let users expect that they are taken into
  93          * account.
  94          */
  95         assert(!timeout);
  96         assert(!uaddr2);
  97         assert(!val3);
  98
  99         /*
 100          * Ensure previous memory operations on uaddr have completed.
 101          */
 102         cmm_smp_mb();
 103
 104         switch (op) {
 105         case FUTEX_WAIT:
 106                 while (*uaddr == val)
 107                         poll(NULL, 0, 10);
 108                 break;
 109         case FUTEX_WAKE:
 110                 break;
 111         default:
 112                 return -EINVAL;
 113         }
 114         return 0;
 115 }