lib/libc/sysvipc/lock_generic.c

   1 /*-
   2  * Copyright (c) 2005 David Xu <davidxu@freebsd.org>
   3  * Copyright (c) 2005 Matthew Dillon <dillon@backplane.com>
   4  *
   5  * All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  19  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  20  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  26  * SUCH DAMAGE.
  27  */
  28
  29 #include <assert.h>
  30 #include <errno.h>
  31 #include <unistd.h>
  32 #include <sys/time.h>
  33
  34 #include "sysvipc_lock_generic.h"
  35
  36 /*
  37  * This function is used to acquire a contested lock.
  38  */
  39 int
  40 __sysv_umtx_lock(volatile umtx_t *mtx, int timo)
  41 {
  42         int v, errval, ret = 0;
  43
  44         /* contested */
  45         do {
  46                 v = *mtx;
  47                 if (v == 2 || atomic_cmpset_acq_int(mtx, 1, 2)) {
  48                         if (timo == 0)
  49                                 umtx_sleep(mtx, 2, timo);
  50                         else if ( (errval = umtx_sleep(mtx, 2, timo)) > 0) {
  51                                 if (errval == EAGAIN) {
  52                                         if (atomic_cmpset_acq_int(mtx, 0, 2))
  53                                                 ret = 0;
  54                                         else
  55                                                 ret = ETIMEDOUT;
  56                                         break;
  57                                 }
  58                         }
  59                 }
  60         } while (!atomic_cmpset_acq_int(mtx, 0, 2));
  61
  62         return (ret);
  63 }
  64
  65 void
  66 __sysv_umtx_unlock(volatile umtx_t *mtx)
  67 {
  68         int v;
  69
  70         for (;;) {
  71                 v = *mtx;
  72                 if (atomic_cmpset_acq_int(mtx, v, v-1)) {
  73                         if (v != 1) {
  74                                 *mtx = 0;
  75                                 umtx_wakeup(mtx, 1);
  76                         }
  77                         break;
  78                 }
  79         }
  80 }